Meeting Abstract
Some analyses of pathologies in the fossil record use these pathologies to infer specific behaviours or ecologies for extinct animals. This is problematic because different types of injuries and diseases can result in similar gross pathology. Instead, here we conducted a synthesis of the phylogenetic distribution of evidence for bone healing and regeneration in vertebrates (especially tetrapods) to reconstruct how these traits evolved. Where feasible, we also used µCT scanning to determine whether an unusual bony feature was pathological. This was especially relevant for animals with a fragmentary fossil record, because a lack of comparative specimens or small sample size makes it difficult to distinguish between normal osteological traits and pathological growths. We report new cases of pathological bone formation in the limb bones of two early tetrapods, Crassigyrinus scoticus and Eoherpeton watsoni, from the Carboniferous of Scotland. These features were initially interpreted as unique sites of muscle attachment, but our scans revealed the pathological nature of the trabecular and cortical bone arrangement. Comparison of the pathology in the aquatic Crassigyrinus with the previously reported pathology in the Carboniferous tetrapod Ossinodus pueri reveals that we cannot infer terrestrial behaviour from such pathologies. However, these pathologies nonetheless have a broader importance. Although different bone healing pathways exist in extant taxa (distinguished by the presence or absence of cell dedifferentiation), our preliminary analysis including evidence from the fossil record suggests that vertebrates evolved the ability to repair bone in response to injury early on, perhaps as an exaptation of the bone modelling abilities involved in normal bone growth.
