Tooth and long bone scaling in Sardinian ochotonids (Early Pleistocene-Holocene): Evidence for megalodontia and its palaeoecological implications

Body size is a useful character to unravel the biology of fossil taxa and, indirectly, the palaeoenvironment in which they lived. However, the reliability of size proxies is debated, particularly among insular endemics in which large teeth relative to body size have been observed. To shed light on this issue, here we compute statistical models to assess: (i) teeth and long bone scaling and (ii) dentition size evolutionary dynamics in the anagenetic lineage Prolagus figaro-P. sardus from the late Early Pleistocene-Holocene of Sardinia, Italy. Postcranial bones, particularly tibial epiphyses, are shown to be the most suitable parameters for prediction of body mass in Prolagus and other lagomorph taxa. By contrast, p3 should not be used for size reconstructions, whereas m1 width provided the highest correlation with long bones. On the other hand, the postcanine occlusal surface of Sardinian Prolagus (m1 and toothrow area) appeared significantly larger than those of extant lagomorphs, pointing to a higher resistance to tooth wear and a more durable permanent dentition. It seems likely that megalodontia might have evolved in Sardinian Prolagus to cope with the abrasive diet found on islands (food habit hypothesis). Nonetheless, we cannot exclude that other biological features, such as long longevity, could be co-driving forces in this fossil lineage (life history hypothesis). The results achieved throw light on size and scale evolution in lagomorphs, as well as refine the eco-evolutionary responses of small mammals to insular regimes.

Automated summary

Body size is a valuable trait for understanding the biology of fossil taxa and their paleoenvironment. In this study, statistical models were used to evaluate teeth and long bone scaling as well as dentition size evolutionary dynamics in the anagenetic lineage Prolagus figaro-P. sardus from Sardinia. Results suggest that postcranial bones are reliable predictors of body mass in Prolagus, while the occlusal surface of their teeth indicates a resistance to tooth wear and a durable dentition. Both food habit and life history hypotheses may explain the evolution of megalodontia in Sardinian Prolagus.