Testing dental calculus as a means to determine paleodiet of extinct equid Merychippus sp.

Abstract

During the Miocene Epoch, radiation of merychippine equids may have coincided with a transitional North American habitat of forests with patches of open grassland, and merychippine diet may reflect this diverse environment. Dental calculus on teeth of extinct herbivores like Merychippus can incorporate a long-term dietary record in the form of plant microfossils, such as phytoliths and fibers. In the present study, the purpose was to test dental calculus as a measure of paleodiet in equids by identifying and comparing Merychippus paleodiet constituents among preliminary sample groups. Calculus samples obtained from seven isolated Barstovian age Merychippus teeth from sites in Nebraska, Oregon, and Maryland, USA contained plant microfossils that were identified to categories based upon morphological characteristics. Grass silica short-cell phytoliths of BOP clade, C 3 -pathway subfamilies were most frequent, comprising 45–57% of all calculus samples. Microfossils from woody taxa were also present in all assemblages (18–29%). Softwood tracheary elements and sedge grass phytoliths (Family Cyperaceae) were significantly more frequent in Merychippus from the Maryland site. The combined presence of hardwood and grass microfossils from each Merychippus specimen indicates a mixed browse/grass diet that included C 3 grasses, supporting recent micro- and mesowear analyses. Some significant differences among these preliminary samples suggest that calculus is a valid means to compare diet among regions. Within a broader context, this type of study can generalize aspects of the Merychippus paleoenvironment and stands as an evaluation for using microfossils from dental calculus as a means for diet determination. • Microfossils from calculus on 7 Merychippus teeth are used to find evidence of diet. • Presence of pooid grass phytoliths indicates C 3 grasses in the environment. • Presence of hardwood microfossils suggests browse in diet. • Tracheid microfossils indicate possible dietary inclusion of softwood species. • Microfossils in Merychippus calculus are consistent with previous findings.