Herpetotherium is an extinctgenus ofmetatherian mammal, belonging to the possiblyparaphyletic familyHerpetotheriidae. Native to North America from theEocene to EarlyMiocene,fossils have been found inCalifornia,Oregon,Texas,Florida,Montana,Wyoming,Colorado,North andSouth Dakota,Nebraska, andSaskatchewan.[1] The oldest species,H. knighti, is dated to around 50.3mya,[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 foundHerpetotherium to be the sister group to extant marsupials.[3] It is the youngest known metatherian from North America until the migration of theVirginia opossum from South America within the last 2 million years.[4]
Herpetotherium fugax
Some authors have regarded the species assigned toHerpetotherium (for instance,H. comstocki,H. marsupium, andH. merriami) as belonging to African and European genusPeratherium Aymard, 1850 on the basis of Simpson's observation that "the upper molars ... agree closely withPeratherium, less closely with other didelphid genera" and on Cope himself recognizing "there is no valid distinction betweenHerpetotherium andPeratherium" (Simpson, 1928, p. 6)[5][6][7] Yet other authors have continued to maintain generic separation forHerpetotherium and continue to assign new North American species of herpetotheriid marsupials to this genus.[8][9][10][11]
H. knighti (syn.Centracodon delicatus,Entomacodon minutus,Peratherium morrisi)
H. marsupium Troxell, 1923, p. 508[12] (syn.Peratherium marsupium according to Simpson, 1928[13][14])
H. merriami (Stock and Furlong, 1922, originally named withinPeratherium as Stock agreed with Simpson thatHerpetotherium Cope 1873 was synonymous withPeratherium)
Herpetotherium has long been recognized as having a primitive morphology compared to other marsupials. For instance, Osborn (1907, p. 111) thought it represented an ancestral stock to both "later carnivorous and herbivorous types of marsupials", and thought it was evidence that polyprotodont opossum-like mammals must have given rise to other marsupials (Osborn, 1910, p. 154). Troxell (1923) strongly fixated on mandibular characters ofHerpetotherium (though speaking specifically ofH. marsupium, yet these are generally true ofHerpetotherium) that he felt were especially comparable toDidelphis, such as "(1) the strong canine, (2) weak anterior premolar, (3) dominance of theprotocone in the premolars, (4) fourth tooth of the series molariform, (5) position ofmental foramen under this tooth, (6) identical form of the molars, (7) groove on the jaw suggesting an inflected angle," yet he pointed out several differences, such as "(1) absence ofdiastemata around the anterior premolar, (2) trend of the mental foramen forward instead of backward, (3) the inflected angle, seeming to begin beneath the molars" (p. 510).
^Stock, Chester. "Sespe Eocene Didelphids."Proceedings of the National Academy of Sciences, pp. 122-124, 1935. [Peratherium californicum sp. nov. No. 1943 Calif. Inst. Tech. Vert. Pale. Coll.]
^Krishtalka and Stucky, 1983, p. 232 provides a complete review of synonymy
^Rothecker, Jennifer, and John E. Storer. "The Marsupials of the Lac Pelletier Lower Fauna, Middle Eocene (Duchesnean) of Saskatchewan."Journal of Vertebrate Paleontology, vol. 16, no. 4, pp. 770-774, December 1996.
^West, Robert M. "Fossil mammals from the Lower Buck Hill Group, Eocene of Trans-Peco Texas: Marsupicarnivora, Primates, Taeniodonta, Condylarthra, Bunodont Artiodactyla, and Dinocerata."The Pearce-Sellard Series [Occasional publication of the Texas Memorial Museum, The University of Texas at Austin], no. 35, October 15, 1982.
^Korth, William W., and Jennifer Cavin. "New material of the marsupial (Mammalia, Metatheria) Herpetotherium merriami (Stock and Furlong, 1922) from the John Day Formation, late Oligocene, Oregon, USA." J. Paleontology, vol. 90, no. 6, pp. 1225-1232, 2016.
^Troxell, Edward Leffingwell."A New Marsupial."American Journal of Science, vol. V, no. 30, article XLI, pp. 507-511, 1923.
