Comparative description and taxonomic affinity of 3.7-million-year-old hominin mandibles from Woranso-Mille (Ethiopia).

Fossil discoveries of early Australopithecus species from Woranso-Mille have played a significant role in improving our understanding of mid-Pliocene hominin evolution and diversity. Here, we describe two mandibles with dentitions, recovered from sediments immediately above a tuff radiometrically dated to 3.76 ± 0.02 Ma, and assess their taxonomic affinity. The two mandibles (MSD-VP-5/16 and MSD-VP-5/50) show morphological similarities with both Australopithecus anamensis and Australopithecus afarensis. Some of the unique features that distinguish Au. anamensis from Au. afarensis are present in the mandibles, which also share a few derived features with Au. afarensis. Their retention of more Kanapoi Au. anamensis-like traits, compared to the fewer derived features they share with Au. afarensis, and the presence of Au. anamensis at Woranso-Mille in 3.8-million-year-old deposits, lends support to their assignment to Au. anamensis. However, it is equally arguable that the few derived dentognathic features they share with Au. afarensis could be taxonomically more significant, making it difficult to conclusively assign these specimens to either species. Regardless of which species they are assigned to, the mosaic nature of the dentognathic morphology and geological age of the two mandibles lends further support to the hypothesized ancestor-descendant relationship between Au. anamensis and Au. afarensis. However, there is now limited fossil evidence indicating that these two species may have overlapped in time. Hence, the last appearance of Au. anamensis and first appearance of Au. afarensis are currently unknown. Recovery of Australopithecus fossils from 4.1 to 3.8 Ma is critical to further address the timing of these events.

New Pliocene hominin remains from the Leado Dido'a area of Woranso-Mille, Ethiopia.

Fossiliferous deposits at Woranso-Mille span the period when Australopithecus anamensis gave rise to Australopithecus afarensis (3.8-3.6 Ma) and encompass the core of the A. afarensis range (ca. 3.5-3.2 Ma). Within the latter period, fossils described to date include the intriguing but taxonomically unattributed Burtele foot, dentognathic fossils attributed to Australopithecus deyiremeda, and one specimen securely attributed to A. afarensis (the Nefuraytu mandible). These fossils suggest that at least one additional hominin lineage lived alongside A. afarensis in the Afar Depression. Here we describe a collection of hominin fossils from a new locality in the Leado Dido'a area of Woranso-Mille (LDD-VP-1). The strata in this area are correlated to the same chron as those in the Burtele area (C2An.3n; 3.59-3.33 Ma), and similar in age to the Maka Sands and the Basal through lower Sidi Hakoma Members of the Hadar Formation. We attribute all but one of the LDD hominin specimens to A. afarensis, based on diagnostic morphology of the mandible, maxilla, canines, and premolars. The LDD specimens generally fall within the range of variation previously documented for A. afarensis but increase the frequency of some rare morphological variants. However, one isolated M3 is extremely small, and its taxonomic affinity is currently unknown. The new observations support previous work on temporal trends in A. afarensis and demonstrate that the large range of variation accepted for this species is present even within a limited spatiotemporal range. The value added with this sample lies in its contribution to controlling for spatiotemporal differences among site samples in the A. afarensis hypodigm and its contemporaneity with non-A. afarensis specimens at Woranso-Mille.

Age and context of mid-Pliocene hominin cranium from Woranso-Mille, Ethiopia.

A fossil hominin cranium was discovered in mid-Pliocene deltaic strata in the Godaya Valley of the northwestern Woranso-Mille study area in Ethiopia. Here we show that analyses of chemically correlated volcanic layers and the palaeomagnetic stratigraphy, combined with Bayesian modelling of dated tuffs, yield an age range of 3.804 ± 0.013 to 3.777 ± 0.014 million years old (mean ± 1σ) for the deltaic strata and the fossils that they contain. We also document deposits of a perennial lake beneath the deltaic sequence. Mammalian fossils associated with the cranium represent taxa that were widespread at the time and data from botanical remains indicate that the vegetation in the lake and delta catchment was predominantly dry shrubland with varying proportions of grassland, wetland and riparian forest. In addition, we report high rates of sediment accumulation and depositional features that are typical of a steep topographic relief and differ from younger Woranso-Mille fossil localities, reflecting the influence of active rift processes on the palaeolandscape.

Dentognathic remains of Australopithecus afarensis from Nefuraytu (Woranso-Mille, Ethiopia): Comparative description, geology, and paleoecological context.

Australopithecus afarensis is the best-known and most dimorphic species in the early hominin fossil record. Here, we present a comparative description of new fossil specimens of Au. afarensis from Nefuraytu, a 3.330-3.207 million-years-old fossil collection area in the Woranso-Mille study area, central Afar, Ethiopia. These specimens include NFR-VP-1/29, one of the most complete mandibles assigned to the species thus far and among the largest mandibles attributed to Au. afarensis, likely representing a male individual. NFR-VP-1/29 retains almost all of the distinctive archaic features documented for Au. afarensis. These features include a posteriorly sloping symphysis, a low and rounded basally set inferior transverse torus, anterosuperiorly opening mental foramen, a lateral corpus hollow bound anteriorly by the C/P3 jugae and posteriorly by the lateral prominence, and the ascending ramus arising high on the corpus. Dental morphology and metrics of the Nefuraytu specimens also falls within the range of Au. afarensis. The presence of this species at Woranso-Mille between 3.330 and 3.207 million years ago confirms the existence of this species in the area in close spatial and temporal proximity to other middle Pliocene hominin taxa such as the one represented by the Burtele foot (BRT-VP-2/73) and the recently named species Australopithecus deyiremeda. This has important implications for our understanding of middle Pliocene hominin diversity.

Tephrostratigraphy of the Waki-Mille area of the Woranso-Mille paleoanthropological research project, Afar, Ethiopia.

Tephra geochemistry and (40)Ar/(39)Ar geochronology are reported for the Waki-Mille area in the northwestern part of the Woranso-Mille paleoanthropological project area in the west central Afar region of Ethiopia. Previous studies documented dentognathic fossils that are morphologically intermediate between Australopithecus anamensis and Australopithecus afarensis and some that are attributed to Australopithecus afarensis. Additional dentognathic remains from the study area were assigned to the newly identified species Australopithecus deyiremeda. These fossil hominin taxa were recovered from volcanic and sedimentary strata containing tuffs ranging in age from more than 3.77 million years ago (Ma) to less than 3.469 Ma. One of the tuffs was correlated based on geochemistry, feldspar mineralogy, and age to the Lokochot Tuff of the Omo-Turkana Basin of southern Ethiopia and Kenya. Variations in major and minor element abundances in volcanic glass demarcate ten geochemically distinct tuffs and tuff sequences, including three that are geochemically similar to widespread regional tuffs, specifically the Lomogol, Lokochot, and ß- Tulu Bor/Sidi Hakoma tuffs. A new (40)Ar/(39)Ar age for the Waki Tuff, which is geochemically similar to the Lomogol Tuff, is 3.664 ± 0.016 Ma. Other tuffs in the Waki-Mille area are geochemically dissimilar to regional tuffs documented to date. Identification of tuffs based on character, stratigraphic position, and geochemistry refines local stratigraphic correlations and delineates the geographic distributions of precisely dated fossiliferous levels within the Waki-Mille area.

Dietary change among hominins and cercopithecids in Ethiopia during the early Pliocene.

The incorporation of C4 resources into hominin diet signifies increased dietary breadth within hominins and divergence from the dietary patterns of other great apes. Morphological evidence indicates that hominin diet became increasingly diverse by 4.2 million years ago but may not have included large proportions of C4 foods until 800 thousand years later, given the available isotopic evidence. Here we use carbon isotope data from early to mid Pliocene hominin and cercopithecid fossils from Woranso-Mille (central Afar, Ethiopia) to constrain the timing of this dietary change and its ecological context. We show that both hominins and some papionins expanded their diets to include C4 resources as early as 3.76 Ma. Among hominins, this dietary expansion postdates the major dentognathic morphological changes that distinguish Australopithecus from Ardipithecus, but it occurs amid a continuum of adaptations to diets of tougher, harder foods and to committed terrestrial bipedality. In contrast, carbon isotope data from cercopithecids indicate that C4-dominated diets of the earliest members of the Theropithecus oswaldi lineage preceded the dental specialization for grazing but occurred after they were fully terrestrial. The combined data indicate that the inclusion of C4 foods in hominin diet occurred as part of broader ecological changes in African primate communities.

New species from Ethiopia further expands Middle Pliocene hominin diversity.

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.

A new hominin foot from Ethiopia shows multiple Pliocene bipedal adaptations.

A newly discovered partial hominin foot skeleton from eastern Africa indicates the presence of more than one hominin locomotor adaptation at the beginning of the Late Pliocene epoch. Here we show that new pedal elements, dated to about 3.4 million years ago, belong to a species that does not match the contemporaneous Australopithecus afarensis in its morphology and inferred locomotor adaptations, but instead are more similar to the earlier Ardipithecus ramidus in possessing an opposable great toe. This not only indicates the presence of more than one hominin species at the beginning of the Late Pliocene of eastern Africa, but also indicates the persistence of a species with Ar. ramidus-like locomotor adaptation into the Late Pliocene.

An early Australopithecus afarensis postcranium from Woranso-Mille, Ethiopia.

Only one partial skeleton that includes both forelimb and hindlimb elements has been reported for Australopithecus afarensis. The diminutive size of this specimen (A.L. 288-1 ["Lucy"]) has hampered our understanding of the paleobiology of this species absent the potential impact of allometry. Here we describe a large-bodied (i.e., well within the range of living Homo) specimen that, at 3.58 Ma, also substantially antedates A.L. 288-1. It provides fundamental evidence of limb proportions, thoracic form, and locomotor heritage in Australopithecus afarensis. Together, these characteristics further establish that bipedality in Australopithecus was highly evolved and that thoracic form differed substantially from that of either extant African ape.

New hominid fossils from Woranso-Mille (Central Afar, Ethiopia) and taxonomy of early Australopithecus.

The phylogenetic relationship between Australopithecus anamensis and Australopithecus afarensis has been hypothesized as ancestor-descendant. However, the weakest part of this hypothesis has been the absence of fossil samples between 3.6 and 3.9 million years ago. Here we describe new fossil specimens from the Woranso-Mille site in Ethiopia that are directly relevant to this issue. They derive from sediments chronometrically dated to 3.57-3.8 million years ago. The new fossil specimens are largely isolated teeth, partial mandibles, and maxillae, and some postcranial fragments. However, they shed some light on the relationships between Au. anamensis and Au. afarensis. The dental morphology shows closer affinity with Au. anamensis from Allia Bay/Kanapoi (Kenya) and Asa Issie (Ethiopia) than with Au. afarensis from Hadar (Ethiopia). However, they are intermediate in dental and mandibular morphology between Au. anamensis and the older Au. afarensis material from Laetoli. The new fossils lend strong support to the hypothesized ancestor-descendant relationship between these two early Australopithecus species. The Woranso-Mille hominids cannot be unequivocally assigned to either taxon due to their dental morphological intermediacy. This could be an indication that the Kanapoi, Allia Bay, and Asa Issie Au. anamensis is the primitive form of Au. afarensis at Hadar with the Laetoli and Woranso-Mille populations sampling a mosaic of morphological features from both ends. It is particularly difficult to draw a line between Au. anamensis and Au. afarensis in light of the new discoveries from Woranso-Mille. The morphology provides no evidence that Au. afarensis and Au. anamensis represent distinct taxa.