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Didymictis ("double weasel") is an extinct genus of placental mammals from extinct subfamily Didymictinae within extinct family Viverravidae, that lived in North America and Europe from the late Paleocene to middle Eocene.J. J. Flynn (1998.) "Early Cenozoic Carnivora ("Miacoidea")." In C. M. Janis, K. M. Scott, and L. L. Jacobs ( eds.) "Evolution of Tertiary Mammals of North America. Volume 1: Terrestrial Carnivores, Ungulates, and Ungulatelike Mammals." Cambridge University Press, Cambridge.
Didymictis had an elongated and relatively large skull with small and low braincase and a long and narrow basicranial region. The occipital and sagittal crests are very high. The limbs are of moderate length with subdigitigrade and five-toed feet. The dentition () contrasts those of basal Carnivoraformes 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 carnivoraform, Heinrich and Rose in 1997 noted that Didymictis' limbs, especially the hindlimb, are similar to those in extant carnivorans 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.
D. proteus is known from the late Paleocene and earliest Eocene of Wyoming and the only species present in the Tiffanian and Clarkforkian stages. It is slightly larger than D. leptornylus and slightly smaller than D. protenus. Simpson in 1937 named a new subspecies, Didymictis protenus proteus, which Polly in 1997 reranked as the species D. proteus. Dorr in 1952 described Didymictis dellensis, which Gingerich and Winkler in 1985 included in Protictis dellensis.P. D. Gingerich and D. A. Winkler (1985) "Systematics of Paleocene Viverravidae (Mammalia, Carnivora) in the Bighorn Basin and Clark's Fork Basin, Wyoming." Contributions from the Museum of Paleontology, University of Michigan 27(4):87-128 Polly in 1997 finally included these species in D. proteus.
D. leptomylus is known from the early Wasatchian of western North America, but by far fewer specimens than D. proteus.
D. vancleveae is known from a fragmented jaw with several teeth (Colorado) described by Robinson in 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.
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