The Emergence of the Rudolfensis Group

In the 1970s, a remarkable skull, KNM-ER 1470 (Figure 4.6) —known to the general public simply as "skull 1470"—was discovered at Koobi Fora, in northern Kenya, in deposits we now know to be from 1.89 Ma (R.E.F. Leakey, 1973a, 1973b, 1974; Day et al., 1975; B.A. Wood, 1976, 1991). It was originally allocated to Homo habilis, the earliest and most primitive species of our own genus. Doubts began to grow in the 1980s that 1470 really was Homo habilis (it was just too different from the acknowledged specimens of that species from Olduvai Gorge in Tanzania). By the late 1980s there was a general acquiescence that it should be placed in a different species, Homo rudolfensis (Alexeev, 1986), and some other specimens from Koobi Fora were placed in the same species. During the 1990s, some researchers began to question whether it was Homo at all (D.E. Lieberman et al., 1988; partly B.A. Wood, 1991). By the late 1990s, it was being widely asked what this "rudolfensis" actually was and where it came from.

Figure 4.6 ► Frontal view of Kenyanthropus rudolfensis specimen KNM-ER 1470.

The recent discovery of Kenyanthropus platyops has supplied a possible answer: Here, in this contemporary of Praeanthropus afarensis, was the by-now eagerly sought ancestor to rudolfensis! If this is indeed the answer, then of course Homo rudolfensis should be transferred out of Homo and placed within its ancestor's genus, Kenyanthropus, and called Kenyanthropus rudolfensis (see D.E. Lieberman, 2001; partly M.G. Leakey et al., 2001). Its removal from Homo would vindicate the arguments put forward originally by Alan Walker, who in the 1970s argued that 1470 was no more than a slightly more derived species of Australopithecus, with a larger brain (Walker, 1976; Walker & Shipman, 1996; D.E. Lieberman et al., 1996).

Our phylogenetic analyses (discussed in the next chapter) consistently indicate that the rudolfensis group shares a sister-group relationship with Kenyanthropus platyops. If this truly reflects the evolutionary history of this hominin, it should be considered a species of this genus. These same analyses also indicate that Kenyanthropus shared a sister-group relationship with the species of Homo, indicating that they, like Paranthropus and Australopithecus, are hominins, as opposed to mere hominids.

This scheme confirms that those more than 3-million-year-old species usually allocated to Australopithecus do not share a particularly close relationship with the later hominins and probably had little if anything directly to do with their evolution. It also indicates that at least three genera coexisted in Africa around 2.3 Ma: Paranthropus, Kenyanthropus, and early Homo. They may have last shared a common ancestor as early as 3.5 million years ago.

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