Reassessment of the small ‘arctocyonid’ Prolatidens waudruae from the early Paleocene of Belgium, and its phylogenetic relationships with ungulate-like mammals

ABSTRACT

‘Arctocyonids’ are generally considered as including some of the most primitive ‘ungulates’ from the Paleocene. Although more than 15 genera are known from North America, European members of this order are less common and mainly belong to derived genera such as Arctocyon. However, one species of primitive arctocyonid, Prolatidens waudruae, was described from the early Paleocene of Hainin, Mons Basin, Belgium. Here we describe new dental positions of this small taxon, including for the first time upper molars and upper fourth premolar. Morphological comparisons confirm the position of P. waudruae among primitive ‘ungulates,’ with the closest North American arctocyonids being Prothryptacodon furens and Oxyprimus galadrielae. Oxyprimus galadrielae features slightly more primitive morphological traits than both other species. Apheliscids share several characters with Prolatidens, but the latter lacks the apomorphies defining the family. Among ‘arctocyonids,’ Prolatidens shares with only Protungulatum and Oxyprimus the incomplete lingual cingulum at the base of the protocone of M1. Prolatidens waudruae is unique among Procreodi in its combination of primitive and derived characters. The cladistic analysis places P. waudruae close to the base of the ingroup, indicating that this species is among the most primitive members of the Paleocene ‘ungulates.’ However, the lower nodes of the trees are not well supported and definitive conclusions should await more complete specimens and analysis. Apheliscids are situated relatively far from Prolatidens, suggesting that the resemblances between them are better considered as convergences. Based on the morphological comparisons, the arctocyonid from Hainin correlates best with North American Torrejonian taxa.

ACKNOWLEDGMENTS

We warmly thank B. Sigé (Université de Montpellier II, France) who initiated the study of the mammals from Hainin and B. Marandat (Université de Montpellier II, France) for the preparation of the specimens. We gratefully acknowledge R. Smith (Royal Belgian Institute of Natural Sciences, Brussels, Belgium) and G. Gunnell (Duke Lemur Center, Durham, North Carolina, U.S.A.) for access to cast collections. At the Royal Belgian Institute of Natural Sciences, A. Folie coordinated the management of the Hainin collection, and J. Cillis helped in producing the SEM photographs. Financial support for this research was provided by the Belgian Federal Science Policy Office (doctoral fellowship to E.D. and project MO/36/020 to T.S.).

Handling editor: Thomas Martin.