Meeting Abstract
In contrast to the high degree of complexity exhibited in most terrestrial mammals teeth, marine mammals have undergone a simplification. Most toothed whales and pinnipeds have simple conical teeth suitable for grasping and holding prey. Yet how the number and placement of these teeth evolved and varies in many species is problematic. From the early 1900’s, a variety of studies ranging from the subspecies- to subpopulation-level of walrus have attempted to discern a dental formula for juvenile and adult members of Odobenus rosmarus. While varying conclusions were reached, each study notes between 10-25% of individuals that do not conform to observed patterns for number or placement of teeth. Determining the homology of teeth in Odobenidae is complicated by several factors. Previous work on fetal to juvenile individuals records some individuals with three sets of teeth over life history (milk, deciduous, adult) while others are born toothless and only develop the later two sets. Furthermore, juvenile dentition is observed forming both in alveolar and gingival settings, with some alveolar teeth forming in sockets later containing adult teeth while others are reabsorbed. We suggest, rather than a standard number of teeth present in a breeding age individual, there is a standard total occlusal area (TOA) relative to skull proportions of each individual. To measure occlusal area skulls and mandibles are photographed and measured using ImageJ. Preliminary data suggests that TOA of upper teeth normalized against palate length, and total TOA of lower teeth normalized to the length of the right mandible, is more consistent across the species than tooth number. Furthermore, males thus far have a lower number of individuals deviating from previously published standard dentition than females.
