A new species of Varalphadon (Mammalia, Metatheria, Sparassodonta) from the upper Cenomanian of southern Utah, North America: Phylogenetic and biogeographic insights

The origin of the South American Sparassodonta has always been debated. Current data indicate a North American origin for this group, but no definitive fossil evidence was recovered so far to prove this hypothesis. Herein, Varalphadon janetae sp. nov. is described from the upper Cenomanian and lower Coniacian of southern Utah, which represents the oldest known Sparassodonta. This taxon can be considered to represent Varalphadon as it presents a markedly mesiodistally compressed protocone and M3; small StA, flattened StD, slightly labial contact of the cristid obliqua, labially salient protoconid and lacks StC. It differs from other species of the genus in the smaller size, proportionally narrower protoconal area, paracone slightly more labial than metacone in M3, more labiolingually compressed StD, keeled metaconid and narrower hypoconid and talonid basin. Varalphadon shares with other sparassodonts the presence of vestigial cuspules between StB and StD, flattened and poorly developed StD, absent StC, straight centrocrista, crested conules and an m1 markedly smaller and strongly labiolingually compressed. The phylogenetic analysis recovered Varalphadon as a basal Sparassodonta, corroborating previous studies that considered this taxon as more basal than remaining “Alphadontidae”, which is represented by Protalphadon, Eoalphadon, Alphadon, Albertatherium and Nortedelphys. “Varalphadon” crebreforme is recovered as a Hatcheriformes. The results demonstrate that Metatheria originates in North America during the late Early Cretaceous, with Gondwanan lineages evolving in the Northern Hemisphere during the Late Cretaceous prior to their dispersal to South American millions of years later (late Maastrichtian?). The analysis recovered Metatheria as a Gondwanan invasive lineage.