Morphological evolution of carnivoran milk teeth
DANA REUTER
Junior Geology major at Mount Holyoke College
REU Mentors: Dr. Kenneth Angielczyk (Curator, Geology) and Dr. Susumu Tomiya (Postdoctoral Researcher, Geology)
Symposium Presentation Title: Morphological evolution of carnivoran milk teeth
Symposium Presentation Abstract: Carnivoran tooth morphology has been well documented over the years to gain insight into their ecology and phylogeny. Despite this knowledge, there has been very few efforts to study their deciduous tooth morphology. In this study we investigated the evolution of carnivoran milk teeth in a phylogenetic comparative framework, focusing on how their shapes are related to those of adult teeth. We measured milk and adult teeth of 33 species from the families Canidae, Ursidae, Mustelidae, Felidae, Hyaenidae, Herpestidae, Nandiniidae, Viverridae, and Procyonidae. We used the phylogeny and measurements to see general trends in the morphology of both the milk teeth and their adult counterparts. We conducted: (1) principal component analysis to identify major variations among species in relative shear length, carnassial shape, and pre-carnassial shape and size, metrics that are closely tied to diet differences in adults; (2) phylogenetic regression analysis to the strength of correlation between milk and adult tooth shapes. We found that, although milk teeth are very similar to adult teeth in their morphology, there are some differences within some dentally specialized groups; for example, felids and hyaenids have proportionally more grinding area in their milk teeth and bears have relatively small milk teeth compared to their adult counterparts. Canids are conservative in their morphology compared with other taxa. Carnassial shape is significantly more variable in adults than in juveniles (Fligner-Killeen test, P = 0.004) because the evolutionary rate is higher in adult carnassial shape (s2 = 3.8 x 10-3) than in milk carnassial shape (s2 = 1.4 x 10-3). These findings suggest that milk tooth morphology harbors potentially valuable information for phylogenetic reconstruction. The more limited variation in the shape of deciduous carnassial tooth may reflect evolutionary constraint or a more homogeneous selective pressure on juveniles across specie. Testing these hypotheses will require further research incorporating extinct groups and information on juvenile diets and weaning ages.
Original Project Title: Morphological evolution of carnivoran milk teeth
Original Project Description: Carnivorans (dogs, cats, and their relatives) show remarkable diversity of forms and habits. The variations in the shapes of their cheek teeth are prime examples of dietary adaptations that enabled different lineages to exploit such disparate food items as fruits, insects, mollusks, and vertebrate meat. However, most of what we know about the relationship between diet and tooth shapes in carnivorans is based on studies of adult teeth. Do the milk teeth of carnivorans show a range of dental morphology comparable to that of adult teeth? The goal of this project is to investigate whether similar selective pressures drive the morphological evolution of milk teeth and adult teeth.
Research methods and techniques: We will examine carnivoran skulls in the Mammals Collections of the Field Museum to gather information on the shapes of milk teeth, taking detailed notes and photographs. Measurements of the milk teeth will be taken that, when taken from their adult counterparts, are known to be indicative of adult diet. Variation in the shapes of milk teeth among species will be described. Using phylogenetic comparative methods, we will test how closely milk-tooth shapes are: (1) correlated with adult-tooth shapes; and (2) tied to juvenile/adult diet.
