Evolution of modularity and morphological integration in skulls of Odontoceti (Mammalia, Cetacea) as full-time swimmers and sound-dependent mammals

Abstract

Cetaceans are aquatic mammals of order Artiodactyla, whose earliest fossil is a terrestrial mammal from the early Eocene (~ 54 Mya). This clade comprises stem cetaceans (or 'archaeocetes'), as well as the extant taxa in the suborders Odontoceti (c. 78 species) and Mysticeti (c. 15 species). Cetaceans present profound cranial changes related to the 'telescoped' skull, remarkable directional asymmetry - only in recent odontocetes, and feeding specializations. These skull shape variations have been associated with adaptations in feeding anatomy e.g. feeding apparatus and sound production to explore specific ecological niches. Current knowledge about odontocetes suggests the presence of cranial modules associated with habitat use (e.g. coastal or oceanic waters), prey preferences (e.g. fish or cephalopods), and sound production for environmental exploration (i.e. echolocation). Even so, the diversity of cranial modules and their integration remain unanswered, with emphasis on the changes that occurred throughout the phylogeny, as proposed here. Based on the knowledge that mammalian skulls have distinct functional modules, and differences in the levels of interaction between them, this proposal aims to identify the morphological modules in skull of odontocetes. In addition to investigating the patterns and magnitude of integration of these modules associated with the development, function and evolution of this taxon. The sample comprises H2,600 skulls belonging to c. 78 species of odontocetes held in 40 collections. Linear measurements resulting from the conversion of 3D coordinates obtained by geometric morphometrics will be used in analyzes related to shape and statistical modelling to verify the association between shape and evolutionary drivers related to interaction with environments.