109-1 Dental Row Measurements and Horncores Reveal Interspecific and Intraspecific Variation of the Merycodonts (Mammalia: Artiodactyla: Antilocapridae: Merycodontinae) with Implications for Merycodont Systematics

Session: Working Up an Apatite: Teeth as Paleo -Ecological and -Climatological Archives (Posters)

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Abstract:

Merycodonts represent a paraphyletic subfamily of antilocaprids that were present throughout North America during the early to middle Miocene and included five genera (Cosoryx, Merriamoceros, Merycodus, Paracosoryx, and Ramoceros) with nearly two dozen species described between them. A characteristic feature of antilocaprids is the occurrence of prominent horns, preserved as bony horncores in fossil species. However, like with many fossil vertebrates, teeth and jaws are among the most commonly preserved elements. Previously, merycodont taxonomy had a large emphasis placed on differences between horn morphologies to diagnose species but it has long been recognized that standard measurements of dentition (such as premolar row vs molar row length) are less variable and more biologically informative of differences between species than widely variable characters like horns. Here we examined the degree of dental row variation and horncore morphological variation of merycodonts, by comparing their range of variation within the modern antilocaprid, Antilocapra americana, to the that of merycodont species. We used a large sample size of horncores and jaws from the AMNH and a single population known from the Siebert Fm. in Tonopah, Nevada housed at the LACM for qualitative examination of interspecific and intraspecific variation of horncores in the context of less variable, quantitative traits like tooth row measurements. Our multivariate analysis of variance (MANOVA) and post-hoc (Tukey) results emphasize the importance of utilizing more static characters, like those in tooth rows, for support in systematic decisions. Further, we illustrate that horn morphology is variable among modern populations of Antilocapra americana and supports the idea that it is dubious to put too much taxonomic weight on horncore morphology alone to diagnose a species. We also calculated the Coefficient of Variation (CV) between Antilocapra and the five merycodont genera from dental rows, which revealed that molar and premolar length dimensions, for Antilocapra and for each of the merycodont genera are similar, suggesting a similar degree of species variability may be expected for merycodonts. Ultimately, this research presents the wide range of horncore variation and statistically significant degree of dental measurement overlap among many merycodont species. We discuss the implications of these findings for future revised merycodont systematics.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9614

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