Allen, B.M., R.E. Chapman, J. G., Mead. Species and Sex Determinations of Mesoplodon and Ziphius Based on Mandibular Measurements.

Identifications of beaked whale species from skeletal material are difficult, particularly from incomplete specimens. Most diagnostic characters are found in the skulls, mandibles, and teeth; however, interspecific variations have only been generally or subjectively categorized. In order to compare differences between and within a species, both ontogenetic and sexually dimorphic characters need to be better understood.

Sexual dimorphism is known to occur within beaked whales to varying degrees and is often solely used to determine gender, although these differences have only been crudely quantified within each species. We examined mandibles of two genera of beaked whales, Mesoplodon and Ziphius, to test whether mandibular measurements can be used to make taxonomic identifications and sex determinations.

Gender was included in the dataset only if reproductive organs were examined by the collector. Three-dimensional coordinate data were obtained for ten homologous landmarks on each specimen using a Microscribe 3-DLX digitizer. These coordinates were used to calculate the distances between landmarks, and the resulting 45 measurements were compared using multivariate statistical analyses.

Results suggest that measurements based on alveolar position, alveolar length, and symphyseal length were most informative for determining species and sex of an individual. Such information provides insight into which mandibular measurements are most informative for ascertaining species identifications of beaked whales. Mandibular measurements may consequently be useful for making accurate species identifications of stranded or incidentally taken beaked whales, especially if used in combination with other identification techniques.

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