''Didymictis'' ("double

weasel Weasels are mammals of the genus ''Mustela'' of the family Mustelidae. The genus ''Mustela'' includes the least weasels, polecats, stoats, ferrets and European mink. Members of this genus are small, active predators, with long and slender bo ...

") is an

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

of placental mammals from extinct subfamily

Didymictinae Didymictinae ("double weasels") is an extinct subfamily of mammals from extinct family Viverravidae, that lived from the early Palaeocene to the middle Eocene in North America and Europe. Classification and phylogeny Classification * Subfami ...

within extinct family

Viverravidae Viverravidae ("ancestors of viverrids") is an extinct monophyletic family of mammals from extinct superfamily Viverravoidea within the clade Carnivoramorpha, that lived from the early Palaeocene to the late Eocene in North America, Europe and As ...

, that lived in

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

and

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...

from the late

Paleocene The Paleocene, ( ) or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), E ...

to middle

Eocene The Eocene ( ) Epoch is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene' ...

Description

''Didymictis'' is the only viverravid genus for which there are considerable postcranial remains. The genus was primarily terrestrial but at least partly cursorial, similar to a

civets A civet () is a small, lean, mostly nocturnal mammal native to tropical Asia and Africa, especially the tropical forests. The term civet applies to over a dozen different species, mostly from the family Viverridae. Most of the species diversity ...

. ''Didymictis'' has 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 () contrast those of basal carnivoraforms 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 Bears are carnivoran mammals of the family Ursidae. They are classified as caniforms, or doglike carnivorans. Although only eight species of bears are extant, they are widespread, appearing in a wide variety of habitats throughout the North ...

and

raccoons The raccoon ( or , ''Procyon lotor''), sometimes called the common raccoon to distinguish it from other species, is a mammal native to North America. It is the largest of the procyonid family, having a body length of , and a body weight of . ...

. Comparing ''Didymictis'' to ''

Vulpavus ''Vulpavus'' ("fox grandfather") is an extinct genus of Miacidae Miacids are extinct primitive carnivoramorphans within the family Miacidae that lived during the Paleocene and Eocene epochs, about 62–34 million years ago. Miacids exist ...

'', 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 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.

Classification and phylogeny

History of species and classification

''D. protenus'' is known from the earliest through late

Wasatchian The Wasatchian North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 55,400,000 to 50,300,000 years BP lasting . It is usually c ...

(early Eocene) of western North America.

Cope The cope (known in Latin as ''pluviale'' 'rain coat' or ''cappa'' 'cape') is a liturgical vestment, more precisely a long mantle or cloak, open in front and fastened at the breast with a band or clasp. It may be of any liturgical colours, litu ...

assigned his specimen, "one entire and a portion of the other mandibular ramus, with teeth well preserved", to the

creodont Creodonta ("meat teeth") is a former order of extinct carnivorous placental mammals that lived from the early Paleocene to the late Miocene epochs in North America, Europe, Asia and Africa. Originally thought to be a single group of animals ance ...

genus '' Limnocyon'' and named his new species ''L. protenus''. Cope later created a new genus and renamed his species ''Didymictis protenus''. ''D. proteus'' is known from the late Paleocene and earliest Eocene of Wyoming and the only species present in the

Tiffanian The Tiffanian North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 60,200,000 to 56,800,000 years BP lasting . It is usually c ...

and

Clarkforkian The Clarkforkian North American Stage, on the geologic timescale, is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 56,800,000 to 55,400,000 years BP lasting . Considered t ...

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''. 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 n 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.

Taxonomy

Phylogeny

The phylogenetic relationships of genus ''Didymictis'' are shown in the following cladogram: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):87-128P. D. Polly (1997
"Ancestry and Species Definition in Paleontology: A Stratocladistic Analysis of Paleocene-Eocene Viverravidae (Mammalia, Carnivora) from Wyoming."
Contributions from the Museum of Paleontology, University of Michigan 30(1):1-53S. Faurby, L. Werdelin, A. Antonelli (2019
"Dispersal ability predicts evolutionary success among mammalian carnivores"
Department of Biological and Environmental Sciences, University of Gothenburg, Box 461, SE

References

External links

* {{Taxonbar, from=Q5274262 Viverravids Paleocene mammals Paleocene mammals of North America Prehistoric placental genera