Ontogenetic skull development and paleobiology of the tragulid Dorcatherium naui (Mammalia: Artiodactyla) from the early Late Miocene hominid locality Hammerschmiede (Germany)

Ontogeny describes the individual developmental history of an organism across its lifetime. Comparative ontogenetic approaches can be applied to closely related taxa and provide a powerful framework for investigating evolutionary changes in morphology, life history, and developmental timing between fossil and extant relatives. This approach is particularly informative for the fossil chevrotain Dorcatherium naui and the extant African water chevrotain Hyemoschus aquaticus , which are consistently recovered as sister taxa in phylogenetic analyses. Until recently, the fossil record of D. naui was sparse, despite the fact that this species represents the type species of one of the most frequently cited fossil tragulid genera. Here we demonstrate that the life history and ecological characteristics, as sexual maturity, sexual size dimorphism, reproduction rate and maximum life span, inferred for fossil D. naui share numerous similarities with those of extant H. aquaticus , supporting a close phylogenetic relationship between both taxa. However, we find that D. naui might have lived in more open riparian woodlands, compared to its extant relative. In addition, our results provide evidence for a paedomorphic condition of cranial ornamentation in H. aquaticus relative to D. naui . Together, these findings support the use of H. aquaticus as a suitable modern analogue for fossil tragulids in general, and for Dorcatherium in particular. Moreover, the observed similarities between both taxa are consistent with a paleobiogeographic scenario involving a dispersal event of an ancestral form morphologically similar to D. naui from Eurasia into Africa during the Late Miocene, followed by independent evolution culminating in the emergence of H. aquaticus during the Pliocene.