This very interesting article confirms that "... morphologically the great hominoids form three clusters: Homo, the australopithecines, and the great apes. The human skull is unique and ... about equidistant from australopithecines and chimpanzees ... The australopithecine skulls resemble each other more than they resemble the apes and certainly humans ..." (Verhaegen 1996). Apparently, Homo went a very special evolutionary path, different from that of australopithecines and apes.
However, like many publications on human evolution, Pérez-Claros et al. still implicitly follow the popular, but unproven assumption that some quadrupedal apes evolved into bipedal australopithecines, some of which evolved into humans (supposedly by leaving the African forests for the plains, although primates that go from the forest to the plain typically become less vertical: the so-called "baboon paradox"): because australopithecines are argued to have been bipedal, they are believed to be human ancestors to the exclusion of chimps, bonobos and gorillas.
In fact, there are different indications that Pan and Gorilla also had more bipedal ancestors (google e.g. econiche Homo). Australopithecines typically have been found in wetlands at the time (swamp forests, lagoons, papyrus swamps etc., e.g. Reed 1997), where they - not unlike today's lowland gorillas wading in forest bais for aquatic herbaceous vegetation (AHV, google e.g. Ndoki gorilla) but more frequently - waded upright for papyrus sedges, frogbit, floating vegetation, hard-shelled invertebrates etc., and also climbed arms overhead in the branches above the swamp (google e.g. aquarboreal): this helps explain the curious combination in australopithecines of curved phalanges, vertical spine and humanlike plantigrady. Pan and Gorilla knuckle-walking then evolved in parallel from such parttime bipedally wading ancestors (arguably in response to Pleistocene cooling and drying): all African apes still regularly or occasionally wade on two legs in forest swamps in search for waterlilies, sedges etc.
Early-Pleistocene Homo on the other hand followed a unique evolution: they did not run over open plains (as commonly but illogically assumed, without even considering the possibility of wading ancestors), but dispersed intercontinentally along African and Eurasian coasts and rivers, beach-combing, diving and wading bipedally for littoral, shallow aquatic and waterside shellfish (to be opened with stone tools) and other foods rich in brain-specific nutrients (google e.g. researchGate marc verhaegen).
This early-Pleistocene "coastal dispersal model" (Munro 2010) best explains Pérez-Claros et al.'s "Neurocranium versus Face": drastic brain enlargement is typically seen in (semi)aquatic mammals, in Homo probably due to DHA-rich littoral foods such as shellfish (Cunnane 2005), and the facial reduction in Homo versus australopiths and apes is easily explained by a shift from biting-chewing to more sucking-swallowing (early-Pleistocene littoral diet of shellfish etc.).
This littoral scenario is corroborated by a lot of recent publications:
- J.Joordens, S.Munro et al. 2014 Homo erectus at Trinil on Java used shells for tool production and engraving, Nature doi 10.1038/nature13962.
- M.Verhaegen, S.Munro 2011 Pachyosteosclerosis suggests archaic Homo frequently collected sessile littoral foods, HOMO J.compar.hum.Biol. 62:237-247.
- S.Munro 2010 Molluscs as ecological indicators in palaeoanthropological contexts, PhD thesis Univ.Canberra.
- J.Joordens et al. 2009 Relevance of aquatic environments for hominins: a case study from Trinil, J.hum.Evol. 57:656-671.
- M.Gutierrez et al. 2001 Exploitation d’un grand cétacé au Paléolithique ancien: le site de Dungo V à Baia Farta, CR Acad.Sci. 332:357-362.
- K.Choi, D.Driwantoro 2007 Shell tool use by early members of Homo erectus in Sangiran, central Java, Indonesia: cut mark evidence, J.archaeol.Sci. 34:48-58.
- S.Cunnane 2005 Survival of the fattest: the key to human brain evolution, World Scient.Publ.Comp.
- M.Vaneechoutte et al. eds 2011 Was Man more aquatic in the past? eBook Bentham Sci.Publ.
- M.Verhaegen 1996 Morphological distance between australopithecine, human and ape skulls, Hum.Evol.11:35-41.
- K.Reed 1997 Early hominid evolution and ecological change through the African Plio-Pleistocene, JHE 32:289-322.
- P.Rhys Evans et al. eds 2013-2014 Human Evolution conference London May 2013 proceedings, special editions Hum.Evol.28 & 29.