Morphometric analysis of embryonic development in Alligator mississippiensis, Crocodylus johnstoni and Crocodylus porosus

The size of embryos at various stages of development was determined in three species of crocodilian ( Alligator mississippiensis, Crocodylus johnstoni and C. porosus). Various morphometric measurements were taken of embryos throughout development and were described for each stage of development. Increase in size from stage to stage was faster in A. mississippiensis than in C. porosus and C. johnstoni. Hatchlings of A. mississippiensis were large in length but light in mass compared with the hatchlings of C. johnstoni and C. porosus which were heavier per unit length. These morphometric parameters can be used to determine the stage of embryonic development by size. The use of principle component analysis improves this technique further by dampening any anomalous data points.
The rate of embryonic growth in A. mississippiensis appeared to be under greater genetic control than in the two species of Crocodylus. The evolutionary advantages of this phenomenon probably relate to the biology of A. mississippiensis. Due to the northerly range of this species it is advantageous for alligators to hatch as soon as possible, as large as possible, to maximize the period prior to winter hibernation and reduce predation. Tropical crocodiles have fewer selection pressures for rapid development and have slower rates of embryonic growth. Genetic aspects of crocodilian embryonic development have been largely ignored but may help explain some aspects of crocodilian growth under farming conditions.