Convergent traits in mammals associated with divergent behaviors: the case of the continuous dental replacement in rock-wallabies and african mole-rats

The study of convergences in mammals is crucial to understand the evolutionary processes underlying the origin of shared traits. A classic example is the independent evolution in the pygmy rock-wallaby, the silvery mole-rat, and manatees of continuous dental replacement to compensate for high dental wear. The origins of continuous dental replacement in mammals remain unresolved. As the functional study of a trait may permit pinpointing the adaptive nature of its independent evolution, we aimed at comparing first the morpho-functional characteristics of the masticatory apparatus between the pygmy rock-wallaby and their closest relatives, and then with some published data on the silvery mole-rat. 3D geometric morphometric and biomechanical analyses were complemented by dental microwear analyses. Our results showed that the pygmy rock-wallaby clearly departs from its relatives in having a wider skull, a shorter snout, and a dentition situated more distally. These cranial modifications, previously observed in the silvery mole-rat, are probably linked with a neotenic development. Because of higher developmental constraints on marsupial skulls, such adjustment in the pygmy rock-wallaby may have improved the force generated by adductor muscles at molars for comminution of tough and abrasive plants. In contrast, the strong attrition combined with the ingestion of dust during high activity of digging and feeding might contribute to both molar damage and high wear in the silvery mole-rat. Our results stress the importance of combining morphological, developmental, and functional data to show that different behaviors related to ecology can explain the convergent occurrence of continuous dental replacement in mammals.