Résumé
Cenozoic Laurasian ‘opossum-like’ marsupialiforms, Peradectidae (Crochet, 1979) and Herpetotheriidae (Trouessart, 1879), are extinct taxa mostly known from isolated tribosphenic molars. Their blurred evolutionary histories are marked by subtle and often homoplastic morphological character state transformations. However, disentangling these phylogenetic affinities is essential for a comprehensive understanding of metatherian evolution. Here, we introduce a novel matrix of dental characters, with taxon sampling focused on the crucial periods preceding and following the Cretaceous/Paleogene boundary, in an attempt to unravel the phylogenetic positions of peradectids and herpetotheriids within Metatheria, and the intrafamilial relationships of peradectids. Parsimony and Bayesian analyses reveal that all the studied Cenozoic marsupialiforms assemble into a clade, identified as Notometatheria, thereby confirming that metatherians were heavily impacted by the K–Pg mass extinction. The crucial positions of the enigmatic early Paleocene genera Thylacodon Matthew and Granger, 1921, and Swaindelphys Johanson, 1996, allow us to identify a rapid, possibly Paleocene, North American divergence of peradectids and herpetotheriids. For the first time, a monophyletic Peradectidae, encompassing 22 North American and European species allocated to this family to date, is found in a broad spatiotemporal and taxonomic context. Reconstructing the sequence of appearance of dental features within Peradectidae enables us to characterize each phase of their morphological evolution and refine their complex systematics. All known European peradectid species are assigned to Europeradectes Gernelle gen. nov., including the new late early Eocene Europeradectes marivauxi Gernelle and Europeradectes williamsoni Gernelle. In light of the phylogenetic framework providing the synapomorphies of unequivocal peradectids, our revision of all currently available specimens previously ascribed to or putatively allied with Peradectidae from South America, Africa, and Asia shows that this family was most likely endemic to North America and Europe throughout its evolutionary history. These results emphasize the pivotal role of comparative dental anatomy in understanding the evolution and ultimately the palaeobiogeography of metatherians, especially for taxa exhibiting apparently conservative morphology.