The evolution and ontogeny of the dentition of Myotragus balearicus Bate, 1909 (Artiodactyla, Caprinae): evidence from new fossil data

Abstract

Myotragus balearicus Bate 1909 is an artiodactyl Caprinae endemic to the Balearic Islands (Spain), which became extinct more than 4000 years ago. It is characterized by a series of very unusual apomorphies acquired throughout its insular evolution, one of which is the presence of a single evergrowing incisor (with an open root) in each dentary. This incisor has been classically considered as I. The study of recently discovered fossils of this species, which have been collected from the excavation of Holocene cave sediments in Cova Estreta (Pollença, Mallorca) and in Cova des Moro (Manacor, Mallorca), together with the re-examination of materials belonging both to this species and to its ancestors, allowed us to study the ontogeny and evolution of the Myotragus dentition. The replacement of premolars differs only slightly from the pattern recorded in other bovids. Nevertheless, there are significant differences with other bovids regarding the incisiform series. Myotragus balearicus lacks secondary incisors. Through a neotenic process, which started during the Upper Pliocene, M. balearicus acquired a monophyodontic incisiform dentition, reducing the number of incisiforms to only one, identified as dI2. The richness of the finds allows us to describe the different steps in this evolution. The only incisiform that appears to have been lost is dI3. The identification of the evergrowing incisor of M. balearicus as dI2reinforces its convergence with rodents postulated by Bate and there is discussion regarding homologies of incisors of rodents and lagomorphs.