''Triisodon'' is a genus of extinct

mesonychia Mesonychia ("middle claws") is an extinct taxon of small- to large-sized carnivorous ungulates related to artiodactyls. Mesonychids first appeared in the early Paleocene, went into a sharp decline at the end of the Eocene, and died out entirely ...

n mammal that existed during the Early

Paleocene The Paleocene, ( ) or Palaeocene, is a geological epoch that lasted from about 66 to 56 million years ago (mya). It is the first epoch of the Paleogene Period in the modern Cenozoic Era. The name is a combination of the Ancient Greek ''pal ...

New Mexico ) , population_demonym = New Mexican ( es, Neomexicano, Neomejicano, Nuevo Mexicano) , seat = Santa Fe, New Mexico, Santa Fe , LargestCity = Albuquerque, New Mexico, Albuquerque , LargestMetro = Albuquerque metropolitan area, Tiguex , Offi ...

, North America. The genus was named by Edward Drinker Cope in 1881 as a member of the Acreodi, a now invalid taxon that encompassed both

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 anc ...

s and mesonychians. The premolar teeth have three points, hence the generic name (tri=three, don=tooth). Cope described the type specimen of ''T. quivirensis'' as "about the size of a wolf." A smaller species has also been identified from the same region. Since material from this genus is incomplete, the exact size of adults and whether they showed sexual dimorphism or regional variations in size is unknown. ''Triisodon'' is the

type genus In biological taxonomy, the type genus is the genus which defines a biological family and the root of the family name. Zoological nomenclature According to the International Code of Zoological Nomenclature, "The name-bearing type of a nomina ...

of the family

Triisodontidae Triisodontidae is an extinct, probably paraphyletic, or possibly invalid family of mesonychian placental mammals. Most triisodontid genera lived during the Paleocene in North America, but the genus ''Andrewsarchus'' (if it is a mesonychian, an ...

, one of the three families within Mesonychia (the other two being

Mesonychidae Mesonychidae (meaning "middle claws") is an extinct family of small to large-sized omnivorous-carnivorous mammals. They were endemic to North America and Eurasia during the Early Paleocene to the Early Oligocene, and were the earliest group of l ...

and

Hapalodectidae Hapalodectidae (literal translation 'soft biters': ('soft, tender'), ('biter')) is an extinct family of relatively small-bodied () mesonychian placental mammals from the Paleocene and Eocene of North America and Asia. Hapalodectids differ fr ...

). Other North American triisodontid genera, including ''Goniacodon'', ''Eoconodon'', and ''Stelocyon'', have been referred to ''Triisodon''. Like many very early mammals, the relationship of triisonodontines to other living and fossil mammals has been uncertain, but most paleontologists currently consider them either mesonychids or the sister group of mesonychids, part of the stem group that led to

artiodactyls The even-toed ungulates (Artiodactyla , ) are ungulates—hoofed animals—which bear weight equally on two (an even number) of their five toes: the third and fourth. The other three toes are either present, absent, vestigial, or pointing poster ...

(including

whales Whales are a widely distributed and diverse group of fully aquatic placental marine mammals. As an informal and colloquial grouping, they correspond to large members of the infraorder Cetacea, i.e. all cetaceans apart from dolphins a ...

) and the ancient South American ungulates.

Species

*Genus ''Triisodon'' **''Trisonodon crassicuspus (= T. rusticus, Goniacodon, “Conoryctes”)'' ***Lower Paleocene (Torrejonian). Much smaller than ''T. quivirensis'' and with more elongate third promolar; distinguished from ''Eoconodon'' by having a somewhat reduced third molar. **''Triisodon quivirensis (= T. antiquus)'' ***Lower Paleocene (Torrejonian), coexisted in the same habitat with ''T crassicuspus.'' Distinguished from ''T. crassicuspus'' by much larger size, from ''Eoconodon'' as above. **''Triisodon heilprinianus'' identified by Cope, 1882 on the basis of a single molar, has since been referred to multiple groups. Referred to ''Eoconodon coryphaeus'' by Kondrashov and Lucas 2006.

References

External links

Paleo Biology
{{Taxonbar, from=Q2602946 Mesonychids Paleocene mammals Fossil taxa described in 1881 Paleocene mammals of North America Prehistoric placental genera