THE MORPHOLOGY OF KNM-ER1805: A Reconsideration of an Enigmatic Specimen

Abstract

In the past, KNM-ER 1805 has been designated as a paratype for Homo erectus, H. ergaster, H. habilis, and H. rudolfensis. Based on its stratigraphic position within the KBS layer (~1.85mya) of the Koobi Fora Formation, this specimen can be temporally associated with all of these taxa, and with Paranthropus boisei. Although the majority of researchers attribute KNM-ER 1805 to the genus Homo, some suggest it might be more appropriately allocated to Paranthropus or Australopithecus, thus this issue remains unresolved. This study examines 27 metric and 122 non-metric cranial and mandibular features of several groups of African Plio-Pleistocene hominins to determine the phylogenetic status of KNM-ER 1805 relative to contemporary hominin taxa. It employs multivariate exploration techniques (principal components and discriminant function analyses) and phylogeny reconstruction methods: CONTML for continuous characters as well as PAUP* (parsimony) and MrBayes (Bayesian analysis) for discrete characters. Results of the multivariate analyses reveal an association between KNM-ER 1805 and specimens allocated to A. africanus, H. habilis, and H. ergaster. Cladograms produced from the phylogenetic analyses show little resolution, but in each instance where a clear separation between Homo and the australopithecines (Paranthropus and Australopithecus) is revealed, KNM-ER 1805 consistently groups with the australopithecines. These results suggest KNM-ER 1805 is not a typical specimen of H. habilis/rudolfensis or H. erectus/ergaster, despite the fact that it has been cited as a paratype for each of these taxa. Furthermore, these results suggest the affinity of this enigmatic specimen may not lie with the genus Homo at all.