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Fossil Friday: Homo rudolfensis, Another Contentious Homo

Photo credit: Gunnar Creutz, CC BY-SA 4.0 , via Wikimedia Commons.

Last week for Fossil Friday I posted some musings about Homo habilis and its controversial attribution to our genus. This week we will have a look at another disputed relative, Homo rudolfensisAlexeev (1986) described the new species Homo (Pithecanthropus) rudolfensis from a single skull (KNM-ER 1470) discovered in 1972 by Richard Leakey at the 1.9 million year old Koobi Fora locality of the Turkana Lake (formerly known as Lake Rudolf) basin in East Africa (also see Wood 1999). The material was previously considered to be conspecific with Homo habilis, which is a hypothesis still entertained by some modern experts. However, the skull differs from Homo habilis in its flat face and larger brain volume as well as the more robust-australopithecine-like cheek teeth. Unfortunately, no associated postcranial remains are known yet (Berger et al. 2015), so that the most distinctive characters of the genus Homo and those for bipedal gait are unknown (Tuttle 2006: 253).

A New Digital Reconstruction

As for Homo habilis, Wood & Collard (1999a1999b2001) and Collard & Wood (2007, 2015) indeed advocated for transferring H. rudolfensis to the genus Australopithecus, which had already been suggested by other researchers (i.e., Walker 1976 and Lieberman et al. 1996). Walker & Shipman (1996) pointed out that “1470 might have a big braincase, but morphologically it was just an australopithecine.” A new digital reconstruction of the skull by Bromage et al. (2008) showed that it was somewhat less flat and the brain volume somewhat smaller, which made it even more similar to australopithecine skulls. Nevertheless, the latter study retained this species in the genus Homo. A co-author of this study was German paleoanthropologist Friedemann Schrenk, who at my university, Tübingen, was known by the sneering nickname the “Möllemann of German paleontology.” That was because he shared a notorious proclivity for PR stunts and media hype with the late German politician Jürgen Möllemann. He discovered a hominin mandible (UR 501) in Malawi, which he attributed to Homo rudolfensis and with an estimated age of 2.4 million years this would be much older than the holotype. Of course, publications on an early Homo make for much more sensational press releases than just another ape-man.

Anyway, Leakey et al. (2001) and Lieberman (2001) noted several striking similarities in the facial architecture of the newly described hominin Kenyanthropus platyops and the 1.6 million year younger H. rudolfensis, who could be a late survivor of the australopithecine-like Kenyanthropus lineage rather than an early Homo. The phylogenetic analysis by Cameron & Groves (2004) strongly confirmed the reclassification as Kenyanthropus rudolfensis by Cameron (2003)Cela-Conde & Ayala (2003) agreed that Homo rudolfensis (and H. habilis) should be grouped with Kenyanthropus platyops, but instead proposed to include all three within the genus Homo. That would place the origin of our genus 3.5 million years ago, in stark contradiction to all other experts and the unequivocal empirical evidence from the fossil record. 

Four Hypotheses

Prat (2007) compared the four suggested alternative hypotheses: H. rudolfensis is conspecific with Homo habilisH. rudolfensis and H. habilis are both distinct species of Homo; both species belong to the genus Australopithecus; or H. rudolfensis belongs to the genus Kenyanthropus. Prat came to the conclusion that Homo rudolfensis is distinct but her cladistic analysis suffers from several flaws. This is evident from the fact that the inclusion of the holotype of Kenyanthropus platyops did not just influence the polarity of some characters but produced a totally different tree topology with hardly any similarity to the tree recovered by excluding this taxon. The confidence level in any such highly unstable analyses should be very low for reasonable and unbiased scientists. However, having two early species of Homo is of course a highly desirable result for evolutionist paleoanthropologists, and so it is hardly surprising that almost all subsequent publications maintained the attribution of these two species to the genus Homo.

Awaiting Better Evidence

More recently, a more ancient origin of our genus has indeed been claimed by the discovery of a 2.8 million year old human mandible at Ledi-Geraru in the Afar region of Ethiopia, which was attributed to an early Homo (Villmoare et al. 2015). But this fossil combines primitive australopithecine traits with more derived features of later Homo, and it also suffers from the absence of any other cranial and postcranial characters that could support this claim. Considering the checkered history of grandiose claims and controversies in paleoanthropology, some caution may be wise until more and better evidence is found.


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