Shape analysis of odontocete mandibles: functional and evolutionary implications

• Other Authors: Barroso, Celia (author), Biology (department), Berta, Annalisa, Burns, Kevin, Bailey, Barbara, Cranford, Ted
• Format: Thesis
• Language: English
• Published: 2010
• Subjects: QH302.2; toothed whales
• Online Access: https://hdl.handle.net/20.500.11929/sdsu:4826

Odontocete mandibles serve multiple functions, including feeding and hearing. One hypothesis is that sound enters the hearing apparatus via the pan bone of the posterior mandibles (Norris, 1968). Another viewpoint, based on computer models, suggests that sound enters primarily through the gular apparatus and the opening created by the absent medial wall of the posterior mandibles. The posterior region of each mandibular ramus has a large, hollow cavity called the mandibular foramen that contains a bulging mandibular fat body (MFB), which terminates on the bony tympanoperiotic complex. The acoustic properties of these fat bodies suggest that they refract sound. This unambiguous link between form and function has catalyzed this current study of mandibular shape. Previous studies have described odontocete mandibles using linear morphometrics and focused on multiple populations within single genera. Geometric Morphometrics (GM) is used to avoid some limitations of linear morphometric studies, using relative 3-D landmark positions instead of lengths. This technique measures shape only, excluding any scaling, rotational, and positional effects. The primary objective of this study is to use GM to quantify mandibular shape across all major lineages of Odontoceti. Eighty-five mandibles, comprised of 40 species, representing all major lineages were included in the shape analysis. Twelve landmarks found on each mandible represent regions of the symphysis and mandibular foramen. The majority of shape variation was found in Jaw Flare and Symphysis Elongation (85.5%). Shape differences in the mandibular foramen also accounts for a portion the total variation (10.9%). The mandibles are an integral component of the sound reception apparatus in toothed whales and the geometry of the mandibular foramen likely plays a role in hearing. The second objective of this study is to assess correlates of hearing and mandibular foramen geometry derived from the GM shape analysis, as well as from linear morphometrics. Echolocation peak ...