Revision of the genus Protadelomys, a middle Eocene theridomyoid rodent: evolutionary and biochronological implications

Abstract

Abstract The generic status of the species referred to Protadelomys has long been problematic. Most Protadelomys species are now considered paraphyletic, except for the type species P. cartieri and for P. lugdunensis. Here, we revised these two species from their type locality, Egerkingen (Swiss Jura) for P. cartieri and Lissieu (Rhône, France) for P. lugdunensis. For the latter species, we also consider the locality of Laprade (Tarn-et-Garonne, Quercy, France). Additionally, we revised the material attributed to Protadelomys species that is now considered paraphyletic: ?P. alsaticus from Bouxwiller (Bas-Rhin, France) and Cuzal (Lot, Quercy, France), ?P. maximini from St-Maximin (Gard, France), and ?P. nievesae from Casa Ramon (Huesca, Spain). Our detailed morphological analysis enables us to better characterize the extent of the morphological and size variability in all Protadelomys and ?Protadelomys species. We show that both P. cartieri and P. lugdunensis co-existed in Egerkingen, Lissieu, and Laprade. We also erected a new genus and species, Homœtreposciurus egerkingensis, and reported the presence of Eoelfomys from Egerkingen. Eoelfomys is here described as a new genus and species from Laprade. Size and morphological comparisons enabled us to detect large intraspecific variation in the material of ?P. alsaticus from Bouxwiller, as well as in the type population of ?P. maximini. The co-occurrence of the two Protadelomys species, at least in two localities, in addition to the revision of the features characterizing the three species of ?Protadelomys, led us to question the existence of a single evolutionary lineage (chronospecies), as previously recognized from ?P. maximini to P. lugdunensis.

Keywords

• Theridomorphs
• Protadelomys
• Dental morphologic and size variability
• Systematics
• Lutetian biochronology