Are the fossil sites in Hadar geographically separated?

Are the fossil sites in Hadar geographically separated?

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The Hadar fossil record is made up of, from oldest to youngest, the Basal Member, Sidi Hakoma Member, Denen Dora Member, and Kada Hadar Member.

Are these regions geographically distinct, or, are they layers on top of another on the same geographical region?

Here is a map of the region where they found the Lucy skeleton.

The researchers speak of the Hadar formation at Dikika, so they are giving it an expanse of 10-15 kilometers at least.

it's quite flat as well.

Why do you want to know?


Field research at the fossil-bearing deposits in the Afar Depression began in the 1970s. Prior to this, hominin fossils older than 3.0 Mya consisted of only a handful of fragments. During Phase I, the International Afar Research Expedition to Hadar, Ethiopia collected some 240 fossil hominins from Hadar over a time range of 3.0–3.4 Mya. Along with hominin fossils from Laetoli, they were deemed a new species, Australopithecus afarensis. This taxon was posited as the last common ancestor to robust Australopithecus and the Homo lineage in eastern Africa. Phase II research under the Hadar Research Project has added strength to the Phase I results, including the first association of a Homo fossil with stone tools at 2.4 Mya. This presentation is a cursory synopsis of the importance and implications of the hominin fossils recovered at Hadar during over the last 34 years.

Viewpoint: Yes, the fossils found by Louis and Mary Leakey and by Donald Johanson represent several hominid species.

Theories of human evolution are increasingly framed in terms of insights gained by the genetic analysis of human and nonhuman primate lineages. Using differences in DNA to estimate how long humans and chimps have been separate lines, scientists suggest that humans separated from the apes about 5 to 8 million years ago. Nevertheless, debates about the traditional source of information, i.e., the fossil evidence, are still complicated by the paucity of the evidence and disagreements about palaeontological systems of classification. Although thousands of hominid fossils have been collected, many specimens consist of only bits of bone or a few teeth. Indeed, it is sometimes said that all known hominid fossils could fit into one coffin. The discovery of any hominid fossil specimen, no matter how fragmentary, inevitably serves as the basis for endless speculation. Nevertheless, according to the eminent eighteenth-century French anatomist Baron Georges Cuvier (1769-1832), through knowledge of the comparative anatomy of living animals, many insights into the form and function of extinct creatures can be reconstructed by the analysis of a few bones.

Long Baseline Experiments

Most scientists agree that the fossil record provides evidence of 10 to 15 different species of early humans, but the relationships among these ancient species and their relationship, if any, to modern humans remains uncertain and controversial. The classification of various species of early humans, and the factors that influenced evolution and extinction are also subjects of debate. The conventional criteria for allocating fossil species to a particular genus have often been challenged for being ambiguous, inappropriate, and inconsistently applied. Arguments about the identity of fossil remains are complicated by evidence that suggests hominid species may have been quite variable, with some of the apparent variability due to sexual dimorphism, a characteristic often found among living nonhuman primates. Given the interesting variations found in hominid fossils, many paleoanthropologists agree that human remains exhibiting a unique set of traits should have a new species name.

The story of the search for the human ancestors and the debates about the relationships among the various species included in the catalog of early hominids is, in large part, the story of the Kenyan anthropologist Louis Leakey and his wife, paleoanthropologist Mary Leakey. The Leakeys stimulated and inspired many paleoanthropologists, including American Donald Johanson, to search for human ancestors and explore the relationship between humans and other primates. Few people have had more impact on the modern era of paleoanthropology than Leakey, the patriarch of a remarkable multi-generational family of anthropologists. The Leakeys were largely responsible for convincing scientists that the search for human ancestors must begin in Africa. When Louis Leakey began hunting for fossil hominids in the early 1930s, most anthropologists believed that early humans had originated somewhere in Asia because of previous discoveries of human fossils in Java (now Indonesia) and China. Leakey's son Richard Leakey, his wife Meave, and their daughter Louise, are carrying on with the work begun by Louis and Mary Leakey.

The Leakeys were not, of course, the first scientists to discover ancient human ancestors in Africa. The South African paleontologist Raymond Dart was one of the first to recognize the existence of the fossilized remains of primitive, but bipedal human ancestors. In 1925, Dart discovered the skull of an extinct primate at Taung, South Africa. According to Dart, the creature was not an ape, but it walked upright. Because its brain was only about 28 cu in (450 cc), too small for admission to the genus Homo, Dart established a new genus, Australopithecus (Southern apeman). He named the primitive creature Australopithecus africanus. Dart's contemporaries generally rejected his claims until Robert Broom, another South African paleontologist, discovered many more A. africanus skulls and other bones. Although brain size was originally considered the key to human evolution, many paleontologist now consider the evolution of bipedalism, the ability to walk on two legs, to be one of the most critical early differences between the human and the ape lineages. Habitual bipedalism, as opposed to the ability to stand upright like chimps, requires many anatomical adaptations, in both the upper and lower body. Such changes involve the pelvic bone, hip joints, leg bones, toes, S-shaped cure of the spine, and the position of the foramen magnum. Australopithicines did, however, have curved, elongated fingers and elongated arms, which suggests that, in addition to walking upright, they climbed trees like apes.

The discovery that brought worldwide attention to the Leakeys occurred in 1959 at Olduvai gorge in Tanzania, when Mary Leakey found the skull of a creature originally called Zinjanthropus boisei (East African man). Informally the fossil became known as Nutcracker Man, because of its robust skull and huge teeth. The specimen was an almost complete cranium, with a brain size of about 32 cu in (530 cc). The specimen was estimated to be dated about 1.8 million years ago. Today, this species is known as Australopithecus boisei.

During the 1960s the Leakeys and their son Jonathan discovered fossils remains that seemed to represent the oldest known primate with human characteristics. Leakey challenged contemporary ideas about the course of human evolution and established a new species name for these fossils—Homo habilis (Handy man). Louis Leakey thought that H. habilis was a tool-making contemporary of the australopithecines, with a brain size of about 43 cu in (700 cc). His designation of these remains as a new species belonging to the genus Homo was very controversial. Some critics argued that Leakey's H. habilis was based on insufficient material and that the remains in questions were actually a mixture of A. africanus and H. erectus. Others questioned the age of the fossil and concluded that Leakey's fossil should have been classified as a rather large-brained Australopithecus, rather than a small-brained Homo. Although H. habilis was originally very controversial, Leakey's designation of this new species was subsequently widely accepted, because the brain size was above the range for the australopithicines. Moreover, there were significant characteristics of the feet, the ratio of the length of the arms to the legs, and the shape and size of the molar teeth, premolar teeth, and jaws of H. habilis that distinguish it from those of contemporary australopithicines. Differences in the body size of various H. habilis specimens suggest a striking degree of sexual dimorphism.

In 1975 Mary Leakey discovered the jaws and teeth of at least 11 individuals at Laetoli, 30 mi (48 km) south of Olduvai Gorge. The fragments were found in sediments located between deposits of fossil volcanic ash dated at 3.35 and 3.75 million years. At the time these were the oldest known hominid fossils. Mary classified these remains as H. habilis. Mary made another remarkable discovery in 1978, a trail of fossilized hominid footprints that had been preserved in volcanic ash at the Laetoli site. The footprints seemed to be those of two adults and a child, probably made about 3.5 million years ago. The footprints definitely prove that australopithicines regularly walked bipedally, but the discovery led to a major controversy about the identity of the hominid species that made them. According to some anthropologists, the species Mary Leakey was studying at Laetoli was not H. habilis, but a new hominid species, A. afarensis, that Donald C. Johanson had recently discovered at Hadar, Ethiopia.

Donald Johanson is one of the best-known American paleoanthropologists and the founder of the Institute of Human Origins, a nonprofit research institution devoted to the study of pre-history. While working at Hadar in the Afar region of Ethiopia from 1972 to 1977, Johanson discovered hominid remains that were dated as 2.9 to 3.3 million years old. One of his finds was a small but humanlike knee, the first example of a hominid knee. He made his most famous discovery in 1974, the partial skeleton of a female australopithecine, popularly known as Lucy. The skeleton has been dated between 4 and 3 million years ago and was almost 40% complete, making Lucy the oldest, most complete human ancestor ever assembled. In 1975 Johanson's team found a collection of fossils at a single site that seemed to be the remains of some 13 individuals. The collection was nicknamed the First Family. Eventually still more hominid fossils were discovered, along with stone tools.

After analyzing the fossils with Timothy White, Johanson came to the conclusion that all the Afar fossils belonged to a new species. In 1978 Johanson and White named the new species Australopithecus afarensis. These discoveries and Johanson's interpretation created a major controversy among paleoanthropologists. Critics claimed that slight differences did not justify a new species name and said Johanson's A. afarensis should be considered a geographical subspecies of A. africanus. Johanson and his supporters argue that the anatomical differences between A. afarensis and other hominids are qualitatively and quantitatively beyond the normal variation found within a species. In addition to being older, Johanson pointed out that that the brain case of A. afarensis was smaller than that of H. habilis and A. africanus. There were also significant differences in the teeth, jaws, fingers, foot, and leg bones. Johanson argues that the differences between specimens justified assigning the Afar fossils to a new species.

Much of the controversy about creating a new species designation arose when Johanson argued that his Afar specimens belonged to the same species as Mary Leakey's Laetoli fossils. Based on apelike characteristics of the teeth and skull shared by no other fossil hominid, Johanson and White assigned both the Laetoli and Afar remains to A. afarensis. They claimed that this new species was more ancient and more primitive than any other hominid fossil. Mary and Richard Leakey criticized Johanson for proclaiming a new species too quickly, and suggested that the fossils could be a mixture of several different species. Other anthropologists, however, agreed that the features pointed out by Johanson were significant enough to distinguish the Afar and Laetoli fossils as different species.

In 1994 Meave Leakey found teeth and bone fragments similar to a fossil arm bone that had been discovered in 1965. In 1995 Meave classifed all these remains as belonging to a new species, Australopithecus anamensis. This very primitive australopithicene had an apelike skull, but leg bones apparently adapted to bipedalism. Ironically, A. anamensis appears to be quite similar to A. afarensis, the species that was the subject of a dispute between Mary Leakey and Johanson.

Despite the ambiguities involved in identifying and naming ancient ancestors, there is general agreement that the earliest human ancestors were the australopithecines. The most significant features distinguishing australopithecines from the apes were their small canine teeth and bipedalism. Members of this group appear to be the first mammals anatomically adapted for habitually walking on two legs. However, they had a brain size of about 24-34 cu in (400-550 cc), a low cranium, and a projecting face. The most primitive australopithecines are now placed in the genus Ardipithecus. In addition to the genus Australopithecus, some anthropologists have adopted the category Paranthropus.

At the beginning of the twenty-first century, several new fossil hominids discoveries were announced, and, as usual, greeted by debate about their identity and their relationship to other ancient ancestors. The announcement of the discovery of new hominid remains in 2001 sparked renewed controversy about the earliest hominid ancestors, as well as those of the chimpanzee. In 1990, French paleoanthropologists Brigitte Senut and Martin Pickford discovered a set of fossil fragments in Kenya 6 million years old, which they dubbed Millennium Man. Senut and Pickford classified the fossils as belonging to a new species, which they called Orrorin tugenensis (Original man, Tugen Hills region). One aspect of the controversy has been attributed to prior conflicts between Richard Leakey and Pickford. Nevertheless, the bones and teeth do show an interesting combination of features, which separate Orrorin from the australopithecines.

Within months of the report on O. tugenensis, Yohannes Haile-Selassie, of the University of California, Berkeley, announced a new find that cast doubt on the hominid status of Orronin and supported hominid status for A. ramidus, a species discovered in 1994 by an international team led by paleoanthropologist Timothy White. The fossils, found in the Middle Awash area of Ethiopia, are estimated to be between 5.2 and 5.8 million years old. Haile-Selassie argues that they represent an early form of A. ramidus, and appear to be from a hominid species closely related to the common ancestor of chimpanzees and humans. The debate about the status of O. tugenensis and A. ramidus could, therefore, provide insight into the lineage of chimpanzees and hominids.

Debates about hominid fossils have been the one constant in the rapidly changing field of paleoanthropology. The conflict between the Leakeys and Johanson is well known, but disputes continue into the twenty-first century with the discovery of each new fossil.

Are the fossil sites in Hadar geographically separated? - Biology

For many decades, a disparity between the resolution of long and continuous marine paleoclimate records versus fragmentary and time-averaged terrestrial records has hampered our ability to establish precise links between human evolution and major environmental changes. However, a recent proliferation of fieldwork, new drilling campaigns targeting highly detailed and relatively continuous paleolake records, and novel geochemical approaches are helping to assess terrestrial environmental dynamics at finer resolutions. Despite this progress, it remains the case that fauna, particularly hominins, are poorly sampled from the crucial time range between 3 and 2.5 million years ago because fossiliferous sediments dating to this interval are rare. Although prolific deposits of the Omo-Turkana Basin in Ethiopia and Kenya do contain sediments from this interval, the Hominin fossils are fragmentary and their taxonomic identities are uncertain. Sedimentary basins of the Afar in Ethiopia are highly fossiliferous, containing the most complete Hominin record of the past 6 million years, alongside diverse faunas and well-established chronologies, but the 3𔃀.5 million years ago interval is very poorly represented.

The Mille-Logya Project is a new palaeoanthropological site, dated from roughly 2.9 to 2.4 million years ago, at the northeast end of the well-known Plio-Pleistocene sites in the Awash Valley of the Afar Regional State, Ethiopia. Research at Mille-Logya started in 2012 and systematic geological and palaeontological surveys were conducted in 2014, 2015, 2016, 2018, and 2019.

The fossiliferous sediments exposed at Mille-Logya are generally younger than most of other known research areas in the region. Thus, they offer a unique opportunity to elucidate major events in Human evolution including the transition from Australopithecus to Homo, the emergence of Paranthropus, and the advent of manufactured stone tools. Furthermore, although Australopithecus afarensis is the most abundantly preserved Hominin from the region between 3.8 and 2.9 million years ago, its fate is largely unknown because of a regional hiatus in the sedimentary record of the Hadar Basin between 2.9 and 2.7 million years ago. Above this unconformity, the sediments of the Busidima Formation fill a local half graben near the western escarpment of the Ethiopian Rift. Compared to the largely lacustrine and peri-lacustrine Hadar Formation, the Busidima Formation exhibits a very different style of deposition, characterised by low sedimentation rates in almost exclusively episodic, high-energy fluvial settings, resulting in relatively poor fossil preservation. Meanwhile, during this same interval (2.9𔃀.7 million years ago), lacustrine and peri-lacustrine sediments were deposited at Mille-Logya and continue into younger horizons.

Alemseged et al.'s geological work offers new evidence for the northeast migration of the Hadar Basin, expanding our knowledge of the history of the basin substantially. Three new fossiliferous horizons with differing faunal composition have been identified suggesting in situ faunal change. While the fauna in the older unit is comparable to that at Hadar and Dikika, the younger units contain species that indicate more open conditions along with remains of Homo. New data from Mille-Logya reveal how Hominins and other fauna responded to environmental changes during this key period. Alemseged et al.'s results show a connection between geotectonics, sedimentary basin migration and an in situ faunal change. Alemseged et al. also provide new evidence that could potentially explain what happened to Australopithecus afarensis after 2.9 million years ago and what caused the dispersal to or the emergence of Homo in the region.

Stratigraphic surveys of the Mille-Logya area were geared toward broadening our understanding of the geological history of the region. To achieve this, it is crucial not only to establish chronological relationships between fossiliferous sites, but to investigate stratigraphic, structural and facies relationships between discontinuous exposures of sedimentary basins. Early geological maps of the region showed isolated Plio-Pleistocene sediments within the new site, amidst basalt flows attributed to the Afar Stratoid Series. In these broad-scale maps, the sediments were attributed to undifferentiated Quaternary strata or the White Series (Enkafala Beds both mapping units, were also used to indicate outcrops of the Hadar Formation, the latter having been much more thoroughly scrutinised since initial fossil discoveries at the Hadar site). Sediments in areas nearby broadly bracket and partly overlap with the strata of the Hadar Formation. Alemseged et al.'s work has identified three new fossiliferous stratigraphic units expanding our knowledge of the geological history of the region and providing context for our faunal and basin analysis.

Sedimentary exposures in the Mille-Logya area provide access to generally disconnected sections of up to about 60m in total thickness. Between these discontinuous exposures, extensive colluvial cover of volcanic, boulder- to cobble-sized material obscures most outcrop. Furthermore, a number of postdepositional faults divide the exposures into disconnected fault-bounded blocks. Hence, Alemseged et al.'s stratigraphic interpretations of relationships between sections are presently based on widespread marker beds, chemical groupings of interfingered basalts and tephras, nine new Argon⁴⁰/Argon³⁹ dates, and several magnetostratigraphic sections. These observations are sufficient to describe the overall stratigraphy, and to divide the sedimentary strata into three main fossiliferous intervals each exposed at one of the three main areas: Gafura, Seraitu, and Uraitele. Alemseged et al. designate these as informal stratigraphic units, with the aim of formalising a regional lithostratigraphic terminology in future work, building on these presently informal terminologies.

The lowest stratigraphic unit, Gafura, begins with a sequence of thick, columnar-jointed basalt flows with intra-flow residual paleosols developed on the basalts. The Gafura sediments are poorly exposed, but occur along the southwestern flank of Iki-Ilu Ridge, and are best represented by a section exposed at Sidiha Koma (section JGW15-1). The upper surface of the basalt flow at the base of this zone forms a broad low-lying surface, dissected by the Gafura River, extending into the base of the Daamé Valley. This sequence of basalts defines the Gafura Basalts-I and Gafura Basalts-II groups it underlies the main sedimentary sequence and is thus stratigraphically distinct from the overlying flows represented as the Afar Stratoid Series. Within the lowermost exposures of the Gafura Basalts, a normal to reverse magnetostratigraphic reversal is recorded Given the age constraints of overlying strata, this reversal must be equal to or older than the age of the base of the Kaena Chron (3.127 million years).

The transition to overlying sediments of the Sidiha Koma area is marked by mudstones with ferruginised burrows interspersed with thin, poorly-sorted sands with a framework of basaltic lithic grains, occasionally containing abundant Gastropods, and some Bivalves. Near the top of Gafura sediments, additional basalt flows overlie the sediments locally, although these have not yet been attributed to one of the geochemically-defined groups. The fossiliferous sediments of Gafura underlie a widespread diatomaceous unit, the Iki-Ilu Diatomite, which can be mapped in regionally extensive exposures along the southwestern flank of Iki-Ilu Ridge, across its southern tip, and into the floor of the Seraitu Valley, making this a practical stratigraphic boundary. The Hinti Mageta Tuff (2.914 million years old), preserved within the Iki-Ilu Diatomite, provides an upper age limit to the Gafura sediments.

The middle stratigraphic unit is represented by the Seraitu lake beds, which often form bare, steep cliffs of largely mudstone outcrops representing lacustrine deposition. Alemseged et al. use the base of the Iki-Ilu Diatomite as the lower boundary of this zone, although most sections cannot be mapped in continuity within a measured stratigraphic distance to the diatomite. The upper boundary of this zone may not be defined by a single widespread marker but can be locally taken as the stratigraphically lowest basalt flow with chemical composition characteristic of the Uraitele-Garsele Dora Group, which may consist of several different flow units. The Uraitele-Garsele Dora Group is frequently accompanied by an overlying, distinctive and widespread air-fall tuff with well-preserved glass and small lapilli-sized pumices, the Goyana Tuff. Thus, the presence of one or both of these markers provides a working stratigraphic definition.

The sediments of the Seraitu lake beds are predominantly laminated clays which often contain abundant Ostracods, Gastropods and some Bivalves, as well as plant fragments and Fish remains. Diatoms in the Iki-Ilu Diatomite are somewhat recrystallised but identifiable to the genus Aulacoseira. Tephras are also numerous in the lake beds but characteristically thin (less than 30 cm), often air-fall occurrences, in which the primary glass is altered. Despite this, abundant feldspar crystal populations are preserved, providing two of the Argon⁴⁰/Argon³⁹ dates reported by Alemseged et al.. Besides the Hinti Mageta Tuff at the base of the Seraitu lake beds, two tuffs within the lake sediments provide precise ages: MLP14/SR-6 at 2.576 million years ago and MLP14/GOY-2 at 2.485 million years ago. In addition to the chronological information from these markers, two sections within the Seraitu lake beds zone record a magnetostratigraphic reversal which we interpret to be the Gauss/Matuyama, dated to 2.59 million years ago.

The third unit, Uraitele, includes limited sedimentary exposures in-between extensive and thick basalt flows of the Uraitele-Garsele Dora Group, Gafura Basalts-I, and Gafura Basalts-II groups, which outcrop in the Goyana and Uraitele areas. The sediments include some lenticular sandstones interpreted as fluvial channels, but are predominantly laminated mudstones with occasional Gastropod and Bivalve bearing sandstones formed on surfaces of the Uraitele-Garsele Dora Group basalt or within the mudstones. The upper boundary of the Uraitele zone is as yet undefined, as the section continues in a thick sequence of numerous basalt flows that extend into the ridges of the Magenta Mountains at the northern extent of the area (mapped as the Afar Stratoid Series). The uppermost flows form two chemically-distinct groups, termed the Gafura Basalts-I and Gafura Basalts-II groups.

As with the Gafura area, the sediments of the Uraitele area contain a number of reworked vitric tuffs generally lacking large feldspar populations, but having distinctive chemical composition with no known correlates from the Awash Valley. One of these vitric tephras, the Uraitele Tuff, has also produced populations of feldspars suitable for dating, and represents the most precise age of those presently analysed from the Mille-Logya area: 2.443 million years old.

Given the above stratigraphic sequence, Alemseged et al. make some important interpretations of the basin’s history. Prior to about 3 million years ago, there is no evidence of an active depositional basin in the Mille-Logya region. Thus, during the period characteristic of most active lacustrine sedimentation at Hadar and Dikika (about 3.6𔃁 million years old), the sequence of Gafura Basalts and residual palaeosols at Mille-Logya suggests subaerial emplacement of basaltic lavas followed by periods of non-deposition and pedogenesis. The local onset of active subsidence and sedimentation is marked by early onset of shoreline and shallow lacustrine deposits overlying the uppermost Gafura Basalts-II Group. The subsequent lacustrine sequence culminates in a deep, well-mixed lake represented by an Aulacoseira-dominated Diatom facies within the Iki-Ilu Diatomite and invertebrate fossil rich mudstones preserved throughout the Seraitu lake beds zone. Few terrestrial indicators are present except occasional coarser-grained facies suggestive of shorelines or brief subaerial exposure, where occasional rhizoliths are preserved and Vertebrate fossils are slightly more common. This lacustrine setting is persistent throughout the exposures and continues into the overlying Uraitele sediments, the lowermost of which are characterised by gastropod-bearing shoreline facies developed on the surface of basalt flows. Ultimately, the lacustrine phase ends with thin intervening sediments between basalt flows of the Gafura Basalts Group, which have been associated with the fissural system of the axial rift.

An archaeological survey was conducted in conjunction with palaeontological reconnaissance. Archaeological visibility is extremely low due to the combination of a thick colluvial cover, relatively few exposed sections and the fact that most of the sedimentary deposits are lacustrine in origin. Nevertheless, all of the fossiliferous localities and their surroundings were examined on multiple occasions. In general, lithic artifacts are infrequent and scattered at very low density. The only exception comes from Seraitu Dida where slopes on two adjacent ridges with sediments above the Uraitele Tuff have numerous handaxes and Levallois cores and flakes made on a fairly consistent coarse-grained but good quality volcanic material. While artifact densities were relatively high in this area, no concentrations suggested a source for this material that has temporal constraint. Nevertheless, Alemseged et al. excavated three trenches at the crest of one of the ridges above the Uraitele Tuff. In one of these trenches, about one meter into a layer of gravel, they found a single Levallois flake. A maximum age is provided by the Uraitele Tuff (2.443 million years old) but the minimum age remains unconstrained. Archaeological exploration will continue.

The stratigraphic setting provides a framework to interpret fossil data recovered from the three units. Fossil concentrations at Mille-Logya are sparse and relatively difficult to locate. Yet, after four field seasons, the fossil collection currently includes 2287 specimens, of which 1835 were collected while the rest were observed and documented on site Fossil collections at the Mille-Logya Project followed a standardised protocol in order to minimize collection bias. The identifiable specimens comprise 62 Cercopithecidae, 4 Hominidae, 33 Proboscidea, 10 Camelidae, 165 Suidae, 135 Hippopotamidae, 36 Giraffidae, 944 Bovidae, 218 Equidae, 21 Rhinocerotidae, 20 Carnivora, 17 Birds, and some Rodents, Fish, Turtles, and Crocodiles.

Hominins were recovered from four different localities and are represented by a left and right proximal ulnae (MLP-786 & MLP-1617 respectively: 2.6𔃀.8 million years old from two different localities, thus not from the same individual), a calvarium fragment (MLP-1469: 2.6𔃀.8 million years old) and a diagnostic and complete upper second molar crown (MLP-1549: 2.4𔃀.5 million years old). The molar, found in two pieces that refit cleanly, measures 14 mm and 12.5 mm buccolingually and mesiodistally, respectively, falling within the known range of Australopithecus afarensis as well as early Homo as represented by A.L. 666-1 from the younger horizons at Hadar dated at 2.33 million years old. The buccolingual and mesiodistal dimensions overlap with those of early Homo and are closest to the mean values. The occlusal outline, which is dominated by the two mesial cusps, is rhomboidal with the longest axis running from the distolingual to mesiobuccal corners. The distobuccal corner is truncated. The tooth is moderately worn with no cuspal dentine exposure. The lingual wear flattens the protocone and hypocone and polishes the lingual margin leading to a rather homogenised region of the lingual half of the tooth. In contrast, the paracone and metacone are not as worn and the buccal margin is still sharp. The distal marginal ridge and distal fovea are quite perceptible, but the mesial marginal ridge is largely worn down leaving only a hint of the mesial fovea. In occlusal view, running buccal to the protocone and distal to the paracone is a large buccal groove that dominates other grooves and is positioned mesiobuccal to a lingual groove that is much smaller.

An asymmetric and rhomboidal occlusal outline of the upper second molar has been reported to characterise Homo erectus and Homo habilis but is rare in Australopithecus afarensis. The Mille-Logya Project M2 possesses these features but is buccolingually broad unlike Homo erectus. Based on size and average enamel thickness in addition to diagnostic occlusal features, Alemseged et al. attribute it to Homo sp. With an age of 2.4𔃀.5 million years, this molar represents one of the oldest specimens of this genus and expands the earliest Homo sample from the Afar, which currently includes only LD 350-1 from Ledi Geraru at 2.8 million years and A.L. 666-1 from Hadar at 2.33 million years.

The calvarium fragment is probably from the parietal the bone is relatively thin and different from what is seen in middle Pleistocene specimens such as Bodo. MLP-1617 and MLP-786 are fragmentary proximal ulnae mainly preserving the olecranon and the trochlear notch. The two specimens differ in size and degree of preservation. While MLP-786 is larger, MLP-1617 is better preserved, especially its trochlear notch where the maximum mediolateral breadth, including the radial notch, is about 28 mm. In MLP-786, most of the distal aspect of the trochlear notch including the radial notch is broken away. In both, various quadrants of the trochlear notch are mildly concave. Maximum radial notch dimensions are 13.4mm anteroposteriorly and 9.4 mm superoinferiorly in MLP-1617. In both specimens, the olecranon process is moderately projected proximally and slightly more pronounced in MLP-786, as is seen in other Hominins. The olecranon proximodistal height is 7.3mm and 8.6mm respectively and similar to that of A.L. 438-1 (Australopithecus afarensis). The trochlear keel is mild in MLP-1617 and not perceptible in MLP-786. Posteriorly, MLP-1617 and MLP-786 measure 15.3mm and 18.5 mm, respectively at the middle of the trochlear notch and proximally they measure 20.8mm and 23.6 mm. The two ulnae can readily be assigned to Hominini based on the extent of the olecranon process and the orientation and extent of the trochlear and radial notches. Many features and dimensions discussed by Michelle Drapeau to characterise most fossil Hominins are preserved (mainly in MLP-1617) but further discrimination is not possible and these bones are therefore attributed to Hominini indet.

Cercopithecines, especially Theropithecus, are abundant though mostly represented by fragmentary teeth and extremities of postcranials. The Mille-Logya Project Theropithecus is characterised by diagnostic high crowned, bilophodont molars with deeply incised notches and clefts. Based on limited existing material, molar size appears larger than in representatives of Theropithecus oswaldi from the older members of the Hadar Formation. Some teeth displaying similar features are smaller we interpret them as females of the same species. There are also several teeth that do not display these diagnostic Theropithecus features, which Alemseged et al. assign to Cercopithecinae indet. pending recovery of more complete specimens.

Enamel fragments belonging to Deinotherium are frequently encountered, and a nearly complete skull was excavated at Uraitele. Dental elements and postcranials of Elephantidae are common as well, and some were collected a complete M3 from Uraitele best matches Elephas recki shungurensis known from Omo Shungura Members C to F, but there are no clear boundaries between successive subspecies to allow more precise biochronological attribution.

A single mandibular fragment belongs to an Aardvark (Orycteropus).

The family Camelidae is extremely rare in the East African Plio-Pleistocene, and the discovery of ten specimens at Mille-Logya is remarkable. One of them is the only partial skull known from this part of Africa to date and detailed analysis of this skull has been published elsewhere.

Though remains of Hippopotamidae are common throughout the sequence, there is only one species it has a hexaprotodont dentition, with a slightly smaller i2 than i1 and i3, thus resembling early forms of the ‘aff. Hippopotamus protamphibius'. It is clearly different from Hexaprotodon bruneti, from the Hata Member of the Bouri Formation at about 2.5 million years old, which has a very large i3. Yet, formal identification must await the revision of the Turkana and Hadar material. No Tetraprotodont dentition has been recovered from the Mille-Logya Project area.

Notochoerus is the most common genus of Suid. Several complete third molars, mostly from the Gafura unit, are smaller than those of Notochoerus scotti from Omo C and later members, and match those of Notochoerus euilus from Omo B or the Hadar Formation. The morphology and mesiodistal length of their molars are similar to those in Notochoerus clarki, which coexists with Notochoerus scotti at Omo, but are broader and Alemseged et al. attribute them to Notochoerus euilus. Kolpochoerus is less common and all specimens are of comparable size. Dimensions of the third molars, mostly from the Seraitu lake beds, are close to the upper end of the range for Kolpochoerus afarensis from the Hadar Formation, or to the lower end of the range for Kolpochoerus limnetes from Shungura D-E, and are closest to specimens from Shungura B and C. They are also somewhat larger than those of Kolpochoerus philippi, from Matabaietu at about 2.5 million years old. There is no definite evidence of Nyanzachoerus, nor of Metridiochoerus.

Both Giraffa and Sivatherium are represented, but are rare. The relatively more common Giraffa is not particularly large, and a second, smaller species (Giraffa cf. gracilis) is also present.

Bovids are by far the most common Mammals, and almost half of the identifiable specimens, mostly represented by teeth, belong to Alcelaphini. They are followed in decreasing order of abundance by the Reduncini, Bovini, Aepycerotini, Antilopini, and Tragelaphini. Horn-cores are encountered relatively frequently, but are seldom associated with other cranial parts. An Alcelaphin that resembles Damaliscus ademassui from Gamedah dated to about 2.5 million years and perhaps a primitive Wildebeest (Connochaetes sp.) are present at Uraitele. Alemseged et al. assign the most common Alcelaphin to Damalborea, a genus that is present throughout the Hadar Formation. Although variation at Hadar is great, the Mille-Logya Project form is distinctive in its short, twisted horn-cores with homonymous torsion. It could be an evolved form of Damalborea grayi from the Denen Dora Member at Hadar. An unidentified, very small Alcelaphin is reminiscent of the one that first appears in the Kada Hadar 2 submember. There are at least two species of Reduncins. The less common one is probably Kobus sigmoidalis, best known from the Turkana basin and recently reported from Ledi-Geraru. he specific identity of the more common reduncin is not clear it resembles Kobus oricornus from Omo Shungura, West Turkana, Koobi Fora, and Hadar. Surprisingly, this taxon is absent in the nearby Ledi-Geraru. A Bovini horn-core from the middle part of the section is comparable to the type of Pelorovis kaisensis, from Kaiso village in Uganda, about 2.5 million years old. Aepyceros is common but species identification is difficult due to incompleteness. One of the horncores is larger than those from the Kada Hadar Member. Gazella, the only Antilopin so far recovered, is represented by several long and slender horn-cores resembling Gazella harmonae from the Kada Hadar Member at Hadar, and probably Omo Shungura Member F and Olduvai Bed I. Most Tragelaphin horn-cores are from the younger part of the exposures and resemble Tragelaphus nakuae in their moderate torsion and in the presence of a low supraoccipital ridge of braincase. A very long horn-core is reminiscent of a specimen from Omo-160 in Shungura Member C. Overall, the Tragelaphin material suggests an age of 2.6𔃀.3 mullion years. A second and rare species from the middle part of the sequence is similar to Tragelaphus gaudryi of which an ancestral form appears in Omo Shungura Member C.

Though Rhinos are rare at the Mille-Logya Project, both the grazer Ceratotherium and the browser (or mixed-feeder) Diceros are encountered.

Equids are fragmentary but quite common. Alemseged et al. tentatively attribute all remains to a single species of Hipparion. A complete set of upper incisors shows that the I3 is not reduced, and the lingual grooves are shallow, in contrast to what is seen in derived hipparions of the cornelianus group. A remarkable feature is the absence or poor development of the ectostylid on many lower teeth. A moderately worn and well-preserved set of molars shows no ectostylids at all. Postcranial dimensions are close to the lower end of the Hadar range where skulls show that at least two species are represented.

Some postcranials potentially representing multiple taxa belong to Hyaenidae. Two metapodials and a tooth belong to a Felid, cf. Dinofelis. In addition, a distal radius belongs to a Servalsised Felid.

Antoine Louchart identified a large Ostrich and a member of the Anatidae, perhaps Sarkidiornis melanotos or Plectropterus gambensis. Large Ostriches have been mentioned from a number of Pleistocene Old World sites they are likely attributable to Struthio asiaticus.

Crocodile teeth are widespread, and a few specimens represent Euthecodon.

Kathlyn Stewart identified Bagrid and Clariid Fish.

The Hadar Formation fauna, documented in the nearby sites of Hadar, Dikika, and Ledi-Geraru, has been widely studied and offers a very good reference for the new material from Mille-Logya. The Mille-Logya fauna points to a generally younger, late Pliocene age but shares a number of taxa with those from the Hadar Formation, where many have a wide chronological range. Of biochronological significance are the Antelopes, Damalborea and Kobus cf. oricornus. Gazella harmonae is also shared with Hadar, although this species has wide chronological and geographic ranges. Another indicator of a similar age is the Hexaprotodont Hippopotamid, present in the middle part of the sequence at Mille-Logya. The Suids also fall largely within the size range seen in the Hadar Formation, but most diagnostic specimens are encountered in the lower and middle parts of the sequence. It should be noted, however, that Kolpochoerus from the Seraitu lake beds is more consistent with the older absolute ages of this unit than with the younger ones. The absence of Nyanzachoerus suggests that the Mille-Logya Project assemblage postdates most of the fauna from Hadar. Although the above is generally true, there are differences within the Mille-Logya fauna indicating that sites in the southern portion of the research area are older than those in the north.

As in most African Pliocene sites, Bovids are the most common group followed by Equids and Suids. Primates are fairly common but rare compared to those at Hadar and Dikika. One striking feature of the Mille-Logya fauna is the high prevalence of Equids, particularly relative to Suids. At Hadar and Dikika the reverse is consistently the case. While this is true when the whole Mille-Logya assemblage is considered as a unit, looking at the different horizons reveals a different pattern. Gafura (roughly 2.9 to 2.8 million years old) contains fauna that is similar to that of Hadar where the proportion of Bovids compared to Suids and Equids is not very high and also where Suids are more common than Equids. In contrast, the Seraitu lake beds (roughly 2.8 to 2.6 million years old ) and Uraitele zone (roughly 2.5 to 2.4 million years old ) contain more Bovids while Equids overtake Suids. This suggest that the older fauna in Gafura might have followed the migration of the Hadar Lake Basin northeast around 3 million years ago , resulting in faunal similarities with Hadar. Relative faunal abundance however seems to have been altered in the younger horizons of the Seraitu lake beds and Uraitele (after abou 2.9 million years ago ), leading to a faunal assemblage indicative of more open conditions. This is supported by the overall abundance of Bovids, particularly Alcelaphins, and Equids probably indicating an in situ faunal turnover.

Alemseged et al. used all Mille-Logya Project specimens identifiable to genus to compute the Sørenson (also known as Dice) faunal dissimilarity index for each pairwise comparison among the faunal zones. The results indicate that Seraitu and Uraitele are more compositionally similar to one another at the genus level than either of these zones is to Gafura. Alemseged et al. further conducted a correspondence analysis on taxon abundances in order to compare the Mille-Logya Project faunal zones with assemblages from the Hadar Formation at Hadar and Dikika. They restricted their analysis to seven bovid tribes (Aepycerotini, Alcelaphini, Antilopini, Bovini, Hippotragini, Reduncini, Tragelaphini), the Suid genera Notochoerus and Kolpochoerus, and all Equidae identified only to family. These relatively broad taxonomic categories were chosen to reduce the influence of inter-observer variation in taxonomic identifications. The correspondence analysis demonstrates that the Gafura assemblage is distinct from the Seraitu and Uraitele assemblages, with Gafura showing a high abundance of Notochoerus, and the Seraitu and Uraitele assemblages showing a high abundance of Alcelaphini and Antilopini, which are open-habitat indicator taxa.

It is possible that some of the observed taxonomic differences between the collecting areas of successive ages are due to small sample size, but some have clear biochronological significance. Alemseged et al. interpret the presence of Damaliscus cf. ademassui, Connochaetes sp., and perhaps Kobus sigmoidalis, at Uraitele to suggest that the latter is younger than Gafura and Seraitu. In addition, it is not yet certain if the Tragelaphus from Gafura is a 'typical' Tragelaphus nakuae, and whether Damalborea survived into the Uraitele horizon.

In sum, the overall similarity of the Mille-Logya fauna, especially from the older Gafura sites, with that from the Hadar Formation is remarkable. Also, in spite of the apparent younger age, it contrasts with younger sites in the Middle and Lower Awash. For instance, the Bovid assemblage of Bouri Hata at about 2.5 million years before present includes a long list of Bovid taxa for which there is no evidence at Mille-Logya: Beatragus, cf. Numidocapra, cf. Rabaticeras, Megalotragus, Hippotragus, Oryx, and Tragelaphus strepsiceros. The nearby Ledi-Geraru area contains sediments whose ages are very similar to those of Mille-Logya, but their faunal assemblage also looks different, containing Beatragus, Syncerus and Ugandax, but lacking Kobus oricornus, the most common Reduncini at Mille-Logya.

In regards to palaeoenvironments, Tragelaphins are rare as are Giraffes, while hipparions and reduncins are common. Alcelaphins are by far the most abundant Bovids. The relative abundance of the otherwise rare Camelus is also noteworthy. On the whole, this assemblage points to an open savanna or grassland with little woody cover. This in conjunction with the presence of Homo at Mille-Logya may suggest that the earliest members of Homo were associated with more open environments than Australopithecus was. The in situ faunal change at Mille-Logya may be linked to environmental and climatic factors that may have also caused Homo to emerge in or disperse to the region. Further field work and faunal analysis with better taxonomic resolution and use of additional proxies will help to better elucidate the palaeoenvironmental and palaeoecological conditions of this new site and its relevance to the understanding our origins.

Although the Afar Depression has contributed uniquely to our understanding of the biological and cultural evolution of Hominins and faunal evolution more broadly over the past 6 million years, palaeontological data have been sparse in the region from the stratigraphic time interval (2.9𔃀.4 million years ago) represented by the Mille-Logya sediments. Alemseged et al.'s work shows the unique nature of the faunal assemblage and composition at the new site. The results suggest a northeast migration of the Hadar Basin and the creation of a new depocenter at Mille-Logya with continuity of the lake deposits and shoreline sediments that preserve a fauna similar to that from Hadar. Furthermore, Alemseged et al. have identified three different fossiliferous units in this project area suggesting an in situ faunal change. Yet, relative to the Hadar Formation fauna, which is older than 3 million years, Mille-Logya has a large proportion of Alcelaphin Bovids and Equids, indicating that the area likely included more open habitats after 3 million years ago. The absence of early Metridiochoerus, Menelikia and Australopithecus from Mille-Logya suggests that these habitats may not have been suitable for these taxa. The presence of Homo is instead suggestive of an adaptive shift in the transition between Australopithecus and Homo to settings with overall drier and more open conditions.

Looking forward, more research at Mille-Logya Projest will allow better documentation of the geological setting and palaeontological content of the poorly known post-Hadar-Dikika periods to better articulate the environmental setting of Human evolution. For the first time, Alemseged et al. now have a better understanding of the cause for local cessation of sedimentation in the Hadar-Dikika areas after approximately 2.9 million years ago. The new data set will serve as the basis for within-site faunal comparison and for testing competing spatial and temporal faunal and environmental change hypotheses. The presence of Hominin remains, including Homo associated with a diverse fauna presents a unique opportunity to address key questions that pertain to our genus and factors that led to its emergence and subsequent biological and cultural evolution.

List of fossil sites

This list of fossil sites is a worldwide list of localities known well for the presence of fossils. Some entries in this list are notable for a single, unique find, while others are notable for the large number of fossils found there. Many of the entries in this list are considered Lagerstätten (sedimentary deposits that exhibits extraordinary fossils with exceptional preservation—sometimes including preserved soft tissues). Lagerstätten are indicated by a note ( [Note 1] ) in the noteworthiness column.

Fossils may be found either associated with a geological formation or at a single geographic site. Geological formations consist of rock that was deposited during a specific period of time. They usually extend for large areas, and sometimes there are different important sites in which the same formation is exposed. Such sites may have separate entries if they are considered to be more notable than the formation as a whole. In contrast, extensive formations associated with large areas may be equivalently represented at many locations. Such formations may be listed either without a site, with a site or sites that represent the type locality, or with multiple sites of note. When a type locality is listed as the site for a formation with many good outcrops, the site is flagged with a note ( [Note 2] ). When a particular site of note is listed for an extensive fossil-bearing formation, but that site is somehow atypical, it is also flagged with a note ( [Note 3] ).

Many formations are for all practical purposes only studied at a single site, and may not even be named. For example, sites associated with hominin, particularly caves, are frequently not identified with a named geologic formation. Therefore, some sites are listed without an associated formation.


Sedimentary basins in eastern Africa preserve a record of continental rifting and contain important fossil assemblages for interpreting hominin evolution. However, the record of hominin evolution between 3 and 2.5 million years ago (Ma) is poorly documented in surface outcrops, particularly in Afar, Ethiopia. Here we present the discovery of a 2.84–to 2.58–million-year-old fossil and hominin-bearing sediments in the Ledi-Geraru research area of Afar, Ethiopia, that have produced the earliest record of the genus Homo. Vertebrate fossils record a faunal turnover indicative of more open and probably arid habitats than those reconstructed earlier in this region, which is in broad agreement with hypotheses addressing the role of environmental forcing in hominin evolution at this time. Geological analyses constrain depositional and structural models of Afar and date the LD 350-1 Homo mandible to 2.80 to 2.75 Ma.

Skull scans reveal evolutionary secrets of fossil brains

Scientists have long been able to measure and analyze the fossil skulls of our ancient ancestors to estimate brain volume and growth. The question of how these ancient brains compare to modern human brains and the brains of our closest primate cousin, the chimpanzee, continues to be a major target of investigation.

A new study published in Science Advances used CT-scanning technology to view 3-million-year-old brain imprints inside fossil skulls of the species Australopithecus afarensis (famous for “Lucy” and “Selam” from Ethiopia’s Afar region) to shed new light on the evolution of brain organization and growth.

The research reveals that while Lucy’s species had an ape-like brain structure, the brain took longer to reach adult size, suggesting that infants may have had a longer dependence on caregivers, a human-like trait.

The CT-scanning enabled the researchers to get at two long-standing questions that could not be answered by visual observation and measurement alone: Is there evidence for human-like brain reorganization in Australopithecus afarensis, and was the pattern of brain growth in this species more similar to that of chimpanzees or that of humans?

Brain imprints in fossil skulls of the species Australopithecus afarensis (famous for “Lucy” and the “Dikika child” from Ethiopia, pictured here) shed new light on the evolution of brain growth and organization. The exceptionally preserved endocranial imprint of the Dikika child reveals an ape-like brain organization, and no features derived toward humans. Credit: Philipp Gunz, MPI EVA Leipzig.

To study brain growth and organization in A. afarensis, the researchers, including Arizona State University paleoanthropologist William Kimbel, scanned eight fossil crania from the Ethiopian sites of Dikika and Hadar using high-resolution conventional and synchrotron-computed tomography. Kimbel, leader of the field work at Hadar, is director of the Institute of Human Origins and Virginia M. Ullman Professor of Natural History and the Environment in the School of Human Evolution and Social Change.

Lucy’s species inhabited eastern Africa more than three million years ago — “Lucy” herself is estimated to be 3.2 million years old — and occupies a key position in the hominin family tree, as it is widely accepted to be ancestral to all later hominins, including the lineage leading to modern humans.

“Lucy and her kin provide important evidence about early hominin behavior — they walked upright, had brains that were around 20% larger than those of chimpanzees, and may have used sharp stone tools,” said coauthor Zeresenay Alemseged from the University of Chicago, who directs the Dikika field project in Ethiopia and is an international research affiliate with the Institute of Human Origins.

Brains do not fossilize, but as the brain grows and expands before and after birth, the tissues surrounding its outer layer leave an imprint on the inside of the bony braincase. The brains of modern humans are not only much larger than those of our closest living ape relatives, but are also organized differently and take longer to grow and mature.

Compared with chimpanzees, modern human infants learn longer and are entirely dependent on parental care for longer periods of time. Together, these characteristics are important for human cognition and social behavior, but their evolutionary origins remain unclear.

The CT scans resulted in high-resolution digital “endocasts” of the interior of the skulls, where the anatomical structure of the brains could be visualized and analyzed. Based on these endocasts, the researchers could measure brain volume and infer key aspects of cerebral organization from impressions of the brain’s structure.

A key difference between apes and humans involves the organization of the brain’s parietal lobe — important in the integration and processing of sensory information — and occipital lobe in the visual center at the rear of the brain.

The exceptionally preserved endocast of “Selam,” a skull and associated skeleton of an Australopithecus afarensis infant found at Dikika in 2000, has an unambiguous impression of the lunate sulcus — a fissure in the occipital lobe marking the boundary of the visual area that is more prominent and located more forward in apes than in humans — in an ape-like position.

The scan of the endocranial imprint of an adult A. afarensis fossil from Hadar ( early hominid AL 162–28) reveals a previously undetected impression of the lunate sulcus, which is also in an ape-like position.

Brains do not fossilize, but as the brain grows, the tissues surrounding its outer layer leave an imprint in the bony braincase. The Dikika child’s endocranial imprint reveals an ape-like brain organization, and no features derived toward humans. Credit: Philipp Gunz, MPI EVA Leipzig.

Some scientists had conjectured that human-like brain reorganization in australopiths was linked to behaviors that were more complex than those of their great ape relatives (e.g., stone-tool manufacture, mentalizing and vocal communication). Unfortunately, the lunate sulcus typically does not reproduce well on endocasts, so there was unresolved controversy about its position in Australopithecus.

“A highlight of our work is how cutting-edge technology can clear up long-standing debates about these three million-year-old fossils,” co-author Kimbel said. “Our ability to ‘peer’ into the hidden details of bone and tooth structure with CT scans has truly revolutionized the science of our origins.”

A comparison of infant and adult endocranial volumes also indicates more human-like protracted brain growth in Australopithecus afarensis , likely critical for the evolution of a long period of childhood learning in hominins.

In infants, CT scans of the dentition make it possible to determine an individual’s age at death by counting dental growth lines. Similar to the growth rings of a tree, virtual sections of a tooth reveal incremental growth lines reflecting the body’s internal rhythm. Studying the fossilized teeth of the Dikika infant, the team’s dental experts calculated an age at death of 2.4 years.

The pace of dental development of the Dikika infant was broadly comparable to that of chimpanzees, and therefore faster than in modern humans. But given that the brains of Australopithecus afarensis adults were roughly 20% larger than those of chimpanzees, the Dikika child’s small endocranial volume suggests a prolonged period of brain development relative to chimpanzees.

“The combination of ape-like brain structure and human-like protracted brain growth in Lucy’s species was unexpected,” Kimbel said. “That finding supports the idea that human brain evolution was very much a piecemeal affair, with extended brain growth appearing before the origin of our own genus, Homo.”

Among primates, different rates of growth and maturation are associated with different infant-care strategies, suggesting that the extended period of brain growth in Australopithecus afarensis may have been linked to a long dependence on caregivers. Alternatively, slow brain growth could also primarily represent a way to spread the energetic requirements of dependent offspring over many years in environments where food is not always abundant.

In either case, protracted brain growth in Australopithecus afarensis provided the basis for subsequent evolution of the brain and social behavior in hominins, and was likely critical for the evolution of a long period of childhood learning.

Research article: Australopithecus afarensis endocasts suggest ape-like brain organization and prolonged brain growth. Science Advances. Philipp Gunz. Simon Neubauer, Dean Falk, Paul Tafforeau, Adelube Le Cabec, Tanya M. Smith, William H. Kimbel, Fred Spoor, Zeresenay Alemseged.

Top video: Brain imprints in fossil skulls of the species Australopithecus afarensis (famous for “Lucy” and the “Dikika child” from Ethiopia pictured here) shed new light on the evolution of brain growth and organization. Several years of painstaking fossil reconstruction and counting of dental growth lines yielded an exceptionally preserved brain imprint of the Dikika child and a precise age at death. These data suggest that Australopithecus afarensis had an ape-like brain and prolonged brain growth. Credit: Philipp Gunz, MPI EVA Leipzig

Pliocene Hominin Diversity, Sympatry, and the Question of Niche Partitioning

From the onset of the study of human origins as a scientific field, environmental and climatic changes have been posited as the driving force behind the origin, extinction, and adaptive events of the human lineage (e.g., refs. 68 ⇓ ⇓ ⇓ –72), which has had significant impact on the formulation of hypotheses regarding the evolution of hominins, particularly on the questions of taxonomic diversity and habitat preferences. The idea that two related hominin species could not have been sympatric because of overlapping resource requirements and preferences is one of the driving forces of the single species hypothesis (73). However, fossil discoveries in the 1970s and 1980s challenged this by clearly demonstrating the coexistence of Paranthropus and Homo, in some cases in close proximity, during the Pleistocene (74 ⇓ –76). Hominin fossil discoveries since the 1990s are now showing that hominin diversity was not limited to the Pleistocene but rather extended as far back as the middle Pliocene, if not earlier. The Pliocene hominin fossil record reviewed above, particularly from the time between 3.8 Ma and 3.0 Ma, indicates not only broad sympatry (two or more species occurring over the same region), but also direct sympatry (co-occurrence of two or more species in the same immediate area) of middle Pliocene hominins.

Taxonomic diversification and coexistence of multiple large-bodied Miocene hominoids are well documented in the Cenozoic fossil record (77). There is adequate fossil evidence to show that multiple hominin taxa coexisted during the Pleistocene. The contemporaneous presence of multiple closely related taxa has also been documented among nonhominoid primates (78 ⇓ ⇓ –81) and other mammalian taxa, such as bovids (82), throughout the Plio-Pleistocene. It would not be surprising, then, if hominins were as diverse at any given time in their evolutionary history, but identifying the dynamics that triggered such diversification among these relatively large-bodied hominins during the middle Pliocene and other geological times would be of paramount importance. It has been posited that the most probable explanation for diversification within any sympatric group of primates regardless of body size is niche partitioning, where each taxon develops a specific foraging strategy and exploits unique dietary resources (e.g., refs. 83 and 84). It has been shown, however, that stable coexistence among related taxa does not always require resource specialization (85), and recent studies of extant faunal communities suggest that predation pressures reduce competition in secondary consumers and promote taxonomic diversity and coexistence (86).

At Woranso-Mille, Au. afarensis and Au. deyiremeda appear to have been living in direct sympatry with each other. Thus, questions regarding how they are able to coexist and share the landscape immediately arise. Both species appeared to have broad dietary requirements (e.g., refs. 87 ⇓ ⇓ ⇓ –91), suggesting that they could have been ecological generalists (i.e., broad use of resources and high tolerance of environmental change) (92). Modern chimpanzees and gorillas are broadly sympatric across equatorial Africa and share the same habitat in many areas (93). These two closely related species have significant overlap in their dietary pattern and resource use, but differ significantly in their use of fallback foods and food-harvesting strategies. Whereas both species appear to focus on fruit as their primary, preferred food, gorillas are willing to consume herbaceous vegetation when their preferred food item is unavailable chimpanzees, on the other hand, broaden their home range to harvest their preferred food and do not use herbaceous vegetation as their fallback food (93 ⇓ ⇓ –96). It is possible that, analogous to modern chimpanzees and gorillas, one of the two Australopithecus species at Woranso-Mille had greater ecological niche breadth, or they may have specialized in different fallback foods during times of preferred food scarcity, while sharing the same resources when preferred food items are abundant.

With increasing fossil evidence, it is possible to begin to put forth hypotheses on the ecological strategies of Australopithecus as a clade. The association of Au. afarensis with different habitat types throughout its geographic and temporal range has suggested to many workers that it was a generalist with broad habitat tolerances (97 ⇓ ⇓ ⇓ ⇓ –102). Although we do not have the same level of paleohabitat resolution for all of the other Pliocene hominin species, available evidence suggests that they are similarly associated with a wide range of habitat types from savanna-like grassland to an array of habitats with significant woodland components (103 ⇓ ⇓ –106). Based on what we currently know of the paleohabitats of Pliocene Australopithecus species (97 ⇓ ⇓ ⇓ ⇓ ⇓ ⇓ ⇓ ⇓ –106) and their dietary adaptations (62 ⇓ ⇓ –65, 87 ⇓ ⇓ ⇓ –91, 107 ⇓ –109), it is not unreasonable to put forth a null hypothesis that posits Australopithecus was a eurytopic, or generalist, clade.

Eurytopic groups are predicted to have broad dietary breadth, wide habitat preferences, low species diversity, long species duration, and absence or rare sympatry of sister species, among other variables (110 ⇓ –112 see ref. 112 for complete list and discussion). Although some Australopithecus species are younger than the time period reviewed here, they are all considered here for the purposes of this discussion. Species of Australopithecus generally have broad diets based on enamel carbon isotopic studies (63, 87, 91, 104, 107, 108), with the exception of Au. anamensis (62) and the much younger Au. sediba (109). There also does not appear to be strong habitat preference for the genus, with reconstructions of mosaic habitats for most of the Australopithecus sites (99, 101, 102), although it is unclear how the hominins were using the landscape. With six species currently referred to Australopithecus, even though this genus is considered as paraphyletic by some researchers (58, 67, 113), it would appear that it is relatively speciose. However, it is difficult to assess how long-lived each of these species might have been, or how many of them overlapped in time and space, and therefore difficult to make sound arguments about sympatry and niche partitioning among these species. However, most Australopithecus species appear to have been allopatric, except for Au. afarensis, which appears to have been sympatric with Au. deyiremeda at Woranso-Mille (25). Given the dietary breadth, diverse habitats, uncertainty of first and last appearance dates, and the rarity of sympatry (of at least five sites where Au. afarensis occur, only one site shows evidence of sympatry), the posited hypothesis cannot be rejected. If Australopithecus was indeed an eurytopic clade, as the currently available evidence suggests (101), then this has profound implications for how we understand its mode and rate of evolution generalist clades, given their adaptability, have low rates of speciation and extinction (110, 112). However, only with more fossil evidence can we confidently reject or accept the hypothesis that Australopithecus was eurytopic. It is important to note that niche partitioning may not be the only means for multiple species within a genus to share the same habitat, as foraging strategies (93), type and quantity of resources (93), and predation pressure (86), can impact taxonomic diversity and the coexistence of sympatric species. It is necessary to better understand these factors and the interactions between them in the hominin fossil record to better understand taxonomic diversity and ecological strategies of early hominins.

Results and discussion

Let us briefly review human evolution, in order to understand this concept and to try to find answers to questions that are still confusing us today. Let us begin with the evolution of animals. Zoologists have classified the members of the animal kingdom according to their differences and similarities. We humans fall under this kingdom because we move and eat with our mouth we are vertebrates because of our backbone, and we are mammals because we are warm-blooded and we breast-feed our offspring. We are primates because we have grasping hands, flexible limbs, and a highly developed sense of vision. We are also members of the family Hominoidea, the taxonomic group which includes both humans and apes, because of the absence of a tail, swinging arms, and the shape of our teeth. The term hominoid refers to all present and past apes and humans, while hominid refers specifically to present and past humans (Price and Feinman 1993, 1997a, 1997b, c, d, e, f). Hominids are known as walking creatures with comparatively large brains humans today are the sole living representation of this group. According to some evolutionists, fossil bones and genetic studies indicate that the hominids shared an ancestor with the great African ape. It is at this point that the record becomes more complex, when the study of primate evolution turns into the study of hominid evolution. According to Richard Klein of Stanford University, determining the genus and species of the fossil bones of early humans is a very difficult task. The fragmentary pieces of the early fossil finds represent only a few hundred separate individuals. Determining the age of the fossils is also very difficult. He says paleo-anthropology is more like a court of law than a physics laboratory, where we reassess and even redraw the whole family tree on finding a new fragment (Price and Feinman 1993, 1997a, 1997b, c, d, e, f).

Although we humans differ considerably from apes, genetically we are closest to them of all hominoids. As far as our genetic composition is concerned we share 98.4% of our genetic material with chimpanzees, while gorillas are only 2.3% different from us genetically. These statistics show great similarities and suggests that the last ancestor shared by the great ape and human lines was probably a chimpanzee-like creature. Thus, changes in genetic regulatory mechanism play an important role in the evolution of different lineages.

Geography had quite an important influence in shaping the development of humanity. It was in the middle of the Tertiary period (5–25 million of years ago) when the climate was much warmer and wetter than what it is today, and tropical forests grew across much of Africa, Europe and Asia that an increase in the variety of mammals occurred. Many species of apes lived in these forests, including one that is considered by some to be the ancestor of modern humans.

Then sometime around 5 million years ago, towards the end of the Tertiary time, the global temperatures began to cool, ice caps formed at the poles, and the climate grew drier. As a result, the area of the tropical forests grew smaller, giving way to expanses of open woodland and grasslands. These developments did not occur all at once but evolved slowly. In East Africa the hominoids groups were trapped in shrinking patches of forest. Before this they had lived in the trees and moved on four feet when travelling around the forest bed. Now in order to cross wide stretches of open land quickly, some hominoids began walking on two feet, like modern humans. It was under these conditions that the hominids split from this ape or the hominoid group. It is believed that this whole process of hominization began in Africa, which is the only continent where fossils of early hominids dating back to four - 5 million years are found today. The distinction was made due to their new mode of locomotion, known as “bipedalism” (walking on two feet rather than on four). These early hominids are called australopithecines: specialist believe in addition to walking upright with two feet, they had comparatively larger brains and they depended on tools for their survival (Bahn 2002a, b, c, d, e).

While studying the fossils we also need to study how these beings modified objects and landscapes, thus creating an archaeological record. It is important to study both, as it helps us to understand how human beings evolved into what they are today. Some of the best evidence comes from sites at Hadar, Swartkrans, Olduvai, Laetoli and Koobi Fora. Some new fossil finds from Ethiopia, Kenya and Tanzania have pushed back the age of the earliest known hominids and have modified our understanding of their appearance and behavior (Price and Feinman 1993, 1997a, 1997b, c, d, e, f).

The oldest known Australopithecus species is A. Anamensis, which dates approximately 4 million years ago. The remaining early hominid fossils have been assigned to the species A. Afarensis, which includes the famous Lucy from Hadar (see Fig. 1 - A. Afarensis, Lucy from Hadar, Ethiopia), Ethiopia. Other direct evidence of hominid bipedalism is a fossilized trail of footprints some 3.6 million years old, found in eastern Africa at Laetoli, Tanzania (see Fig. 2 - Replica of the fossilized trail of footprints some 3.6 million years old, found in eastern Africa at Laetoli, Tanzania are exhibited in the National Museum of Nature and Science, Tokyo, Japan). Another evolutionary trend that occurred during this time was the change in dental pattern. Fossils of hominids dating back to three to 2 million years from southern and eastern African sites have small front teeth and large cheek teeth. Some form of gracile australopithecine is thought to have evolved into the first members of the genus homo about 2 million years ago, known as Homo habilis (which literally means handyman). Anthropologists continue to disagree about what caused this complete transition from ape to humans. Whereas many paleontologists believe that more than one species belonging to the genus homo may have co-existed in eastern Africa during the early Pleistocene, along with the robust australopithecines (species with massive teeth and jaws). It is also during this time that we find the oldest undisputed stone tools from Ethiopia, classified under the Oldowan tradition. By 1.8 million years ago the early homos had either disappeared or they evolved into H. erectus (upright man), the first member of the genus homo to spread out of Africa into Asia and Europe (see Fig. 3 - H. erectus (upright man), the first member of the genus homo to spread out of Africa into Asia and Europe.). They were taller than modern humans, but were very much like us in other respects, though their brains were still much smaller. It is assumed that they were capable of using fire and speech to a certain extent, and went, to far areas like Central Asia, Southwest Asia, South Asia, Europe and China. The Acheulean stone-tool tradition is associated with them. Archaeologists traditionally assign the Oldowan and Acheulean traditions to a single period known as the Lower Paleolithic in Europe and the Early Stone Age in Africa. But in recent years archaeologists have concluded that it is quite misleading to associate any Stone Age traditions uniquely to a single hominid species. Traditions can vary due to the availability of particular resources in different areas. Keeping all the above details in mind, paleoanthropologists consider a logical link between H. erectus, the more primitive hominids and our own species. They believe that the Acheulean stone – tool making ability was a determinant factor in the migration of early hominids out of Africa into new environments. The earliest handaxes found from outside of Africa are in Ubeidiya, Israel. While the punctuationists and gradualists continue to debate about the fate of H. erectus and the origin of the H. sapiens, up to this time indicates that our own species issued from H. erectus (Schultz and Lavenda 1998a, b, c, d).

Replica of the fossilized trail of footprints some 3.6 million years old, found in eastern Africa at Laetoli, Tanzania are exhibited in the National Museum of Nature and Science, Tokyo, Japan

H. erectus (upright man), the first member of the genus homo to spread out of Africa into Asia and Europe. (

Towards the end of the Tertiary Period the global climate had started to cool down and this continued into the next Quaternary Period, also known as the Ice Age (see Fig. 4 - Map of the Last Ice Age.). In spite of its name the climate was not cold all the time: there were frequent warm intervals interglacial periods, separate from the cold, dry glacial periods. As these changes were quite rapid, the animals and plants sometimes found it difficult and sometimes impossible to adapt and to survive under the new climatic changes. H. erectus responded to these changes by developing a bigger brain. This meant that greater intelligence was available now for problem solving. One million years ago the brain of H. erectus was approximately three - quarters the size of the modern human brain (Haywood 1997, 1989 n.d.,). But recent studies have shown that stone tools found in association with animal bones were not used for slaughtering animals but for cleaning the skins and cutting up the meat. Plants probably formed a large part of their diet. No ornaments or art work is found and neither is there any evidence of them burying their dead (Bahn 2002a, b, c, d, e). So the question remains, was H. erectus man’s ancestor?

It was sometime between 500,000 and 200,000 years ago that the fossils of H. erectus start to disappear from the fossil records and were replaced by fossils that show a mosaic of features found in H. erectus and H. sapiens (literally wise men). Though these fossils differ considerably from one another they collectively are known as archaic H. sapiens. They are poorly dated and paleoanthropologists find them difficult to classify and to relate specifically to H. sapiens. There are two major interpretations of the evidence of these fossil records. Punctuationists favor the “replacement model”: according to them H. erectus was a single, long- lived, geographically dispersed species, and had only one sub-population most probably located in Africa around 200,000 to 130,000 years ago that underwent evolutionary changes there to produce H. sapiens. Their descendants then later migrated to other regions. Whereas, the gradualists favor the “regional continuity model”. According to it H. erectus eventually evolved into H. sapiens gradually throughout the entire regions, retaining regionally distinct physical characteristics (Schultz and Lavenda 1998a, b, c, d). However, archaeologists have found no record to back the claim that either H. erectus or archaic H. sapiens was truly our ancestor. There is no evidence of personal ornamentation - jewelry, beads, or any kinds of art form, exists, nor are there paintings, sculptures or engravings that show that use of more than basic instincts. The ability to think and reason is still missing (Ingold 1994a, b, c). Therefore, whether they were really our ancestor, might be questioned.

In Europe a specie known as Neanderthals flourished between 130,000 and 35,000 years ago, they are considered by some to be the descendant of archaic H. sapiens. A large collection of fossils remains, tells us that they were shorter and more robust than modern H. sapiens with bulbous noses that helped them to survive cold conditions by reducing heat loss. But during the 1980s, new evidence revealed that Neanderthals appeared in Europe and western Asia at the same time anatomically modern H. sapiens appeared in Africa. These dates and the new evidence have made paleoanthropologists revise their traditional understanding of the relationship between Neanderthals and modern peoples. The archaic H. sapiens could no longer be considered the ancestors of the Neanderthals as data found in Israel suggests that the Neanderthals and the moderns lived side by side in south-western Asia for at least 45,000 years without losing their anatomical distinctiveness. Even more puzzling is the fact that both were using tools made in the same way. Mousterian experts disagree whether Neanderthals created a religion and whether hunting was important to them, but there is compelling fossil evidence from many sites and regions that they buried their dead and looked after their sick and old. Moreover, it seems probable, given the scant evidence for any form of art or ornamentation, that they did not make use of symbols, which is a critical element in the development of human language. Another thing that concerns us today is whether the Neanderthals and the moderns interbred, and whether the modern human populations today contain any Neanderthal genes. This situation creates a dispute among historians today (Schultz and Lavenda 1998a, b, c, d). There are many questions that come to mind. Why did the Neanderthals look after their sick and old? Why did they start to bury their dead? Why were they using tools? Some believe that all these actions can be related to basic instincts. Tool use is not a distinctive characteristic of humans but animals too may use or even make simple tools however, using tools to make other tools does distinguish humans from animals. For example, the sea otter wields a rock to break open the shell of an abalone. And the anthropologist Jane Goodall has observed chimpanzees using a variety of tools in their daily life: thrashing about with branches for display, using clubs and missiles for defense, selecting a twig and stripping its bark to probe the nests of termites and attract them to the stick, then to be eaten by the wise chimp. West African chimps even use stone and wooden hammers to crack and open nutshells (Price and Feinman 1993, 1997a, 1997b, c, d, e, f).

So, the question becomes was the Neanderthal man’s ancestor? Because when it came to something like creating symbols for speech they were unable to do so, since it required more brain capacity, reasoning and intelligence that they unfortunately lacked. The question whether the Neanderthals and modern humans interbred was recently addressed by paleoanthropologists who claim, that there was no interbreeding between the two. Mitochondrial DNA studies suggest that all humans living today are part of a relatively homogeneous population that originated in Africa within the last few hundred thousand years. In 1997, genetic researchers extracted and decoded a mitochondrial DNA fragment for the original Neander Valley specimen. The analysis revealed significant differences in its DNA from all living humans, suggesting that there was an ancient split between the two lineages, perhaps more than 500,000 years ago. Although, Neanderthals did not disappear from Western Europe until 30,000 years ago, possibly later, it is a common belief that modern H. sapiens may have forced them into extinction (Bahn 2002a, b, c, d, e).

Now let’s enter the last and the most important phase of human evolution. This phase is further divided into two phases. During the first phase, there is a general consensus among paleoanthropologists today that modern human (H. sapiens) evolved in Africa sometime between 100,000 to 150,000 years ago and spread around the globe. Recent studies in genetic evolution also support the view that Africa was the home of the original human population. However, debate continues about the nature of their dispersal. Most believe that a spreading wave of modern humans replaced existing populations of archaic H. sapiens entirely. This process of dispersal was complex and involved multiple movements of people and genes. In the caves of Qafzeh and Skhul in Israel remains of modern humans similar to found in Ethiopia and Tanzania, (150,000–100,000 years ago), and in South Africa (100,000–90,000 years ago) have been found. This is the first evidence that we have of modern humans (if they were) outside of Africa. Though, the fossils of these modern humans are still associated with the archaic stone tool traditions (like those of the Neanderthals), and like the ones also associated with the race of modern Africans (Bahn 2002a, b, c, d, e).

According to paleoanthropologists a second phase began roughly around 40,000 years ago, when “a behavioral revolution” took place: whether it was the continuity of the race or whether the race of the: “so called out of Africa H. sapiens” was totally replaced by the current human race are two questions that are under continuing discussion. But no one can disregard or refute the dramatic changes of many both in anatomy and in behavior, that have taken place over the last 40,000 years when compared with the previous million years. Recent evidence from molecular biology has added support to this picture of rapid and recent change, resulting in the current humans that are not only genetically but also behaviorally and anatomically modern. Evidence also points to an African center for the origin of modern humans. As they moved out of Africa they very soon replaced the variety of other Homo geneses roaming the world (Ingold 1994a, b, c).

Modern humans besides having many biological differences from other homo species are according to some “closer to the angles”. We possess many attributes that differentiate us from other species. Our large brain and intelligence enables us to think rationally and make decisions rather than to follow basic instincts like other species. We as humans have moved from purely instinctual behavior to reason and thought. We, in a given situation may flee from a fire, but we can also turn back into the same fire to save someone else (Price and Feinman 1993,1997a, 1997b, c, d, e, f). It is during this phase, that we see fully developed linguistic and modern technological skills which appear to have developed in the modern man. There is general disagreement as to when this really happened, as the evidence found in this regard is both uncertain and open to doubt. Some believe it was 100,000 years ago, whereas others say it was as recent as 50,000 to 40,000 years ago. However, according to the archaeological record, it is only after 50,000 years that we find abundant examples of art and advanced technology. The first uncontested ritual behavior evidence that we have are the ostrich eggshells beads found from Enkapune ya Muto (Kenya) dating to 46,000 years ago. Beside these archaeologists also witness the appearance of ornaments, engravings, sculptures, and other form of symbolism, which unmistakably confirm the presence of modern human language. But the fossils of this time remain ambiguous, because they lack any anatomical evidence for linguistic abilities. Despite lack of evidence found in the fossils, the archaeological record speaks louder than words. The manipulation of these symbols (ornaments, engravings, etc.) are linked with the fundamental improvements that occurred in technical abilities, which undoubtedly played an important role in the global spread of the modern human species. Their ability to invent new technologies and cope with different environments helped them to colonize the globe at a rapid speed (Bahn 2002a, b, c, d, e).

So, it would not be wrong to presume at this stage, that it was the abilities to talk, think, reason and communicate that differentiated modern humans from all other creatures before him. Clifford Geertz of Princeton University has described humans as,

“. toolmaking, talking, symbolizing animals: Only they laugh only they know when they will die only they disdain to mate with family members only they contrive those visions of other worlds called art. They have not just mentality but consciousness, not just needs but values, not just fears but conscience, not just a past but a history. Only they have culture.”

According to the famous anthropologist Leslie White, culture is our “extrasomatic” means of survival, it is the nonbiological, nongenetic behavior and sociability that have carried us through the millennia and spread us into diverse environments across the planet. So, in short, culture is a group of ideas and actions that are learned and transmitted from one generation to the next generation. Human culture embodies our experiences and behaviors which are summarized in our language and are transferred to us through our parents and peers. It is as impossible to have human identity without social contact as it is to have biological existence without parents. There is a famous story that Tarzan of the comic book and movie was an ape before he met Jane. It is only culture that enables us to find our place on earth, to create Gods, to anticipate death, to travel to the worlds beyond, and last but not the least to study archaeology, in order to find answers about our past (Price and Feinman 1993, 1997a, 1997b, c, d, e, f). It was this cultural development, which was both very rapid and at an alarming speed, that until today evolutionists, biological scientist, paleoanthropologist and many more have been unable to understand. For example, if we can believe the evolutionist man’s ancestor first appeared on earth 4 million years ago and then slowly evolved into Modern Human only around 40,000 years ago. While keeping this in mind we witness, that after 40,000 to 10,000 years age man not only developed new technologies, but he also modified his environment. And only 10,000 years have taken him from bows and arrows to thermonuclear weapons, and the production of the latter has taken only twenty more years (The New Encyclopedia Britannica n.d.).

Another important fact that seems to refute the claim of the evolutionists today is that, there are no signs of any intermediate forms found in the fossil records. Charles Darwin, who is known as the father of the theory of evolution, as state in his book, The Origins of Species claims,

“If my theory be true, numberless intermediate varieties, linking most closely all of the species of the same group together must assuredly have existed. Consequently, evidence of their former existence could be found only amongst fossil remains.”(Darwin 1964)

The fossil records today show few intermediate forms on the other hand, we see fully-formed living species seem to emerge suddenly without any evolutionary transitional form between them. This lack of factual evidence is enough to back their claim that all living species are created separately, and that life appeared on earth all of a sudden and fully-formed. Derek V. Ager, a famous British evolutionist admits this fact by saying

“The point emerges that if we examine the fossil record in detail, whether at the level of Orders or of Species, we find – over and over again – not gradual evolution, but the sudden explosion of one group at the expense of another.”(Ager 1976)

The fact that all living species were created separately, suddenly and fully-formed without any evolutionary ancestor is yet again backed by evolutionist biologist Douglas Futuyma, who claimed,

“Creation and evolution, between them, exhaust the possible explanations for the origin of living things. Organisms either appeared on the earth fully developed or they did not. If they did not, they must have developed from pre-existing species by some process of modification. If they did appear in a fully developed state, they must indeed have been created by some omnipotent intelligence.”(Futuyma 1983)

Fossil records today back this claim that all living species emerged fully developed and in a perfect state on earth.

The fossil record of humans is notoriously patchy and incomplete. Even so, skeletal remains and artifacts unearthed in Africa in recent decades have done much to illuminate human evolution. But what is the origin of the genus Homo? Villmoare et al. found a fossil mandible and teeth from the Afar region in Ethiopia. The find extends the record of recognizable Homo by at least half a million years, to almost 2.8 million years ago. The morphological traits of the fossil align more closely with Homo than with any other hominid genus. DiMaggio et al. confirm the ancient date of the site and suggest that these early humans lived in a setting that was more open and arid than previously thought.

Sedimentary basins in eastern Africa preserve a record of continental rifting and contain important fossil assemblages for interpreting hominin evolution. However, the record of hominin evolution between 3 and 2.5 million years ago (Ma) is poorly documented in surface outcrops, particularly in Afar, Ethiopia. Here we present the discovery of a 2.84– to 2.58–million-year-old fossil and hominin-bearing sediments in the Ledi-Geraru research area of Afar, Ethiopia, that have produced the earliest record of the genus Homo. Vertebrate fossils record a faunal turnover indicative of more open and probably arid habitats than those reconstructed earlier in this region, which is in broad agreement with hypotheses addressing the role of environmental forcing in hominin evolution at this time. Geological analyses constrain depositional and structural models of Afar and date the LD 350-1 Homo mandible to 2.80 to 2.75 Ma.

Surface exposures of fossiliferous sedimentary rocks dated between 3.0 and 2.5 million years ago (Ma) are rare throughout Africa, yet are of great interest because this interval overlaps with shifts in African climate (15), corresponds to faunal turnover (68), and represents an important gap in our knowledge of evolutionary events in the human lineage (9). The time period coincides with changing geologic conditions in eastern Africa, as rifting processes (10, 11) and extensive volcanism (12) altered the architecture of sedimentary basins (1315), controlling the paleogeography of hominin and other mammalian habitats. In tectonically active areas such as the lower Awash Valley (LAV), Afar, Ethiopia, rift-basin dynamics create spatially variable and often incomplete records of deposition. At other fossil sites in the LAV, the fluvio-lacustrine sediments of the Hadar Formation (

3.8 to 2.9 Ma) are separated from the younger fluvial sediments of the Busidima Formation (

2.7 to 0.16 Ma) by an erosional unconformity (14, 16). The Hadar region contains early Homo dated to

2.35 Ma (9) and an excellent record of Australopithecus afarensis from 3.5 to 2.95 Ma (17). However, the absence of fossiliferous sediments in the Hadar region due to the unconformity has impeded efforts to document a continuous record of hominin and other faunal evolution, and limits our understanding of regional habitat change in the LAV. Recent field investigations and geochronological analysis of sedimentary deposits at Ledi-Geraru (LG), located northeast of Hadar, Gona, and Dikika (Fig. 1), confirm the presence of late Pliocene fossiliferous sedimentary rocks dated to the interval represented elsewhere in the region by the erosional unconformity (18). Here we present the geology, chronostratigraphy, and paleontology of the Lee Adoyta region of LG, where the LD 350-1 early Homo mandible (19) and 614 other mammal specimens were recovered from sediments dated 2.84 to 2.58 Ma (Fig. 1).

(A) The LAV (yellow square), Afar Depression (gray area), Ethiopia. RS, Red Sea GOA, Gulf of Aden MER, Main Ethiopian Rift. (B) LAV project areas and the approximate mapped extent of the Hadar Formation senso stricto. The Busidima Formation is largely exposed in the areas of Hadar, Gona, and Dikika. (C) Sediments and volcanic rocks in the eastern LG research project area are cut by two sets of faults striking NW and NNE, indicating the influence of both the RS and MER extensional systems, respectively. At Lee Adoyta, NW-trending faults are most significant and appear to cross-cut NNE faults. Regions referred to in the text are labeled in black.

The Lee Adoyta region preserves an

70–m-thick sedimentary sequence that is cut by multiple closely spaced NW-SE (320° to 340°)–trending faults that postdate deposition (Figs. 1 and 2). Geologic mapping documents drag folds and stratigraphic juxtaposition to define the normal sense of motion along the faults, which is consistent with faulting patterns oriented NW-SE associated with Red Sea rift extension (14). There are four major fault-bounded blocks, each of which comprises a discrete sedimentary package (Fig. 2).

(A) Geologic map of the region surrounding the Lee Adoyta hominin site (yellow star) showing NW-SE–oriented faults dissecting sedimentary packages into discrete blocks. We mapped the 900 × 500–m area in the field using high-resolution (1 m) stereo imagery and Global Positioning System technology. (B) West-to-east cross section of Lee Adoyta. The older Bulinan and Gurumaha fault blocks are uplifted relative to the younger adjacent Lee Adoyta and Garsalu fault blocks.

The Bulinan sedimentary package is 10 m thick and consists of lacustrine deposits (laminated silty claystone with dispersed gastropod shells) with five intercalated 2- to 12-cm-thick altered tuffs (Fig. 3). The crystal-rich Bulinan Tuff lies 4 m above the base of the section. It is 2 to 3 cm thick, light pink in color, and composed of altered volcanic glass with <15% subangular lithic fragments and feldspar grains. The Bulinan Tuff was dated by the laser single-crystal incremental heating (SCIH) 40 Ar/ 39 Ar technique on individual grains of phenocrystic Na-plagioclase feldspar from a single sample. Age “plateaus” as revealed in 39 Ar release spectra indicate the characteristic age of the feldspars. The population of those ages yielded a weighted-mean result of 2.842 ± 0.010 Ma (1σ internal error ± 0.014 Ma external error n = 4 grains) (figs. S2 to S4 and table S2). Just four fossils have been recovered from this fault block, and therefore an inference of habitat based on fauna is precluded.

The dip and sense of motion along each fault bounding the sediment packages are shown to separate the packages and thus establish relative ages. Section locations (numbered) are provided in Fig. 2.

The Gurumaha sedimentary package, which yielded the LD 350-1 hominin, is

21 m thick and dips 3° to 5° E-SE. Gurumaha sediments coarsen up-section and include laminated mudstone with thin, fine sandstones, siltstone, and coarse cross-bedded sandstone with pebble lags. The package is capped by a fluvial sequence composed of a carbonate nodule–rich, cross-bedded pebble conglomerate and overlying sands with minimal basal scour. The Gurumaha Tuff is a crystal-rich lapilli tephra-fall deposit that contains pumice (table S5) and forms a continuous white to light gray stratigraphic marker 8 to 10 cm thick (Fig. 2). The Gurumaha Tuff was dated by the SCIH technique applied to four samples containing anorthoclase to Na-plagioclase feldspar phenocrysts. A weighted mean of the plateau ages yielded 2.822 ± 0.006 Ma (± 0.015 Ma external error n = 23 grains) (figs. S2 to S4 and table S2). This age falls within chron C2An.1n (Gauss) of the astronomical polarity time scale (20), consistent with the normal paleomagnetic polarity measured for the entire Gurumaha sequence (Fig. 3). The age on the tuff provides a maximum age for the LD 350-1 hominin fossil, which was recovered from a vertebrate fossil–rich silt horizon 10 m conformably above the Gurumaha Tuff and 1 m below the base of the capping pebble conglomerate (19). Based on local and regional sedimentation rates, a refined age estimate of 2.80 to 2.75 million years is calculated for the fossiliferous horizon (19).

Ecological community structure analysis based on mammalian fauna recovered from the Gurumaha fault block indicates a more open habitat (mostly mixed grasslands/shrublands with gallery forest) that probably experienced less rainfall than any of those reconstructed for the members of the Hadar Formation (6). The landscape was similar to modern African open habitats, such as the Serengeti Plains, Kalahari, and other African open grasslands, given the abundance of grazing species and lack of arboreal taxa, although the presence of Deinotherium bozasi and tragelphins probably indicates a gallery forest (fig. S6). The existence of Kobus sigmoidalis, aff. Hippopotamus afarensis, crocodiles, and fish in this package reflects the presence of rivers and/or lakes. Approximately one-third of the mammalian taxa present are shared with those in the youngest Hadar Formation (

3 Ma), whereas one-third are first appearances of these taxa in the LAV (Table 1). The remaining one-third of mammals recovered can only be identified to the genus level.

Key: X, present 0, absent *, taxa shared with the Kada Hadar submember 2 + , species previously unrecorded in the LAV, including chronospecies.

The Lee Adoyta sedimentary package is

22 m thick and approximately horizontal. Two tuffs separated stratigraphically by

8 to 10 cm approximate the base of the Lee Adoyta package. The lower tuff is a 5- to 6-cm-thick basaltic ash typically altered to a yellowish bentonite. The upper unit is a 4- to 5-cm-thick light gray vitric-crystal tuff (table S6). The Lee Adoyta Tuffs are encased in brown fissile mudstone that directly overlies a green Vertisol. The overlying sedimentary units include brown mudstone, basalt-rich sandstone, and a pebble conglomerate. A 1.5-m-thick, cross-laminated, unnamed glassy tuff caps the section (table S6). Na-plagioclase phenocrysts from the upper Lee Adoyta Tuff have a weighted-mean SCIH age of 2.669 ± 0.011 Ma (± 0.03 Ma external n = 5 grains) (figs. S2 to S4 and table S2). Paleomagnetic measurements record a transition from normal to reverse polarity

12 m above the Lee Adoyta Tuffs (Fig. 3), which is probably the Gauss/Matuyama reversal at 2.581 Ma (20). The date and stratigraphic position of the Lee Adoyta Tuffs are consistent with its assignment to the C2An1.n chron (Gauss), and provide a minimum age constraint for the LD 350-1 fossil. The Lee Adoyta fault block yielded mammalian fauna with

80% taxonomic overlap with the Gurumaha fauna, and the ecological community structure also reconstructs an open habitat (fig. S6 and Table 1).

The Garsalu sedimentary package encompasses strata exposed along the margins of the Lee Adoyta drainage (Fig. 2). We correlate these packages based on the similarity of sedimentary facies and downfaulting against adjacent fault blocks. These fluvial deposits are

26 m thick, gently dipping, and include paleosols, sandstones, siltstones, and conglomerates (Fig. 3). The Garsalu sedimentary package is the youngest (<2.58 Ma) in the Lee Adoyta region, based on faulting relationships and the presence of Connochaetes gentryi.

The combined 70-m-thick section at Lee Adoyta is placed within the chronostratigraphic framework of the LAV in an interval previously undocumented in the regional sedimentary record (fig. S8). In general, the sedimentary deposits at Lee Adoyta coarsen upward and represent a variety of depositional environments. At Lee Adoyta, a paleolake (

2.84 Ma) extended at least 6 km north to Ambare and Mafala (Fig. 1C), where lacustrine deposits are present in similarly aged strata (18). The depositional environment progressed to a nearshore delta plain by 2.82 Ma, as indicated by sandy channel bodies and the presence of crocodiles, fish, and mammals in the Gurumaha sediments. At present, sedimentary deposits between the top of the Gurumaha sedimentary package (2.80 to 2.75 Ma) and the Lee Adoyta Tuffs (2.67 Ma) have not been observed. The Lee Adoyta fault block strata (<2.67 Ma) are coeval with a portion of the Busidima Formation and similarly capture a fluvial record probably deposited by tributaries to the ancestral Awash River system (16).

Geological investigations at Lee Adoyta allow us to place constraints on regional basin models. The presence of deposits dated to 2.8 Ma in eastern LG is consistent with continued deposition in the Hadar Basin as a result of northeastern migration of paleo Lake Hadar during the late Pliocene to early Pleistocene (14, 2123). Sometime between 2.95 and 2.7 Ma, changes in base level associated with Main Ethiopian Rift extension eroded Hadar Basin sedimentary deposits in the areas of Gona, Hadar, Dikika, and central and southern LG, creating an erosional unconformity (Fig. 1B and fig. S8) (14, 15, 18, 24). The preservation of 2.8-Ma sediments in eastern LG, but not elsewhere in the lower Awash, suggests that the unconformity did not extend as far east as Lee Adoyta (or at least was not as long in duration). This may be related to the proximity of Lee Adoyta to border faults, spatial variability of base level changes, or localized downfaulting of eastern LG before erosion. Lee Adoyta lies beyond the proposed eastern margin of the Busidima half-graben (14, 15). Therefore, the <2.7-Ma deposits at Lee Adoyta were either deposited in a different basin, or the Busidima half-graben was larger and more variable than proposed. After

2.6 Ma, NW-SE trending faults that cross-cut all sedimentary packages (Fig. 1C) indicate that Red Sea rifting was the dominant extensional regime.

2.8 Ma and resultant increases in African climatic variability and aridity are hypothesized to have spurred cladogenetic events in various mammalian lineages, including hominins (1, 2, 7). The faunal changes evident at Lee Adoyta appear to be in accord with these hypotheses, because the 2.8-Ma record shows a mammalian species turnover that includes first appearance datums and the dispersal of immigrant taxa previously unknown in Afar. Additionally, mammal communities in the Gurumaha and Lee Adoyta sedimentary packages indicate open habitats, with most vegetation cover consisting of grasses or low shrubs, a pattern that contrasts with the older, Australopithecus afarensis–bearing, Hadar Formation. Although the Lee Adoyta data provide enticing evidence for a correlation between open habitats linked to African aridification and the origins of the genus Homo, evidence from other sites in eastern Africa shortly after 3 Ma does not show a uniform transition toward open habitats (8, 2527). Ongoing research efforts in the eastern LG continue to explore previously undocumented sedimentary exposures that may allow us to test the hypothesis that the Lee Adoyta record samples a drier habitat of a larger, more variable ecosystem or represents a distinct arid phase in Afar during the late Pliocene.

Paige Fossil History

“The middle Pliocene gets crowded.” New fossils have recently been announced that were found in East Africa by a team of scientists led by Yohannes Haile-Selassie of the Cleveland Museum of Natural History. According to Haile-Selassie, these fossil fragments constitute a new species of hominin! The creature has been named Australopithecus deyiremeda, combining the word deyi, meaning close, with remeda, meaning relative in the local Afar language. Haile-Selassie et al. argue that Au. deyiremeda is similar in many ways –but also different from0–contemporary species such as Australopithecus afarensis (Lucy!).

I haven’t stopped talking about the fossil since it was announced, so I thought I’d write about it! Disclaimer: this is science in the process, nothing is definitive and not all paleoanthropologists agreed with Haile-Selassie’s conclusions. I’m simply imagining what this could mean if this does, in fact, turn out to be a new species of Australopiths. I try to use language such as”potentially” to reinforce that.

Let’s recap: the team found a couple of lower jaws, as well as that beautiful upper jaw you see in the photo above, and some teeth. So what can paleoanthropologists determine based on some fragmentary bits of jaws and teeth? Well, it turns out, a lot! Teeth have changed dramatically over the course of human evolution, so minute differences tell us a lot about how these creatures were similar and dissimilar from other hominin species. It potentially tells us a bit about what they might have been eating, their behavior, and more. Also, the shape and features of the jaws provide more clues about what they were eating–was it hard to chew? did they need certain types of force? etc–because the shape and features tell us where chewing muscles were located.

  • This could mean that multiple species co-existed in the Middle Pliocene. In a Nature article, Fred Spoor even called the middle Pliocene “crowded,” which I find amusing and interesting. Prior to this discovery, some paleoanthropologists had already been stating that there is evidence for taxonomic diversity at this point in time, but the fossil record was fragmentary and the primary example Kenyananthropus platyops was very distorted & hard to read. Therefore, Au. deyiremeda adds to the mounting evidence for species co-existing around 3.5 million years ago, which is pretty cool.
  • BUT WAIT: Not only did multiple species potentially co-exist, two species were neighbors. This really gets to the heart of how crazy this discovery is: Au. deyiremeda was found approximately 22 miles from the Hadar site that has revealed so many Au. afarensis fossils. I encourage you to really let this sink in. 22 miles. In the vast, East African desert. If this really is a separate species from Au. afarensis then the interesting question is how did they co-exist in such close proximity? Did they happen to be interested in different resources, so the competition was less intense?

If I had to chose one bottom line that I think this find possibly illustrates: Hominin species diversity might permeate human evolution at every stage in the game. It seems as though we are starting to see possible taxonomic diversity at every stage of human evolution (until the present, of course). We potentially see this recently with Homo floresiensis, Neandertals, and Denisovans, we see it in the Middle Pleistocene (200,000-800,000 years ago), and so on.

Now, what’s questionable about this?

    Are fragmentary pieces of jaws enough? Some paleoanthropologists are skeptical that a new species can be named based on these fragmentary bits. Those who aren’t big fans of species diversity, such as Tim White, are inclined to put these fossils in with Au. afarensis. The NY Times quoted him as having said “Lucy’s species just got a few more new fossils” in response to the fossil announcement. Paleoanthropologist Bill Kimbel was also cautious about the discovery, stating that “the distinctions [between these fossils and others such as Au. afarensis] are very, very subtle,” Kimbel continued, “I think it’s a judgment call as to whether you think the differences amount to a species-level difference.”

Many of these claims are still preliminary, but this could paint a cool picture of human evolution about 3.5 million years ago. Taxonomic diversity raises questions like: if all these species were running around, which one gave rise to us? The tree of life seems to be getting fuller (though some disagree- calling it more of a Saguaro cactus), which makes evolutionary relationships harder to trace and–I think–makes the whole game more fun.