MORPHOMETRIC VARIATION IN PLIOPLEISTOCENE HOMINID DISTAL HUMERI

The magnitude and meaning of morphological variation among Plio-Pleist ocene hominid distal humeri have been recurrent points of disagreement among paleoanthropologists. Some researchers have found noteworthy di fferences among fossil humeri that they believe merit taxonomic separa tion, while others question the possibility of accurately sorting thes e fossils into different species and/or functional groups. Size and sh ape differences among fossil distal humeri are evaluated here to deter mine whether the magnitude and patterns of these differences can be ob served within large-bodied, living hominoids. Specimens analyzed in th is study have been assigned to various taxa (Australopithecus afarensi s, A, africanus, A. anamensis, Paranthropus, and early Homo) and inclu de AL 288-1m, AL 288-1s, AL 137-48a, AL 322-1, Gombore IB 7594, TM 151 7, KNM-ER 739, KNM-ER 1504, KMN-KP 271 (Kanapoi), and Stw 431. Five ex tant hominoid populations are sampled to provide a standard by which t o consider differences found between the fossils, including two modern human groups (Native American and African American), one group of Pan troglodytes, and two subspecies of Gorilla gorilla (G. g. beringei, G . g. gorilla). All possible pairwise d values (average Euclidean dista nces) are calculated within each of the reference populations using an exact randomization procedure. This is done using both raw linear mea surements as well as scale-free shape data created as ratios of each m easurement to the geometric mean. Differences between each pair of fos sil humeri are evaluated by comparing their d values to the distributi on of d values found within each of the reference populations. Princip al coordinate analysis and an unweighted pair group method with arithm etic averages (UPGMA) cluster analysis are utilized to further assess similarities and differences among the fossils. Finally, canonical var iates analysis and discriminant analysis are employed using all homino id samples in order to control for correlations among variables and to identify those variables that discriminate among groups; possible aff inities of individual fossils with specific extant species are also ex amined. The largest size differences, those between the small Hadar sp ecimens and the two largest fossils (KNM-ER 739, IB 7594), can be acco mmodated easily within the ranges of variation of the two Gorilla samp les, but are extreme relative to the other reference samples. The d va lues between most of the fossils based on shape data, with the notable exception of those associated with KNM-ER 739 and KNM-ER 1504, can be sampled safely within all five reference samples. Subsequent analyses further support the inference that KNM-ER 739 and KNM-ER 1504 are dif ferent from the other hominid humeri and possess a unique total morpho metric pattern. In overall shape, the distal humeri of the other fossi ls (non-Koobi Fora) are most similar to living chimpanzees. The distal humerus of Paranthropus from Kromdraai (TM 1517e) is most similar to one of the Hadar specimens of A. afarensis (AL 137-48a), whereas the f irst specimen of A. africanus from Sterkfontein (Stw 431) is not close ly linked to any of the other australopithecines. The A. anamensis hum erus from Kanapoi exhibits no special affinities to A. afarensis or to modern humans. (C) 1996 Wiley-Liss, Inc.