Roxy Perazzo
Research Mentor(s): Fabian Hardy
Mentor Department: Ecology and Evolutionary Biology
Authors: Roxy Perazzo, Rebecca Seay, Anne Kort, Fabian Hardy
Session: Session 4 (1:00pm – 1:50pm)
Presentation Type: Poster 54
Abstract
Tectonic processes shape landscapes, which drive faunal evolution. In particular, locomotor traits evolve in response to changing environments (Figueirido et al., 2015). Ecometric analysis studies connections between functional morphological traits and the environment, allowing the study of faunal responses to environmental change across taxa (Polly et al., 2011). Our research focuses on mammals in the Miocene Dove Spring Formation of southern California, which underwent several distinct tectonic episodes that reshaped the landscape between 12.5-8.5 Ma (Hardy & Badgley, 2023). The formation records an interval of vegetation change from closed-canopy forests to more open woodlands, but it is unclear whether the morphology of animals responded directly to this shift. Using a methodology developed by Andersson (2004), we examined elbow joint (distal humerus) morphology for 44 specimens across nine mammalian families as an indicator of cursoriality (adaptation for fast movement within open habitats) by landmarking six key points along the perimeter of the distal humerus. Previous work has shown that ambush predators display free supination (ability to rotate the humerus), while pursuit predators display restricted supination, indicated by a relatively flat or thick distal humerus, respectively. A shift towards open habitat would likely be associated with an increase in cursoriality at the community level and manifest as an overall shift towards restricted supination among families. We examined specimens within two time intervals (12.5-10.5 Ma; 10.4-8.5 Ma) to investigate changes in the average shape of distal humeri within the community over geologic time. By utilizing a principal components analysis (PCA) of landmarked data, we analyzed the major axes of shape variation in the humeri. We found that ungulates and carnivorans form distinctive groupings, though canids lie closer to ungulates than other carnivorans. Multivariate regression analysis confirmed a statistically significant correlation between distal humerus shape and size. A MANOVA test revealed statistically significant differences in shape across orders. The humeri of artiodactyls are generally flat and rectangle-shaped, facilitating higher cursoriality than the angular condyles observed in carnivorans. Our next steps will be to compare our humerus shape data to those of modern mammals with known locomotor modes and thus determine if the changes in our dataset match the shape of modern, cursorial mammals. Our findings will help to develop our understanding of the links between ecosystem and faunal change, with implications for processes affecting modern mammalian habitats.
