Meeting Abstract

27.5  Jan. 5  Cranial ossification and growth patterns of balaenopteroid mysticetes WALSH, B.M.*; BERTA, A.B.; San Diego State University; San Diego State University bredamckay@yahoo.com

The sequence of ossification of sutures in the skull of baleen whales (mysticetes) can be used to characterize the relative age of these animals. We examined occipital suture closure in four neonate mysticete species and determined that gray whale calves have open occipital sutures until approximately 6 mos. of age and are born at a more developmentally juvenilized stage than closely related fin, minke and humpback whales. In examination of the cranial growth over the life span of these species, we computed allometric cranial growth patterns of the different ontogenetic stages (calf, juvenile, mature) with log linear regression analysis of eight cranial measurements. Previous studies found that juvenile mysticetes grow slower than calves attributed to their adjustment to different nutritional supplies, but differences in cranial growth patterns has not been described. This study uses a larger data set than previously available for comparison and description of cranial growth and classification of ontogenetic stages among a group of closely related balaenopteroid mysticetes (Balaenopteridae + Eschrichtiidae). The results of this investigation suggest that the dimensions of the skull grow at different rates depending on ontogenetic stage and species. This analysis indicates that the skulls of balaenopteroids develop at a rapid rate during the first year, along with total body length; however, each species has its own cranial growth pattern that cannot be generalized for all mysticetes, as has been done in previous studies.