Australopithecus afarensis endocasts suggest ape-like brain organization and prolonged brain growth

Did A. afarensis herald the rise of long childhoods in hominids, as Gunz et al. suggests?

This is unlikely, since Gunz et al. showed that the endocast of afarensis had an apelike brain organization.

Equally likely, A. afarensis might simply have heralded the rise of longer childhoods in gorillas: gorillas mature more slowly than chimps do.

In fact, most East-African australopithecine fossils (afarensis, aethiopicus, boisei) have a lot of gorilla-like features, and the more recent fossils (aethiopicus-boisei) seem to have even more gorilla features than the earlier ones (afarensis), e.g.

- Ryan & Johanson 1989: "Incisal dental microwear in A. afarensis is most similar to that observed in Gorilla".

- Johanson & Edey 1981:351: The composite skull reconstructed mostly from A.L.333 specimens "looked very much like a small female gorilla".

- Walker cs 1986: "Other primitive features found in KNM-WT 17000: very small cranial capacity; low posterior profile of the calvaria; nasals extended far above the frontomaxillar suture and well onto an uninflated glabella; and extremely convex inferolateral margins of the orbits such as found in some gorillas."

- Kennedy 1991: As for the maximum parietal breadth and the biauriculare in O.H.5 and KNM-ER 406 "the robust australopithecines have values near the Gorilla mean: both the pongids and the robust australopithecines have highly pneumatized bases."

- Robinson 1960: In O.H.5, "the curious and characteristic features of the Paranthropus skull ... parallel some of those of the gorilla."

- Leakey & Walker 1988: The A.boisei "lineage has been characterized by sexual dimorphism of the degree seen in modern Gorilla for the length of its known history."

- Beynon & Wood 1986: A. boisei teeth showed "a relative absence of prism decussation"; among extant hominoids, "Gorilla enamel showed relatively little decussation."

The references can be found in my 1994 paper "Australopithecines: ancestors of the African apes?" in Human Evolution 9:121-139.

These results were fully confirmed mathematically in my 1996 paper: "Morphological distance between australopithecine, human and ape skulls" in Human Evolution 11:35-41, which concluded: "This comparison of 37 craniodental characters of fossil and living apes and humans yields no indication that any of the australopithecine species has evolved in the human direction. South African australopithecine skulls are morphologically closest to the chimpanzee among the living hominoids, and A. boisei is closest to the gorilla among the living hominoids."
These conclusions have been confirmed by publications on australopithecine fossils after 1996.

All 'humanlike' features in australopithecines are not derived-human, but primitive-hominid or even primitive-hominoid, e.g. short canines and thick molar enamel are already seen in many Mio-Pliocene hominoid fossils. And most if not all Mio-Pliocene hominoids appear to have had vertical lumbar spines, not for running bipedally over the open African plains as still often assumed, but simply for wading bipedally and for climbing arms overhead in the swamp and flooded forests and wetlands, where Mio-Pliocene hominoids typically fossilized, much like extant bonobos and lowland gorillas still do regularly in search for aquatic herbaceous vegetation (AHV), google e.g. "bonobo wading" and "gorilla bai" illustrations.

For a more extensive discussion and references, please see my 2013 paper "The aquatic ape evolves: common misconceptions and unproven assumptions about the so-called Aquatic Ape Hypothesis " in Human Evolution 28:237-266, or for an update google e.g. "Lucy was no human ancestor 2020 verhaegen".