Kingdom Animalia Superfamily †Miacoidea Phylum Chordata | Class Mammalia Family †Viverravidae Rank Genus | |
Similar Viverravidae, Vulpavus, Miacoidea, Carnivoramorpha, Miacidae | ||
Didymictis is an extinct genus of carnivorous mammals known from the late Paleocene and early Eocene (Tiffanian-Gardnerbuttean NALMA) of North America. This genus in the family Viverravidae contains five species.
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Didymictis is the only viverravid for which there are considerable postcranial remains. The genus was primarily terrestrial but at least partly cursorial, similar to a civet.
Description
Didymictis has an elongated and relatively large skull with small and low braincase and a long and narrow basicranial region. The occipital and saggital crests are very high. The limbs are of moderate length with subdigitigrade and five-toed feet. The dentition (3.1.4.23.1.4.2) contrast those of miacids by the sharp differentiation between sectorial and tubercular dentition, the loss of the last molar and an elongated second molar, similar to the dentition in bears and raccoons.
Comparing Didymictis to Vulpavus, a much smaller and more agile viverravid, Heinrich & Rose 1997 noted that Didymictis' limbs, especially the hindlimb, are similar to those in extant carnivornas adapted for speed, and the forelimbs to some extent are specialized to digging. The authors concluded that Didymictis was a relatively specialized terrestrial carnivore capable of hunting with speed or pursuing by digging.
Species
D. proteus is known from the late Paleocene and earliest Eocene of Wyoming and the only species present in the Tiffanian and Clarkforkian stages (60–55 Ma). It is slightly larger than D. leptornylus and slightly smaller than D. protenus. Simpson 1937 named a new subspecies, Didymictis protenus proteus, which Polly 1997 reranked as the species D. proteus. Dorr 1952 described Didymictis dellensis which Gingerich & Winkler 1985 included in Protictis dellensis. Polly 1997 finally included these species in D. proteus.
D. leptomylus is known from the early Wasatchian (55 Ma) of western North America, but by far fewer specimens than D. proteus.
D. protenus is known from the earliest through late Wasatchian (early Eocene) of western North America. Cope assigned his specimen, "one entire and a portion of the other mandibular ramus, with teeth well preserved", to the creodont genus Limnocyon and named his new species L. protenus. Cope later created a new genus and renamed his species Didymictis protenus.
D. vancleveae is known from a fragmented jaw with several teeth (Colorado) described by Robinson 1966 and another tooth (Wyoming) tentatively assigned to this species. Robinson described D. vancleveae as larger than D. altidens and probably the youngest Didymicits. He assumed that the genus grew larger as it evolved.