Meeting Abstract

P1.202  Saturday, Jan. 4 15:30  Blue Whale (Balaenoptera musculus) Anatomy at the Transition between the Embryonic and Fetal Periods ROSTON, RA; Duke University rachel.roston@duke.edu

The morphological transformations associated with the secondary adaptation of cetaceans to aquatic life are well-documented in the fossil record. The ontogenies of extant cetaceans may clarify developmental origins of these macroevolutionary changes. Stages of odontocete (toothed whale) embryology have been defined, but the applicability of these stages to mysticete (baleen whale) development is largely unknown. In this study, the external and internal anatomy of a 130-mm blue whale fetus (Balaenoptera musculus), the largest mysticete, is described using microCT. Externally, the specimen resembles a late-stage odontocete embryo due to the lack of a fluke and dorsal fin, but resembles an early-stage odontocete fetus due to its elongated rostrum. Internally, the dermal cranial bones are partially ossified and do not yet overlap posteriorly as in an adult, much like odontocetes of a similar developmental stage, and the endochondral skeleton is cartilaginous. Within the larynx, the U-fold and laryngeal sac are approximately parallel to the body axis and airflow, much as in a balaenopterid adult. The gestational age is estimated to be 65 days by combining fetal morphological data with fetal length data from the International Whaling Statistics, historical accounts of blue whale migratory and reproductive habits, and published descriptions of fetuses of congeneric species. These data show that some but not all major balaenopterid characteristics are present before the onset of rapid growth during the fetal period.