MCKENNA, M. F.; CRANFORD, T.W.; BERTA, A.; San Diego State University; San Diego State University; San Diego State University: Defining the odontocete melon: Comparisons using Morphometric Analysis

The term �melon� refers to unique lipid soft-tissue structure in all toothed whale foreheads. A large body of evidence suggests that the melon is functionally important in bio-sonar development and evolution in odontocetes. However, it is difficult to maintain the geometry and spatial relationships between soft tissue structures in dissection-based studies of gross anatomy; therefore, prior characterizations of the melon have lead to ambiguous functional and phylogenetic interpretations. This study presents an innovative approach, geometric morphometrics, to define the melon though shape analysis of the bony and soft tissue structures of the forehead. Profiles were selected from a mid-sagittal plane in CT scans of 25 postmortem odontocetes representing six extant families (Delphinidae, Phocoenidae, Ziphiidae, Kogiidae, Pontoporiidae, and Physeteridae). A Procrustes analysis of selected homologous landmarks and semi-landmarks permits statistical comparison of the shape distances. We found a significant difference between odontocete families in various tissue regions. Warp analysis shows that most of the changes occur in the region of the nasal bones, which is consistent with previous anatomical descriptions. The methods presented here will be expanded, and comparisons made among extant and extinct odontocetes.