Search for: All records

Significance Understanding how development and evolution shape functional morphology is a basic question in biology. A paradigm of this is the finch’s beak that has adapted to different diets and behaviors over millions of years. We take a mathematical and physical perspective to quantify the nature of beak shape variations, how they emerge from changes to the development program of the birds, and their functional significance as a mechanical tool. 

Abstract The dorsoventrally flattened skull typifies extant Crocodylia perhaps more than any other anatomical feature and is generally considered an adaptation for semi‐aquatic feeding. Although the evolutionary origins of caniofacial flattening have been extensively studied, the developmental origins have yet to be explored. To understand how the skull table and platyrostral snout develop, we quantified embryonic development and post‐hatching growth (ontogeny) of the crocodylian skull in lateral view using geometric morphometrics. Our dataset (n = 103) includes all but one extant genus and all of the major ecomorphs, including the extremely slender‐snoutedGavialisandTomistoma. Our analysis reveals that the embryonic development of the flattened skull is remarkably similar across ecomorphs, including the presence of a conserved initial embryonic skull shape, similar to prior analysis of dorsal snout shape. Although differences during posthatching ontogeny are recovered among ecomorphs, embryonic patterns are not distinct, revealing an important shift in developmental rate near hatching. In particular, the flattened skull table is achieved by the end of embryonic development with no changes after hatching. Further, the rotation of skull roof and facial bones during development is critical for the stereotypical flatness of the crocodylian skull. Our results suggest selection on hatchling performance and constraints on embryonic skull shape may have been important in this pattern of developmental conservation. The appearance of aspects of cranial flatness among Jurassic stem crocodylians suggests key aspects of these cranial developmental patterns may have been conserved for over 200 million years.