''Boreogomphodon'' is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

traversodontid Traversodontidae is an extinct family of herbivorous cynodonts. Traversodonts were primarily Gondwanan, with many species known from Africa and South America. Recently, traversodonts have also been found from Europe and North America. Traversodon ...

cynodont Cynodontia () is a clade of eutheriodont therapsids that first appeared in the Late Permian (approximately 260 Megaannum, mya), and extensively diversified after the Permian–Triassic extinction event. Mammals are cynodonts, as are their extin ...

s from the

Late Triassic The Late Triassic is the third and final epoch (geology), epoch of the Triassic geologic time scale, Period in the geologic time scale, spanning the time between annum, Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch a ...

of the eastern

United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...

. Fossils have been found from the

Turkey Branch Formation The Doswell Formation (also known as the Doswell Group) is a geologic unit of Upper Triassic age, part of the Newark Supergroup. The Doswell Formation was originally named to refer to a geological sequence which forms the lower part of the sediment ...

Virginia Virginia, officially the Commonwealth of Virginia, is a U.S. state, state in the Southeastern United States, Southeastern and Mid-Atlantic (United States), Mid-Atlantic regions of the United States between the East Coast of the United States ...

and the

Pekin Formation The Pekin Formation is a Late Triassic (Carnian) geological Formation (geology), formation in North Carolina. The Pekin Formation is specific to the Sanford Sub-Basin of the Deep River Basin of North Carolina, although it may be equivalent to the ...

North Carolina North Carolina ( ) is a U.S. state, state in the Southeastern United States, Southeastern region of the United States. It is bordered by Virginia to the north, the Atlantic Ocean to the east, South Carolina to the south, Georgia (U.S. stat ...

Description and history

''Boreogomphodon jeffersoni'' was named in 1990. Its teeth and cranial bones are the most common tetrapod fossils in the Turkey Branch Formation. Remain assigned to ''B. jeffersoni'' are also known from the Pekin Formation of North Carolina. ''Boreogomphodon'' was distinguished from other traversodontids like the African '' Luangwa'' and the South American ''

Traversodon ''Traversodon'' is an extinct genus of cynodonts. It was a relative of the ancestor to modern mammals. ''Traversodon'' lived in what is now South America. Species ''Traversodon stahleckeri'' was first found by Friedrich von Huene in 1936 in the ...

'' on the basis of its postcanine teeth. Most traversodontids have lower postcanine teeth with two cusps, but ''Boreogomphodon'' was the first traversodontid found with three cusps on its lower postcanine teeth. There is a single cusp on the side of the upper postcanine facing the lip, while a flat surface extends outward from it. The traversodontid '' Arctotraversodon'' from the

Wolfville Formation The Wolfville Formation is a Triassic geologic formation of Nova Scotia. The formation is of Carnian to early Norian age. Fossils of small land vertebrates have been found in the formation, including procolophonid and early archosauromorph rep ...

Nova Scotia Nova Scotia is a Provinces and territories of Canada, province of Canada, located on its east coast. It is one of the three Maritime Canada, Maritime provinces and Population of Canada by province and territory, most populous province in Atlan ...

is similar to ''Boreogomphodon'' in that it has three cusps on its lower postcanine, but its postcanines are much wider than they are long relative to those of ''Boreogomphodon''. ''Boreogomphodon'' specimens likely represent juvenile individuals because of their small size. The snout is short, while larger, presumably mature traversodonts have longer snouts. ''Boreogomphodon'' specimens have only four or five postcanine teeth. Traversodontids acquire more of these teeth as they grow, suggesting that ''Boreogomphodon'' individuals were not fully mature. ''Boreogomphodon'' also has some sectorial, or cutting, postcanine teeth, which are not present in most larger traversodontids. ''Boreogomphodon'' has several primitive features, including a depression in the upper jaw called the paracanine fossa in front of the canine tooth. This fossa provides space for the lower canine tooth when the jaw is closed. Above the upper canine at the top of the snout there is a small depression on the

maxilla In vertebrates, the maxilla (: maxillae ) is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The two maxil ...

. The tip of the snout is covered in irregular pits, a unique feature of ''Boreogomphodon''. Each upper postcanine has large central cusp and a posterior cingulum.

Classification

''Boreogomphodon'' is closely related to ''Arctotraversodon'' and '' Nanogomphodon''. The three North American traversodontids form a somewhat basal

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

within Traversodontidae. Below is a

cladogram A cladogram (from Greek language, Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an Phylogenetic tree, evolutionary tree because it does not s ...

modified from Sues and Hopson (2010) showing the phylogenetic relations of ''Boreogomphodon'':

References

{{Taxonbar, from=Q4944941 Traversodontidae Late Triassic synapsids of North America Fossil taxa described in 1990