Sinopa rapax (Leidy 1871; Eocene-Early Oligocene; 50mya) was traditionally considered a creodont or sometimes ‘provivverine’ relative of Hyaenodon, but here nests between Dasyurus and Sarcophilus (Fig. 1). It is similar in size to these extant taxa. Not sure about those premaxillary teeth. The dentary canines are larger than the maxillary canines.
otter-like Palaeosinopa (Matthew 1901) was first considered a creodont, then a fish-eating pantolestid insectivore (it does get crazy here), but now in the large reptile tree (LRT) nests with eutherian (placental) aquatic seals. like Phoca.
The marsupial Sinopa is not related
to Palaeosinopa, the ancestor to seals. Instead Sinopa is one more creodont nesting in the Marsupialia, still… very close to the basalmost clade in the Placentalia (Eutheria), the Carnivora. We’ll discuss creodonts soon.
Leidy J 1871. Remains of extinct mammals from Wyoming. Proceedings of the Academy of Natural Sciences Philadelphia1871:113–117.