Extending the utility of artiodactyl postcrania for species-level identifications using multivariate morphometric analyses

Abstract

Michel. 2012. Extending the utility of artiodactyl postcrania for species-level identifications using multivariate morphometric analyses. Palaeontologia Electronica Vol. 15, Issue 1; 1A:22p; palaeo-electronica.org/content/2012-issue-1-articles/68-artiodactyl-postcrania ABSTRACT Studies of paleoecology are most powerful when relative abundance data are available at fine taxonomic scales and large sample sizes. Postcranial elements are abundant but seldom identified to species, reducing potential sample size. We investigate whether antilocaprid astragali, abundant in the Late Miocene deposits of the Great Basin, can be identified to species, improving sample sizes. Our analysis of African and Asian bovid data from the literature suggests species should be distinguishable using astragalar dimensions. For our case study we use three species of antilocaprids, Ilingoceros alexandrae, Ilingoceros schizoceras, and Sphenophalos nevadanus from the Hemphillian (~8 Ma) Thousand Creek Fauna of northwestern Nevada. These species are diagnosed by their horncores, but previous comparisons of their dentition have shown no clear separation between the species. Our analysis of >200 antilocaprid astragali from Thousand Creek indicates there is enough variation to tentatively reject the hypothesis of only one species, but the distribution does not allow assignment of individual astragali to species. Combined with horncore morphology, our results suggest differences in male-male competition and a slight difference in body size kept the two genera out of competition while ecological similarity and/or shared ancestry created a continuous distribution of astragalar dimensions. The data cannot resolve whether I. alexandrae and I. schizoceras are distinct species. Additionally, we explored the range of effectiveness of a published discriminant function developed to derive environmental preference from African bovid astragali. Applying this discriminant function to Antilocapra proved ineffective, likely a consequence of the distinct evolutionary histories of antilocaprids and bovids.

Geometric morphometric analyses of worn cheek teeth help identify extant and extinct gophers (Rodentia, Geomyidae)

“…Feranec et al . ; McGuire ; Calede & Hopkins ; Davis & Calede ; Davis & McHorse ). This work has often focused on teeth because of their utility in mammalian taxonomy and abundance in the fossil record (see Smith & Wilson ) but it can be complicated by the change in apparent tooth shape with wear in hypsodont taxa (e.g.…”

Astragalar Morphology of Selected Giraffidae

“…Conversely, Prodremotherium is the smallest of all the taxa evaluated, and this species has a notably long astragalus. It has been previously demonstrated that that bovid astragali dimensions positively correlated with body size [6]. It is also possible that there was a convergence in the astragalar shape of Bohlinia and Honanotherium with that of Sivatherium and Helladotherium , likely relating to locomotory differences.…”

“…The functional morphology therefore likely represents a mosaic of features shaped both by the phylogenetic history and environment of a species. DeGusta and Vrba (2003) and Davis and Calède (2012) apply strictly metric values to predict environmental preferences and to test species differences [5,6]. Our morphological features analyze astragalar characteristics of discrete aspects of the bone, which are not detected in broader metric comparisons.…”

“…Astragalar features have been used to define Proboscidea, Archonta, and Artiodactyla [2–4]. Morphometric analyses of mammalian astragali, however, have been largely unsuccessful in separating species, but have greater utility in paleohabitat predictions [5,6]. Morphometric features of the astragalus can provide information on body size, as well as ecological habitat [7].…”

A method for improved identification of postcrania from mammalian fossil assemblages: multivariate discriminant function analysis of camelid astragali

“…The Martinez and Sudre (1995) examination of Paleocene artiodactyl astragali demonstrated conclusively that astragalar size is tied directly to body size, leading to the identification of two separate species at one site based on mass estimates. Davis and Calède (2012) demonstrated additionally that the DeGusta and Vrba (2003) astragalus dataset contains enough taxonomic information to potentially diagnose genera of African antelope. Consequently, multivariate analysis of camel astragali should reveal body-size partitioning in the Thousand Creek taxa if it exists, as it does among many modern coexisting artiodactyls (McNaughton and Geor giadis, 1986), and may provide enough information for generic diagnosis.…”