A New Mammal Skull from the Late Cretaceous of Romania and Phylogenetic Affinities of Kogaionid Multituberculates

Among the Late Cretaceous fossil sites of Europe, only those from the so-called Hateg Island in Transylvania, western Romania, are remarkable by their abundance in mammal remains. Curiously, all of them belong to a single family of multituberculates, the Kogaionidae, one of the rare families that survived the Cretaceous-Paleogene mass extinction in Europe. Kogaionids are mostly represented by isolated teeth except for three partial large skulls from the Maastrichtian Sanpetru Formation of the Hateg Basin that have been described from the Sanpetru locality as Kogaionon ungureanui and from the Pui locality as Barbatodon transylvanicus and Litovoi tholocephalos. Here we report for the first time the discovery of a partial skull associated with p4 of a small-sized kogaionid from the Nalat-Vad locality in the Sanpetru Formation that we refer to Kogaionon radulescui, sp. nov. An updated phylogenetic analysis, including seven Maastrichtian and Paleocene kogaionids is performed and confirms that Kogaionidae is a monophyletic clade at the base of Cimolodonta. Kogaionon differs from Barbatodon in its narrower snout, proportionally smaller P1, narrower anterior part of P4 with four similar-sized cusps in the middle row, more squared or rounded M1 with an anteroposteriorly longer lingual row, and shorter p4 (at least for K. radulescui). Litovoi tholocephalos is here considered to be a junior synonym of B. transylvanicus. Despite their Maastrichtian age, the very simple and conservative dental morphology of these Romanian kogaionids suggests that they originated from an eobaatarid-like ancestor dispersing from Asia or possibly already existing in Europe between the Barremian and Albian, 40 to 55 Ma earlier.

Automated summary

Among the Late Cretaceous fossil sites of Europe, only the Hateg Island in Transylvania, western Romania, stands out for its abundance of mammal remains, all belonging to the Kogaionidae family. A new species, Kogaionon radulescui, has been discovered in the Sanpetru Formation. Phylogenetic analysis confirms Kogaionidae as a monophyletic clade at the base of Cimolodonta. The dental morphology of Romanian kogaionids suggests their origin from an eobaatarid-like ancestor originating from Asia or possibly existing in Europe much earlier.