Tooth Crown Shape Variation in Homo erectus: A Test of Species Homogeneity Using Bootstrapping
, , and (University of Nevada, Las Vegas)
Are there multiple species within the H. erectus hypodigm? Some researchers support the presence of two distinct, yet phylogenetically related, species within H. erectus sensu lato: H. ergaster and H. erectus, whereas others propose only a single species exhibiting an extremely large geographical and temporal distribution. While previous taxonomic analyses of H. erectus have focused on variability in size among fossils, researchers have noted the greater importance of shape variables when testing for species distinctions. Consequently, this study uses geometric morphometric techniques to analyze shape separately from size variation in mandibular first molars commonly attributed to H. erectus (n=9), H. ergaster (n=9), and H. sapiens (n=25). Twenty-five Landmarks were collected for each specimen using tpsDig2 data acquisition software to interpret overall crown shape and cusp apices.
The paucity of preserved fossil remains presents a significant obstacle in studying the fossil record. To address this, resampling and bootstrapping techniques were to increase fossil and modern human sample sizes. This method effectively increases the amount shape data and produces conservative estimates of taxonomically diagnostic differences in fossil hominids.
Multivariate analyses were used to determine the presence of multiple species in H. erectus s. l. In a canonical variates analysis (CVA), confidence intervals for the fossil samples exhibited some overlap, suggesting morphological similarity between groups. Additional multivariate tests of shape support results of the CVA. As a result, it is proposed that shape variation in mandibular first molar crowns is not great enough to suggest the presence of multiple species within the hypodigm.