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Morphologic distinctions and particularities of pygmy blue whale body proportions
Sazhinov EG (translation by Trevor A. Branch and Yulia Ivashchenko)
International Whaling Commission
Thus, despite the small amount of material, it is possible to establish some of the features of the formation of the proportions of pygmy blue whale body shape in the embryonic state and subsequent changes in postnatal individuals. Head sizes are relatively larger (and have higher growth rates), as a fraction of total length, in the embryonic and post-embryonic periods. The relative sizes of the tail of the body in embryos are greater than in adults. The relatively shorter length of the tail as a stable sign of adult animals is established when they reach a length of 20 m in males and 21 m in females. The relative sizes of the pectoral fins (length and width) in newborns are greater than in adults. After birth as a whale grows and develops their relative sizes get smaller. Our analysis of the proportions of the common blue whale in the Antarctic and the pygmy blue whale once again confirms the existence of differences in the external morphological characters of both species and the validity of distinguishing the pygmy blue whale in as a separate subspecies or even species. The formation of blue pygmy whales as an independent taxonomic unit probably occurred in the relatively recent phylogenetic period, which is confirmed by the appearance of stable morphological differences only in the late stages of embryonic development.