IDENTIFICATION OF MAMMALIAN POSTCRANIA USING MULTIVARIATE ANALYSIS: CLASSIFYING ASTRAGALI OF CAMELIDAE (MAMMALIA) FROM THE LATE MIOCENE OF NEVADA

Fossil camelids are an important part of the Miocene mammal faunas of western North America. As with most fossil mammals, diagnoses of camelid taxa are made almost exclusively through cranial and dental characters. Unfortunately, taphonomic processes leave many Miocene mammalian localities with few, if any, cranial elements and a plethora of postcrania, confounding accurate estimates of diversity. Simple, accurate methods for identifying mammalian taxa from postcranial remains are necessary to recover correct estimates of both taxonomic richness and evenness.

Much previous work on postcranial identification of camelids has focused on qualitative characters. Here I employ a quantitative method, using multivariate methods recently proposed for African antelope, to classify astragali from the Hemphillian Thousand Creek Fm. of northwestern Nevada. To provide a reference dataset, 1398 measurements were made on 204 astragali representing the genera Aepycamelus, Megatylopus, Procamelus, Alforjas, and Hemiauchenia from several Hemphillian localities where the identification of camelids could be made from their teeth. Astragali were chosen because, as durable skeletal elements, they are commonly preserved intact and are abundant in many Miocene terrestrial mammal deposits. The five genera included in this analysis are easily distinguished by the first principal component, but show no distinction on the second or third components, indicating that astragalar shape is conserved within the Camelidae and these taxa are only distinct in size. Using these results to identify Thousand Creek camels, four genera are present: Aepycamelus, Megatylopus, Procamelus, and Hemiauchenia, listed here in increasing relative abundance.

The presence of four genera of camels at one locality is apparently rare. Several other well-sampled Miocene localities in North America have a similar diversity of camels, but two or three genera is a more common diversity. The paucity of cranial or dental material at Thousand Creek makes this result difficult to test with standard taxonomic methods. Future investigation of other postcrainial elements, including calcanea and metapodials, will be used to test these results before applying them to other localities.