28 - Morphometric comparison of skulls of seals of the subgenus Pusa

Abstract

This chapter reevaluates the morphological relationships among the skulls of the three species of subgenus Pusa, namely, Phoca sibirica (Baikal seals), P. hispida (ringed seals), and P. caspica (Caspian seals), by sophisticated statistical methods, including multivariate statistics. The study finds that Baikal seals have larger relative growth coefficients for width of snout and nares. Larger zygomatic widths, greater length of jugal and smaller orbital width are evidence of the larger orbit of this species. Analyses of covariance reveal that Caspian seals have narrower skulls, brain cases, and bullae and ringed seals have a wider cranium, shorter snout, and larger bullae. The larger bullae of ringed seals suggest the importance of hearing ability in this species, which may be important for mothers to detect predators' approach in the lairs where they nurse the pups. Canonical discriminant analysis shows that interspecies differences are clearly greater than intraspecies differences in ringed seals. The phenograms indicates slightly closer morphological affinity between Baikal and ringed seals than between Baikal and Caspian seals. This finding lends support to the hypothesis that the Baikal seal is a descendant of an Arctic ancestor rather than a Paratethys relict.