Craniomandibular integration patterns and evolutionary rates in cat-like carnivorans

The cat-like morphology is a textbook example of convergence, appearing in different vertebrate groups including two carnivorans families: felids and nimravids. Despite being grossly convergent, sabertoothed clades are now known to exhibit variable craniomandibular shapes. The gross shape and proportions of the craniomandibular complex of these groups have already been studied in detail; it is now time to untangle their disparity through the lenses of phenotypic integration and evolutionary rates. Indeed, the cranium and mandible have various purposes: from feeding to sensory functions. Those bones can be viewed as an arrangement of modules responding to different constraints that, if evolving independently, can lead to greater phenotypic diversity. We looked at the covariation between those two bones but also their different modules and computed specific rates of evolution using a database of 3D surface scans composed of 91 mandibles and 89 crania, spanning Oligocene to extant taxa. We quantified the shape using 3DGM with a total of 38 landmarks and semi landmarks on mandibles and 72 on crania. Our results show that the strength of integration is lowest in groups exhibiting longer upper canines; those same groups also show a burst of morphological evolution at the beginning of their evolutionary history. We therefore hypothesize that a low degree of integration coupled with rapid rates of evolution were two key components to develop a sabertoothed morphology