Meeting Abstract
Morphometric analysis seeks to describe variation in form among taxa in an evolutionary or functional context. Although both traditional (linear) and new (geometric) techniques have been used, limitations and advantages exist for each with respect to ease of data acquisition and analysis. Little is known about the ontogenetic morphometrics of vertebrate heads, including a single published study of crocodile postnatal head development. Thus, the purpose of this study was characterize ontogenetic changes in the alligator cranium throughout embryonic development. We recorded and analyzed six linear cranial measurements in 77 preserved embryonic American alligators representing 20 different stages. Examination of the individual measurements revealed dynamic inter-relationships among the measured dimensions during development. Using both principal components analysis (PCA) and estimates of cranial component volumes, we found three distinct phases in embryonic alligator head growth. We identified a critical second phase which disrupts an otherwise monotonic developmental trajectory characterized by a period of reduced snout growth with respect to cranial growth. A similar growth pattern, without the intervening second phase, has been observed in prenatal humans, and the reversed pattern was observed between postnatal humans and crocodiles. The exact nature of the pre- and postnatal developmental allometries requires further elucidation.
