Response to Comment on “Early Homo at 2.8 Ma from Ledi-Geraru, Afar, Ethiopia”

Abstract

Hawks et al. argue that our analysis of Australopithecus sediba mandibles is flawed and that specimen LD 350-1 cannot be distinguished from this, or any other, Australopithecus species. Our reexamination of the evidence confirms that LD 350-1 falls outside of the pattern that A. sediba shares with Australopithecus and thus is reasonably assigned to the genus Homo.H awks et al.(1) claim that we misinterpreted the mandibular anatomy of the Malapa hominins and, as a result, failed to satisfactorily distinguish the LD 350-1 jaw from Australopithecus. We stand by our assessments of the mandibular and dental anatomy of A. sediba. On the right side of the MH2 mandibular corpus, the inferior border is damaged posterior to mid-M 2 , but any reasonable estimate of "minimum corpus depth" [as defined in (2); Hawks et al. do not specify their method] below M 2 is 2.5 to 3.5 mm less than the depth below P 3 . The left side of the MH2 corpus [specimen UW88-55 (3)] is also preserved, however, and is undamaged from the M 1 level to posterior to M 3 . The inferior margin of the damaged right corpus (4) can be inferred by photographically superimposing the left side onto the right (Fig. 1), which reveals the primitive (australopith-like) height relationships of the corpus, deeper anteriorly and considerably less so posteriorly. On a cast of MH2, we measure minimum lingual corpus height at left M 2 as 26.6 mm and at right P 3 as 30.3 mm.With regard to the juvenile MH1 mandible (M 3 unerupted), our data on chimpanzees and A. afarensis show that, although corpus depth does indeed change with emergence of the final molar, the relative anterior to posterior depth (P 3 :M 2 ) is essentially stable from the time of M 2 emergence. Therefore, in MH1, the clear discrepancy in corpus depth [see figure 1 in (3)] is unlikely to have changed substantially with the attainment of adulthood, confirming our assessment of a posteriorly shallowing corpus in the Malapa hominins, as commonly seen in Australopithecus.Hawks et al. argue that the orientation of the mental foramen in MH2 is lateral, rather than anterior, as we described. Without prejudicing our assessment of MH2, we note that a lateral orientation of the foramen fits the description of A. africanus [as noted in (2)], whereas a clear posterior opening of the foramen into a short groove on the corpus, as in LD 350-1, is typically seen only in Homo among nonrobust early hominins. With regard to the root of the ascending ramus, our definition [as noted in the legend of figure S7 in (2)] is the point at which the anterior ramus margin becomes independent of the corpus, which on MH2 clearly occurs at M 2 /M 3 , as we described (Fig. 1). It is the concave vertical segment of the anterior margin that leaves the M 3 visible in lateral view, not an extreme posterior origin of the margin as in LD 350-1.The flaring buccal face of the molars in MH1, the standard condition in Australopithecus, may or not have been present in MH2. Heavy occlusal wear, to the point of substantially reducing crown height a...

A Phylogenetic Networks perspective on reticulate human evolution

“…First, the publication of the Homo naledi remains ( Berger et al., 2015 ) rekindled the questions of what constitutes this genus and from which ancestral morphotype it originates; some critics proclaiming that this new species is an example of artificial species inflation in paleoanthropology ( Randolph-Quinney, 2015 ). Second, the discovery of early Homo (2.8 Ma) from Ledi-Geraru ( Villmoare et al., 2015a ) was the object of criticisms by competing researchers ( Hawks et al., 2015 ; Villmoare et al., 2015b ). It is clear that the use of the term “early Homo,” given the multiplicity of fossils it encompasses (non- Homo erectus specimens such as Homo sp.…”

“What’s in a Name?” <i>The Taxonomy & Phylogeny of Early</i> Homo

“…Nevertheless, LD 350-1 has been conservatively assigned to Homo species indeterminate pending the discovery of additional fossils (Villmoare et al, 2015a; see also Hawks et al, 2015 andVillmoare et al, 2015b).…”