The contribution of ontogenetic growth trajectories on the divergent evolution of the crocodylian skull table.

Abstract

To explore shape variability among crocodylian skull tables, an analysis using geometric morphometric methods is conducted with the inclusion of extant and fossil taxa. Skull tables are variable and the differences likely play a role in hydrodynamics, species recognition, and biomechanical adaptations. Comparisons of allometric change within taxa are explored revealing that adults significantly diverge from juvenile skull table morphologies in most species and these changes happen in a stereotyped way. In all analyses, adults of the smallest extant taxa plot alongside the juveniles of related taxa and heterochrony may explain the maintenance of these morphologies into adulthood. When landmarks representing the supratemporal fenestrae are included, longirostrine taxa are broadly separated from one another due to variation in the size of the supratemporal fenestrae. The hypotheses of previous studies suggesting that the size of the supratemporal fenestrae is influenced by snout length-with longer snouts corresponding to larger fenestrae-must be re-evaluated. Although species of the crocodyloids Tomistoma and Euthecodon approach or exceed the length of the snout in gavialoids, their supratemporal fenestrae are proportionally smaller-this suggests a phylogenetic constraint in crocodyloids regardless of snout length.