Morphometric Analysis of an Ontogenetic Series of Dolphin Cranial Endocasts

The earliest stages of life mark a critical period of brain growth and cranial expansion that has been thoroughly studied in many cognitively complex species but not in dolphins. Marine mammal protection policies restrict certain invasive avenues of research critical to understanding brain growth in other species, but previous studies have found success in using CT scans from deceased, stranded dolphins to understand brain morphology through endocranial data. Thus, this study aimed to utilize cranial endocasts as a proxy for brains. Using the 3D surface modeling program Avizo, I generated virtual cranial endocasts from CT scans of an ontogenetic series of dolphin skulls. The endocasts were then 3D printed and used to form a silicone mold in which the cerebrum and cerebellum were individually delineated, modeled with clay, and weighed. Specimen ages ranged from fetus to adult. Existing literature has shown that before birth, the growth of the dolphin cerebellum surpasses that of the cerebrum; it has been suggested that this is due to establishing basic motor functions controlled by the cerebellum in preparation for aquatic life. Thus, I predicted that after birth the growth rate of the cerebrum will be faster than that of the cerebellum as more cognitively complex behaviors such as social interaction develop. However, hindbrain data collected through these methods were imprecise and could not be used. Future research might have more success with different, more sturdy types of molds and mold-making materials. This method may best be applied to older specimens with more developed cerebella.