Evolutionary transformations of the malleus in pinnipeds, with emphasis on Southern Hemisphere taxa

Abstract

The systematic value of the middle-ear ossicles, in particular the malleus, has been long recognized for diverse groups. We present systematic work on the characters of the middle-ear ossicles of pinnipeds, focusing on until now poorly studied Southern Hemisphere species. Mallei were extracted from 16 specimens of pinnipeds belonging to five austral and one boreal species of Phocidae and two austral species of Otariidae. Several characters used in this study have been described previously, and some were here modified. Three new characters are here defined and analysed. All characters were mapped onto the phylogeny. Our character analysis shows the transformations that have occurred in the evolution of middle ear ossicles in pinnipeds and identifies diagnostic features of many of its clades. Beyond the identification of specific changes within eachclade, our study of pinniped ossicle evolution documents the occurrence of anatomical convergences with other groups of mammals that live in an aquatic environment, as has occurred in other organ systems as well.