Hominin dental remains from the Pliocene localities at Lomekwi, Kenya (1982-2009).

Increasing evidence for both taxonomic diversity and early stone manufacture during the Pliocene highlights the importance of the hominin fossil record from this epoch in eastern Africa. Here, we describe dental remains from Lomekwi (West Turkana, Kenya), which date from between 3.2 and 3.5 Ma. The sample was collected between 1982 and 2009 and includes five gnathic specimens and a total of 67 teeth (mostly isolated permanent postcanine teeth). Standard linear dimensions indicate that, although the Lomekwi teeth are relatively small, there is broad overlap in size with contemporary Australopithecus afarensis and Australopithecus deyiremeda specimens at most tooth positions. However, some dental characters differentiate this sample from these species, including a relatively large P4 and M3 compared with the M1, a high incidence of well-developed protostylids, and specific accessory molar cuspules. Owing to a lack of well-preserved tooth crowns (and the complete absence of mandibular teeth) in the holotype and paratype of Kenyanthropus platyops, and limited comparable gnathic morphology in the new specimens, it cannot be determined whether these Lomekwi specimens should be attributed to this species. Attribution of these specimens is further complicated by a lack of certainty about position along the tooth row of many of the molar specimens. More comprehensive shape analyses of the external and internal morphology of these specimens, and additional fossil finds, would facilitate the taxonomic attribution of specimens in this taxonomically diverse period of human evolution.

Complete permanent mandibular dentition of early Homo from the upper Burgi Member of the Koobi Fora Formation, Ileret, Kenya.

The KNM-ER 64060 dentition derives from a horizon that most likely dates to between 2.02 and 2.03 Ma. A proximate series of postcranial bones (designated KNM-ER 64061) derives from the same siltstone unit and may be associated with the dentition, but their separation on the surface of the site leaves some room for doubt. KNM-ER 64060 is one of fewer than ten hominin specimens from the Early Pleistocene of East Africa that comprises a full or nearly complete mandibular dentition. Its taxonomic attribution is potentially significant, especially if the postcranial elements are related. At least three, and probably four hominin species, including Paranthropus boisei and Homo erectus (= H. ergaster), are known at about this time in East Africa. Other penecontemporaneous fossils have been referred to a single, highly variable species, H. habilis, or two taxa, namely H. habilis and H. rudolfensis. Although the weight of evidence supports the attribution of these specimens to two species, there is notable lack of agreement over the assignation of individual fossils. We take a conservative approach and group all such specimens under the designation "early Homo sp." for comparative purposes. KNM-ER 64060 is clearly attributable to Homo rather than Paranthropus. The preponderance of the evidence suggests that the affinities of KNM-ER 64060 are with fossils assigned to the early Homo sp. category rather than with H. erectus. This is indicated by the overall sizes of the KNM-ER 64060 canine, premolar and molar crowns, the size relationships of the P3 to P4, the relative narrowness of its premolar crowns, the cusp proportions of the M1 and especially those of the M2 and M3, and seemingly the possession of a two-rooted P4. Some of these comparisons suggest further that among the fossils comprising the early Homo sp. sample, the KNM-ER 64060 dentition exhibits greater overall similarity to specimens such as OH 7 and OH 16 that represent Homo habilis sensu stricto.

Evolution and function of the hominin forefoot.

The primate foot functions as a grasping organ. As such, its bones, soft tissues, and joints evolved to maximize power and stability in a variety of grasping configurations. Humans are the obvious exception to this primate pattern, with feet that evolved to support the unique biomechanical demands of bipedal locomotion. Of key functional importance to bipedalism is the morphology of the joints at the forefoot, known as the metatarsophalangeal joints (MTPJs), but a comprehensive analysis of hominin MTPJ morphology is currently lacking. Here we present the results of a multivariate shape and Bayesian phylogenetic comparative analyses of metatarsals (MTs) from a broad selection of anthropoid primates (including fossil apes and stem catarrhines) and most of the early hominin pedal fossil record, including the oldest hominin for which good pedal remains exist, Ardipithecus ramidus Results corroborate the importance of specific bony morphologies such as dorsal MT head expansion and "doming" to the evolution of terrestrial bipedalism in hominins. Further, our evolutionary models reveal that the MT1 of Ar. ramidus shifts away from the reconstructed optimum of our last common ancestor with apes, but not necessarily in the direction of modern humans. However, the lateral rays of Ar. ramidus are transformed in a more human-like direction, suggesting that they were the digits first recruited by hominins into the primary role of terrestrial propulsion. This pattern of evolutionary change is seen consistently throughout the evolution of the foot, highlighting the mosaic nature of pedal evolution and the emergence of a derived, modern hallux relatively late in human evolution.

Reconstruction, endocranial form and taxonomic affinity of the early Homo calvaria KNM-ER 42700.

When first described, the small calvaria KNM-ER 42700 from Ileret, Kenya, was considered a late juvenile or young adult and assigned to Homo erectus. However, this species attribution has subsequently been challenged because the specimen's neurocranial shape differs substantially from that of H. erectus adults. Here, (1) we describe the postmortem damage and deformation that could have influenced previous shape analyses, (2) present digital reconstructions based on computed tomographic scans correcting for these taphonomic defects, and (3) analyze the reconstructed endocranial shape and form, considering both static allometry among adults and ontogenetic allometry. To this end, we use geometric morphometrics to analyze the shape of digital endocasts based on landmarks and semilandmarks. Corroborating previous studies of the external surface, we find that the endocranial shape of KNM-ER 42700 falls outside the known adult variation of H. erectus. With an endocranial volume estimate between 721 and 744 ml, size cannot explain its atypical endocranial shape when static allometry within H. erectus is considered. However, the analysis of ontogenetic allometry suggests that it may be a H. erectus individual that is younger than previously thought and had not yet reached adult endocranial shape. Future work should therefore comprehensively review all cranial indicators of its developmental age, including closure of the spheno-occipital synchondrosis. An alternative hypothesis is that KNM-ER 42700 represents an as yet unidentified species of early Homo. Importantly, KNM-ER 42700 should not be included in the adult hypodigm of H. erectus.

An ecometric analysis of the fossil mammal record of the Turkana Basin.

Although ecometric methods have been used to analyse fossil mammal faunas and environments of Eurasia and North America, such methods have not yet been applied to the rich fossil mammal record of eastern Africa. Here we report results from analysis of a combined dataset spanning east and west Turkana from Kenya between 7 and 1 million years ago (Ma). We provide temporally and spatially resolved estimates of temperature and precipitation and discuss their relationship to patterns of faunal change, and propose a new hypothesis to explain the lack of a temperature trend. We suggest that the regionally arid Turkana Basin may between 4 and 2 Ma have acted as a 'species factory', generating ecological adaptations in advance of the global trend. We show a persistent difference between the eastern and western sides of the Turkana Basin and suggest that the wetlands of the shallow eastern side could have provided additional humidity to the terrestrial ecosystems. Pending further research, a transient episode of faunal change centred at the time of the KBS Member (1.87-1.53 Ma), may be equally plausibly attributed to climate change or to a top-down ecological cascade initiated by the entry of technologically sophisticated humans.This article is part of the themed issue 'Major transitions in human evolution'.

Dietary changes of large herbivores in the Turkana Basin, Kenya from 4 to 1 Ma.

A large stable isotope dataset from East and Central Africa from ca. 30 regional collection sites that range from forest to grassland shows that most extant East and Central African large herbivore taxa have diets dominated by C4 grazing or C3 browsing. Comparison with the fossil record shows that faunal assemblages from ca. 4.1-2.35 Ma in the Turkana Basin had a greater diversity of C3-C4 mixed feeding taxa than is presently found in modern East and Central African environments. In contrast, the period from 2.35 to 1.0 Ma had more C4-grazing taxa, especially nonruminant C4-grazing taxa, than are found in modern environments in East and Central Africa. Many nonbovid C4 grazers became extinct in Africa, notably the suid Notochoerus, the hipparion equid Eurygnathohippus, the giraffid Sivatherium, and the elephantid Elephas. Other important nonruminant C4-grazing taxa switched to browsing, including suids in the lineage Kolpochoerus-Hylochoerus and the elephant Loxodonta. Many modern herbivore taxa in Africa have diets that differ significantly from their fossil relatives. Elephants and tragelaphin bovids are two groups often used for paleoecological insight, yet their fossil diets were very different from their modern closest relatives; therefore, their taxonomic presence in a fossil assemblage does not indicate they had a similar ecological function in the past as they do at present. Overall, we find ecological assemblages of C3-browsing, C3-C4-mixed feeding, and C4-grazing taxa in the Turkana Basin fossil record that are different from any modern ecosystem in East or Central Africa.

3.3-million-year-old stone tools from Lomekwi 3, West Turkana, Kenya.

Human evolutionary scholars have long supposed that the earliest stone tools were made by the genus Homo and that this technological development was directly linked to climate change and the spread of savannah grasslands. New fieldwork in West Turkana, Kenya, has identified evidence of much earlier hominin technological behaviour. We report the discovery of Lomekwi 3, a 3.3-million-year-old archaeological site where in situ stone artefacts occur in spatiotemporal association with Pliocene hominin fossils in a wooded palaeoenvironment. The Lomekwi 3 knappers, with a developing understanding of stone's fracture properties, combined core reduction with battering activities. Given the implications of the Lomekwi 3 assemblage for models aiming to converge environmental change, hominin evolution and technological origins, we propose for it the name 'Lomekwian', which predates the Oldowan by 700,000 years and marks a new beginning to the known archaeological record.

Associated ilium and femur from Koobi Fora, Kenya, and postcranial diversity in early Homo.

During the evolution of hominins, it is generally accepted that there was a shift in postcranial morphology between Australopithecus and the genus Homo. Given the scarcity of associated remains of early Homo, however, relatively little is known about early Homo postcranial morphology. There are hints of postcranial diversity among species, but our knowledge of the nature and extent of potential differences is limited. Here we present a new associated partial ilium and femur from Koobi Fora, Kenya, dating to 1.9 Ma (millions of years ago) that is clearly attributable to the genus Homo but documents a pattern of morphology not seen in eastern African early Homo erectus. The ilium and proximal femur share distinctive anatomy found only in Homo. However, the geometry of the femoral midshaft and contour of the pelvic inlet do not resemble that of any specimens attributed to H. erectus from eastern Africa. This new fossil confirms the presence of at least two postcranial morphotypes within early Homo, and documents diversity in postcranial morphology among early Homo species that may reflect underlying body form and/or adaptive differences.

Stable isotope-based diet reconstructions of Turkana Basin hominins.

Hominin fossil evidence in the Turkana Basin in Kenya from ca. 4.1 to 1.4 Ma samples two archaic early hominin genera and records some of the early evolutionary history of Paranthropus and Homo. Stable carbon isotopes in fossil tooth enamel are used to estimate the fraction of diet derived from C3 or C4 resources in these hominin taxa. The earliest hominin species in the Turkana Basin, Australopithecus anamensis, derived nearly all of its diet from C3 resources. Subsequently, by ca. 3.3 Ma, the later Kenyanthropus platyops had a very wide dietary range--from virtually a purely C3 resource-based diet to one dominated by C4 resources. By ca. 2 Ma, hominins in the Turkana Basin had split into two distinct groups: specimens attributable to the genus Homo provide evidence for a diet with a ca. 65/35 ratio of C3- to C4-based resources, whereas P. boisei had a higher fraction of C4-based diet (ca. 25/75 ratio). Homo sp. increased the fraction of C4-based resources in the diet through ca. 1.5 Ma, whereas P. boisei maintained its high dependency on C4-derived resources.

New fossils from Koobi Fora in northern Kenya confirm taxonomic diversity in early Homo.

Since its discovery in 1972 (ref. 1), the cranium KNM-ER 1470 has been at the centre of the debate over the number of species of early Homo present in the early Pleistocene epoch of eastern Africa. KNM-ER 1470 stands out among other specimens attributed to early Homo because of its larger size, and its flat and subnasally orthognathic face with anteriorly placed maxillary zygomatic roots. This singular morphology and the incomplete preservation of the fossil have led to different views as to whether KNM-ER 1470 can be accommodated within a single species of early Homo that is highly variable because of sexual, geographical and temporal factors, or whether it provides evidence of species diversity marked by differences in cranial size and facial or masticatory adaptation. Here we report on three newly discovered fossils, aged between 1.78 and 1.95 million years (Myr) old, that clarify the anatomy and taxonomic status of KNM-ER 1470. KNM-ER 62000, a well-preserved face of a late juvenile hominin, closely resembles KNM-ER 1470 but is notably smaller. It preserves previously unknown morphology, including moderately sized, mesiodistally long postcanine teeth. The nearly complete mandible KNM-ER 60000 and mandibular fragment KNM-ER 62003 have a dental arcade that is short anteroposteriorly and flat across the front, with small incisors; these features are consistent with the arcade morphology of KNM-ER 1470 and KNM-ER 62000. The new fossils confirm the presence of two contemporary species of early Homo, in addition to Homo erectus, in the early Pleistocene of eastern Africa.

Hominin diversity in the Middle Pliocene of eastern Africa: the maxilla of KNM-WT 40000.

The 3.5-Myr-old hominin cranium KNM-WT 40000 from Lomekwi, west of Lake Turkana, has been assigned to a new hominin genus and species, Kenyanthropus platyops, on the basis of a unique combination of derived facial and primitive neurocranial features. Central to the diagnosis of K. platyops is the morphology of the maxilla, characterized by a flat and relatively orthognathic subnasal region, anteriorly placed zygomatic processes and small molars. To study this morphology in more detail, we compare the maxillae of African Plio-Pleistocene hominin fossils and samples of modern humans, chimpanzees and gorillas, using conventional and geometric morphometric methods. Computed tomography scans and detailed preparation of the KNM-WT 40000 maxilla enable comprehensive assessment of post-mortem changes, so that landmark data characterizing the morphology can be corrected for distortion. Based on a substantially larger comparative sample than previously available, the results of statistical analyses show that KNM-WT 40000 is indeed significantly different from and falls outside the known range of variation of species of Australopithecus and Paranthropus, contemporary Australopithecus afarensis in particular. These results support the attribution of KNM-WT 40000 to a separate species and the notion that hominin taxonomic diversity in Africa extends back well into the Middle Pliocene.