Development and growth in skulls of three Otariidae species: a comparative morphometric study

Abstract

We examined the skulls ofArctocephalus australis,Callorhinus ursinusandOtaria byroniawith the objectives of (1) estimating the development and growth rates and comparing these parameters among the species; (2) describing the development for each linear measure, for each species and sex; (3) determining which variables are best correlated with age; (4) determining age of physical maturity. We employed traditional and geometric morphometric techniques to study the skulls. InA. australisandC. ursinus, skulls of females mature at about 6 years of age, and those of males at about 8 years.Otaria byroniamatures later, at about 9 years. Using geometric morphometric data sets, the rate and constant of growth inA. australisdid not differ between the sexes.Callorhinus ursinusandO. byroniashowed rates significantly different between sexes concerning growth (and in the constant as well), but onlyO. byroniadiffered between sexes in both developmental model parameters (rates and constant). Comparisons between the growth and developmental models showed significant differences in slope and constant. In both treatments employed, a relationship between size and shape dimorphism could be inferred for the skulls of all three species. We conclude that rates or timing of growth and development evolves within a conserved spatiotemporal organization of morphogenesis.