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Suids are among the most common mammalian groups in the Plio-Pleistocene vertebrate fossil record of Africa and the most studied largely due to their significance as biochronological indicators. However, despite their abundance in the fossil record, the remains are mostly isolated teeth and fragmentary crania and mandibles. As a result, disagreements have persisted in terms of their taxonomy and phylogenetic relationships. Here, we present for the first time a detailed description of the cranial anatomy of Nyanzachoerus jaegeri based on two crania recovered from middle Pliocene deposits of the Woranso-Mille paleontological study area, Afar region, Ethiopia. Understanding the cranial morphology of this species is particularly significant given the recent reclassification of Nyanzachoerus jaegeri to the genus Notochoerus based largely on the incisor and symphyseal morphology of specimens from Kanapoi, Kenya. Here, we show that the two genera are clearly distinguished from each other by distinct morphological features of the cranium such as the shape of the braincase, orientation of the zygomatic arches, and premolar/molar ratio, among others. Furthermore, we show that the mandibular and dental morphological features identified by some workers as characteristic of Notochoerus are variable among tetraconodont species and that Nyanzachoerus jaegeri best fits within the genus Nyanzachoerus.

Middle Pliocene hominin species diversity has been a subject of debate over the past two decades, particularly after the naming of Australopithecus bahrelghazali and Kenyanthropus platyops in addition to the well-known species Australopithecus afarensis. Further analyses continue to support the proposal that several hominin species co-existed during this time period. Here we recognize a new hominin species (Australopithecus deyiremeda sp. nov.) from 3.3-3.5-million-year-old deposits in the Woranso-Mille study area, central Afar, Ethiopia. The new species from Woranso-Mille shows that there were at least two contemporaneous hominin species living in the Afar region of Ethiopia between 3.3 and 3.5 million years ago, and further confirms early hominin taxonomic diversity in eastern Africa during the Middle Pliocene epoch. The morphology of Au. deyiremeda also reinforces concerns related to dentognathic (that is, jaws and teeth) homoplasy in Plio-Pleistocene hominins, and shows that some dentognathic features traditionally associated with Paranthropus and Homo appeared in the fossil record earlier than previously thought.

The Woranso-Mille paleontological study area, located in the central Afar region of Ethiopia, is one of the most important Pliocene sites in eastern Africa. Since the Woranso-Mille Research Project began its investigation in 2005, more than 7,500 mammalian fossils, including hominins, have been collected from 80 vertebrate localities. This paper provides a preliminary assessment of the Woranso-Mille carnivoran record, a record that is of great interest given the high level of species richness of African carnivorans during the middle Pliocene. Craniodental and postcranial material of canids, lutrine mustelids, viverrids, herpestids, machairodontine and feline felids, and hyaenids has been recovered. Thus, this diverse fauna includes not only the largest carnivorans from this time period (e.g., Enhydriodon and Homotherium), but also some of the smallest, including mongooses, civets, genets, and felids, some of which represent new species. However, the diversity of small taxa does not yet approach that found in the roughly contemporaneous Upper Laetolil Beds of Tanzania. In contrast, lutrine mustelids are better represented at Woranso-Mille than at Kanapoi (Kenya) or Laetoli (Tanzania), which is to be expected given the diversity of habitats represented at these sites. While more material from these sites and others are necessary to truly understand the increased diversity within the early to middle Pliocene eastern African carnivoran guild, it is clear that the material from Woranso-Mille has the potential to fill many of the gaps in our knowledge of carnivorans during this time period.

Kolpochoerus (Mammalia: Suidae) is a suine genus represented by a number of species from Plio-Pleistocene sites in Africa. While the general trends in Kolpochoerus evolution are broadly known, gaps in the fossil record preclude an understanding of the details of its evolutionary tempo and mode. Here, we describe a new species, Kolpochoerus millensis, based on new fossil material from the Woranso-Mille and Gona sites in the Central Afar region of Ethiopia and dated to 3.5–3.8 million years ago (Ma). Third molars of K. millensis are metrically and morphologically intermediate between the early Pliocene K. deheinzelini and earliest late Pliocene K. afarensis. It appears that K. deheinzelini, K. millensis, and K. afarensis are temporally disjunct and phenetically distinguishable parts of a single evolving lineage. The recognition of these chronospecies provides additional evidence for anagenetic evolution. It demonstrates clearly the presence of transitional forms in the fossil record. The extensive and well-dated Kolpochoerus fossil record serves as one of the best documented examples of the occurrence of phyletic evolution. Moreover, K. millensis is one of the best biochronological markers in eastern Africa for the time between 3.5 and 3.8 Ma.

Recent fieldwork at Woranso-Mille, Ethiopia led to the recovery of an abundant, diverse mammalian fauna that includes remains of the early hominid Australopithecus afarensis. Proboscideans are among the taxa well sampled at the site, primarily by gnathodental specimens, dated to the mid-Pliocene interval of 3.8–3.6 Ma. These fossils document traces of the last anancine gomphotheres (Anancus ultimus) in eastern Africa and several elephant taxa. Comparative study of the elephant fossils indicates the presence of cf. Mammuthus sp. “Hadar-type,” cf. Elephas ekorensis, E. recki brumpti, and cf. Loxodonta adaurora adaurora. Proboscidean evolution in the mid-Pliocene is interesting because during this time archaic elephants were completely replaced by basal members of crown elephant lineages, taxonomic diversity was high (multiple elephant species, anancine gomphotheres, stegodonts, and deinotheres), and elephants were undergoing substantial reorganization of the craniodental masticatory apparatus, presumably in response to the spread of more open habitats and greater competition for grazing resources. The Woranso-Mille sample is important because this interval is only represented elsewhere in eastern Africa by a small number of sites, and because adaptive diversification among early crown elephants requires greater clarification. Morphometric contrasts among the fossil dentition from Woranso-Mille presage the differential success of elephant lineages in eastern Africa during the Pleistocene, providing hints about the beginnings of competitive displacement. Differences between E. recki brumpti from Woranso-Mille and the slightly younger Sidi Hakoma Member of the Hadar Formation reveal the beginnings of continuous, directional morphometric change that characterized the lineage. Reconsideration of E. recki subspecies indicates that they are arbitrary lineage divisions tied to geochronological boundaries (with utility for biochronological correlation at well sampled sites) rather than real phylogenetic entities, but does not reject monophyly or anagenetic evolution of the lineage.

Molecular studies suggest that the lineages leading to humans and chimpanzees diverged approximately 6.5–5.5 million years (Myr) ago, in the Late Miocene1,2,3. Hominid fossils from this interval, however, are fragmentary and of uncertain phylogenetic status, age, or both4,5,6. Here I report new hominid specimens from the Middle Awash area of Ethiopia that date to 5.2–5.8 Myr and are associated with a wooded palaeoenvironment7. These Late Miocene fossils are assigned to the hominid genus Ardipithecus and represent the earliest definitive evidence of the hominid clade. Derived dental characters are shared exclusively with all younger hominids. This indicates that the fossils probably represent a hominid taxon that postdated the divergence of lineages leading to modern chimpanzees and humans. However, the persistence of primitive dental and postcranial characters in these new fossils indicates that Ardipithecus was phylogenetically close to the common ancestor of chimpanzees and humans. These new findings raise additional questions about the claimed hominid status of Orrorin tugenensis8, recently described from Kenya and dated to ∼6 Myr9.

The Middle Awash study area of Ethiopia's Afar rift has yielded abundant vertebrate fossils (approximately 10,000), including several hominid taxa. The study area contains a long sedimentary record spanning Late Miocene (5.3-11.2 Myr ago) to Holocene times. Exposed in a unique tectonic and volcanic transition zone between the main Ethiopian rift (MER) and the Afar rift, sediments along the western Afar rift margin in the Middle Awash provide a unique window on the Late Miocene of Ethiopia. These deposits have now yielded the earliest hominids, described in an accompanying paper and dated here to between 5.54 and 5.77 Myr. These geological and palaeobiological data from the Middle Awash provide fresh perspectives on hominid origins and early evolution. Here we show that these earliest hominids derive from relatively wet and wooded environments that were modulated by tectonic, volcanic, climatic and geomorphic processes. A similar wooded habitat also has been suggested for the 6.0 Myr hominoid fossils recently recovered from Lukeino, Kenya. These findings require fundamental reassessment of models that invoke a significant role for global climatic change and/or savannah habitat in the origin of hominids.