Earliest Homo debate

The taxonomic status of the Chemeron temporal (KNM-BC 1)

Temporal bone morphology, as part of the basicranium, is commonly used in systematic evaluation of early hominid fossils. When an isolated right temporal bone, KNM-BC 1 (the Chemeron temporal) was discovered in the Baringo Basin, Kenya, Tobias (1967 a, Nature215, 476-480), citing ambiguity of characters, hesitated to place the specimen generically, attributing the fossil only to Hominidae gen. et sp. indet. Since that discovery, the early hominid sample has grown considerably and comparisons with this expanded dataset led Hill et al. (1992 a, Nature355, 719-722) to revise the placement of KNM-BC 1 including it within the genus Homo. This revision was possible due to the increased number of hominid fossil specimens from the late Pliocene/early Pleistocene, most notably members of the genus Homo. A thorough investigation into the utility of the temporal bone in hominid systematics shows that many features, as currently used in the literature, demonstrate high levels of variation thus questioning their phyletic valence. It is shown, however, that the temporal bone still contains useful systematic information. A detailed anatomical description of KNM-BC 1 is provided and, when discussed in the context of temporal bone features provided, affirms the conclusion of Hill et al. (1992 a) and places the fossil within the genus Homo.

A reappraisal of early hominid phylogeny

We report here on the results of a new cladistic analysis of early hominid relationships. Ingroup taxa included Australopithecus afarensis, Australopithecus africanus, Australopithecus aethiopicus, Australopithecus robustus, Australopithecus boisei, Homo habilis, Homo rudolfensis, Homo ergaster and Homo sapiens. Outgroup taxa included Pan troglodytes and Gorilla gorilla. Sixty craniodental characters were selected for analysis. These were drawn from the trait lists of other studies and our own observations. Eight parsimony analyses were performed that differed with respect to the number of characters examined and the manner in which the characters were treated. Seven employed ordered characters, and included analyses in which (1) taxa that were variable with respect to a character were coded as having an intermediate state, (2) characters with variable states in any taxon were excluded; (3) a variable taxon was coded as having the state exhibited by the majority of its hypodigm, (4) variable taxa were coded as missing data for that character, (5) some characters were considered irreversible, (6) masticatory characters were excluded, and (7) characters whose states were unknown in some taxa were excluded. In the final analysis, (8) all characters were unordered. All analyses were performed using PAUP 3.0s. Despite the fact that the eight analyses differed with respect to methodology, they produced several consistent results. All agreed that the "robust" australopithecines form a clade, A. afarensis is the sister taxon of all other hominids, and the genus Australopithecus, as conventionally defined, is paraphyletic. All eight also supported trees in which A. africanus is the sister taxon of a joint Homo+ "robust" clade, although in one analysis an equally parsimonious topology found A. africanus to be the sister of the "robust" species. In most analyses, the relationships of A. africanus and H. habilis were unstable, in the sense that their positions vary in trees that are marginally less parsimonious than the favored one. Trees in which "robust" australopithecines are paraphyletic were found to be extremely unparsimonious.