Anatomical networks reveals new adaptive strategies of cetacean flippers

Abstract

Previous studies of the anatomical network analyses (AnNA) of pectoral fins of tetrapods that have been secondarily adapted to the marine environment identified two main strategies: most limbs have superficial and interdigital connective tissue which gives to the limb the shape of a "baby mitten" (observed in marine mammals and most reptiles), whereas ichthyosaurs are characterized by a homogeneous reintegration of the limb. That initial sample included only two extant cetaceans, which did not show a clear tendency to follow any of the defined adaptation paths. Cetacean flippers evolved from the forelimbs of a group of terrestrial artiodactyls. The transition to the aquatic environment entailed multiple morphological changes in the bone anatomy and the limb´s soft tissues. As a consequence of these transformations, there is interspecific variation (e.g., the number of phalanges and carpals and their connections). In order to know the adaptive tendencies of the flippers in extant cetaceans and the group´s morphological diversity, an AnNA was carried out with a larger sample.