Widespread convergence towards functional optimisation in the lower jaws of crocodile-line archosaurs

Extant crocodilian jaws are subject to functional demands induced by
feeding and hydrodynamics. However, the morphological and ecological
diversity of extinct crocodile-line archosaurs is far greater than living
crocodilians, featuring repeated convergence towards disparate ecologies
including armoured herbivores, terrestrial macropredators, and fully
marine forms. Crocodile-line archosaurs therefore present a fascinating
case study for morphological and functional divergence and convergence
within a clade across a wide range of ecological scenarios. Here we build
performance landscapes of two-dimensional theoretical jaw shapes to
investigate the influence of strength, speed and hydrodynamics in the
morphological evolution of crocodile-line archosaur jaws, and test whether
ecologically convergent lineages evolved similarly optimal jaw function.
Most of the 243 sampled jaw morphologies occupy optimised regions of
theoretical morphospace for either rotational efficiency, resistance to
Von Mises stress, hydrodynamic efficiency or a trade-off between multiple
functions, though some seemingly viable shapes remain unrealised. Jaw
speed is optimised only in a narrow region of morphospace whereas many
shapes possess optimal jaw strength, which may act as a minimum boundary
rather than a strong driver for most taxa. Functional convergence is
common, with repeated evolution of shapes linked to specialised ecological
roles including gracile jawed piscivores and more robust jawed herbivores.