Herpetotherium
Herpetotherium
Extinct genus of metatherian mammals
Herpetotherium is an extinct genus of metatherian mammal, belonging to the possibly paraphyletic family Herpetotheriidae. Native to North America from the Eocene to Early Miocene, fossils have been found in California, Oregon, Texas, Florida, Montana, Wyoming, Colorado, North and South Dakota, Nebraska, and Saskatchewan.[1] The oldest species, H. knighti, is dated to around 50.3 mya,[2] and the most recent, an unnamed species, may be as recent as 15.97 mya.[1] A morphological analysis of marsupials and basal metatherians conducted in 2007 found Herpetotherium to be the sister group to extant marsupials.[3] It is the youngest known metatherian from North America until the migration of the Virginia opossum from South America within the last 2 million years.[4]
Some authors have regarded the species assigned to Herpetotherium (for instance, H. comstocki, H. marsupium, and H. merriami) as belonging to African and European genus Peratherium Aymard, 1850 on the basis of Simpson's observation that "the upper molars ... agree closely with Peratherium, less closely with other didelphid genera" and on Cope himself recognizing "there is no valid distinction between Herpetotherium and Peratherium" (Simpson, 1928, p. 6) [5][6][7] Yet other authors have continued to maintain generic separation for Herpetotherium and continue to assign new North American species of herpetotheriid marsupials to this genus.[8][9][10][11]
