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.bipedality | human evolution | upright walking | hominid | thorax

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.

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Supplementary Note 1. MRD-VP-1/1: Detailed description of discovery and preservation 1.1. Recovery. MRD was recovered from the surface in two major pieces. The facial component was found on February 10, 2016 by an Afar worker (Ali Bereino) at a place locally known as "Miro Dora" (11º32'59.5" N; 40º27'54.6" E). The rest of the cranium was found on the same day by YHS ca. 3m northeast of the face. After the discovery of the two major pieces (the face and the neurocranium), a sieving operation was carried out to recover more pieces that might have broken away from the specimen. The team first crawled the area in the immediate vicinity of the two major pieces and then surface swept an area of ca. 30 m 2. While the specimen eroded out from a sandstone horizon (based on the matrix adhered to it) and the amount of loose original sediment on top of it was minimal, the main area that had to be sieved was covered by up to 30 cm deep goat droppings piled up for many years, indicating that there was a lot of animal movement in the area and some of the fragments of MRD-VP-1/1 may have been destroyed by trampling. The sieving operation resulted in the recovery of many fragments including two pieces of the left zygomatic bone. The larger piece constituted most of the malar region including the frontal process and some part of the frontal bone at the superolateral corner of the orbit. The other piece was a small fragment that joined to the bigger piece at the anterior origin of the zygomatic arch. One small but critical piece, that joined the left zygomatic bone with the frontal, was also found from the sieve. Other pieces that were found as a result of the sieving operation include a small fragment of the left zygomatic arch, which joined the temporal bone at the posterior end of the arch. Two more fragments of the zygomatic arch from mid-section were also recovered even though their position on the arch is unknown. A larger piece from the base of the right zygomatic was also recovered. This fragment has the entire masseteric origin preserved but did not join the * Landmarks identifiable on the left and right sides. ** Semilandmarks identified on the curves. * Landmarks identifiable on the left and right sides. ** Semilandmarks identified on the curves.

Recent discoveries of multiple middle Pliocene hominins have raised the possibility that early hominins were as speciose as later hominins. However, debates continue to arise around the validity of most of these new taxa, largely based on poor preservation of holotype specimens, small sample size, or the lack of evidence for ecological diversity. A closer look at the currently available fossil evidence from Ethiopia, Kenya, and Chad indicate that Australopithecus afarensis was not the only hominin species during the middle Pliocene, and that there were other species clearly distinguishable from it by their locomotor adaptation and diet. Although there is no doubt that the presence of multiple species during the middle Pliocene opens new windows into our evolutionary past, it also complicates our understanding of early hominin taxonomy and phylogenetic relationships.If one looks back over the controversies of human evolution, they have one element in common: new discoveries, theories, methods came along which no one in the controversy anticipated. The "facts" changed, and consequently people were not right or wrong in any simple way.S. L. Washburn and R. L. Ciochon, 1974 (1) New fossil discoveries and analytical methods that have proliferated during the last few decades have fundamentally changed how we study and interpret hominin fossils and understand human evolution. The discovery and subsequent naming of Australopithecus afarensis in the late 1970s was one of the major milestones in paleoanthropology (2). Its discovery not only pushed the record of hominins to earlier than 3 million years ago (Ma) (2), but also demonstrated the antiquity of human-like bipedality (3). However, the taxonomic homogeneity of the Au. afarensis hypodigm has been questioned since its naming (4-7), even though the Hadar fossil sample appears to be no more variable than other living ape species (8-11). A consensus emerged during the 1980s in which Au. afarensis, dated to between 3.7 and 2.9 Ma, was considered to be the sole early hominin species older than 3 Ma, largely supported by the lack of fossil evidence to indicate otherwise.When Australopithecus bahrelghazali was named in 1995 based on an approximately 3.5-Ma partial mandible from Chad (12), it was quickly dismissed as a geographic variant of Au. afarensis (13-15). The initial descriptions of Ardipithecus ramidus (16) and Australopithecus anamensis (17), followed by the naming of even earlier hominin species, such as Orrorin tugenensis (18), Ardipithecus kadabba (19,20), and Sahelanthropus tchadensis (21), extended the antiquity of our lineage as far back as >6 Ma. These early hominins initially appeared to show no temporal or spatial overlap, and hence reinforced the idea that the early phases of hominin evolution were characterized by phenetic continuity and phyletic gradualism, with only one hominin species existing in a region at any given time >3 Ma (e.g., ref. 22; see discussions below).The discovery of the Burtele partial foot from Ethiopia (23), the naming of Kenyan...