Abstract
Dental characters are importantly used for reconstructing the evolutionary history of mammals, because teeth represent the most abundant material available for the fossil species. However, the characteristics of dental renewal are presently poorly used, probably because dental formulae are frequently not properly established, whereas they could be of high interest for evolutionary and developmental issues. One of the oldest rodent families, the Ctenodactylidae, is intriguing in having longstanding disputed dental formulae. Here, we investigated 70 skulls among all extant ctenodactylid genera (Ctenodactylus, Felovia, Massoutiera and Pectinator) by using X-ray conventional and synchrotron microtomography in order to solve and discuss these dental issues. Our study clearly indicates that Massoutiera, Felovia and Ctenodactylus differ from Pectinator not only by a more derived dentition, but also by a more derived eruptive sequence. In addition to molars, their dentition only includes the fourth deciduous premolars, and no longer bears permanent premolars, conversely to Pectinator. Moreover, we found that these premolars are lost during adulthood, because of mesial drift of molars. Mesial drift is a striking mechanism involving migration of teeth allowed by both bone remodeling and dental resorption. This dental innovation is to date poorly known in rodents, since it is only the second report described. Interestingly, we noted that dental drift in rodents is always associated with high-crowned teeth favoring molar size enlargement. It can thus represent another adaptation to withstand high wear, inasmuch as these rodents inhabit desert environments where dust is abundant. A more accurate study of mesial drift in rodents would be very promising from evolutionary, biological and orthodontic points of view.
Highlights
The interest of studying rodents among all mammals is stressed by their ecological ubiquity, coupled to their flourishing diversity
We strictly focused our observations on the number and replacement of cheek teeth for each genus of extant ctenodactylids (Fig. 2)
The investigated neonate skull (misidentified specimen: ‘‘C. gundi’’ Museum National d’Histoire Naturelle (MNHN)-CG2006-198, (e.g. [18])) includes alveoli of dP3, in addition to dP4 and M1, but it does not display any evidence for the presence of dP3
Summary
The interest of studying rodents among all mammals is stressed by their ecological ubiquity, coupled to their flourishing diversity (about 2300 species [1]). The evolutionary success of rodents is probably due to their small size, their high reproductive rates, their short breeding cycle, and their extensive range of dental characteristics These dental particularities notably rely on the very high number of crown morphologies [2,3,4], enamel microstructure patterns [5,6], and masticatory functions [7,8,9]. We lack a global view regarding the diversity of mechanisms associated with rodent dentitions, and only rare discoveries showed very innovative dental systems in rodents [14] In this context, this study aims at better understanding the underlying mechanisms of the establishment and replacement of the dentition of gundis (Ctenodactylidae), whose extant species present peculiar dental formulae. Their study might permit the opening of a new window on the knowledge of these dental issues
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