Morphometric variation in Plio‐Pleistocene hominid distal humeri

The magnitude and meaning of morphological variation among Plio-Pleistocene hominid distal humeri have been recurrent points of disagreement among paleoanthropologists. Some researchers have found noteworthy differences among fossil humeri that they believe merit taxonomic separation, while others question the possiblity of accurately sorting these fossils into different species and/or functional groups. Size and shape differ- ences among fossil distal humeri are evaluated here to determine whether the magnitude and patterns of these differences can be observed within large- bodied, living hominoids. Specimens analyzed in this study have been assigned to various taxa (Aus- tralopithecus afarensis, A. africanus, A. anamensis, Paranthropus, and early Homo) and include AL 288-1m, AL 288-ls, AL 137-48a, AL 322-1, Gombork IB 7594, TM 1517, KNM-ER 739, KNM-ER 1504, KMN-KP 271 (Kanapoi), and Stw 431. Five extant hominoid populations are sampled to provide a standard by which to consider differences found between the fossils, including two modern human groups (Native American and African American), one group ofPan troglodytes, and two subspecies of Gorilla gorilla (G. g. beringei, G. g. gorilla). All possible painvise d values (average Euclidean distances) are calculated within each of the reference populations using an exact random- ization procedure. This is done using both raw linear measurements as well as scale-free shape data created as ratios of each measurement to the geomet- ric mean. Differences between each pair of fossil humeri are evaluated by comparing their d values to the distribution of d values found within each of the reference populations. Principal coordinate analysis and an unweighted pair group method with arithmetic averages (UPGMA) cluster analysis are utilized to further assess similarities and differences among the fossils. Fi- nally, canonical variates analysis and discriminant analysis are employed using all hominoid samples in order to control for correlations among variables and to identify those variables that discriminate among groups; possible affinities of individual fossils with specific extant species are also examined. The largest size differences, those between the small Hadar specimens and the two largest fossils (KNM-ER 739, IB 7594), can be accommodated easily within the ranges of variation of the two Gorilla samples, but are extreme relative to the other reference samples. The d values between most of the fossils based on shape data, with the notable exception of those associated