The classification of snouters within Mammalia

By now everyone is familiar with the snouters, fictional members of the clade Rhinogradentia. Originally described by Harald Stümpke, these animals were described prior to breakthroughs in genetic studies, and thus were not described as anything other than “shrew-like” (Stümpke 1961). Due to the near-total extinction of this clade, phylogenetic studies have been delayed considerably, and the clade is not featured in mammal wide studies (i.e. Stanhoppe 1998).

Luckily, a few Antarctic offshore clades have provided genetic evidence at long last.

As it appears, Rhinogradentia is sister taxa to Theria. They diverged from therians in the early Jurassic, possibly from forms akin to Vincelestes that once roamed Gondwanna. Because the only material we have is from marine worm-like species, we cannot say for certain about the divergence of the many extinct clades from the Hi-yi-yi archipelago, but judging by mutation rates we can assume that, just like placentals and crown birds, they diversified rapidly after the KT event.

For now, the evidence is limited, but it seems clear that these mammals were not only the product of adaptive radiation on islands, but likely joining other groups during the KT aftermath.

Geological evidence suggests that the Hi-yi-yi archipelago was often submerged across the Cenozoic (Cupcakke 2013), so who knows how many adaptive radiations these animals went through.

If only we had more…