Boreogomphodon
Encyclopedia
Boreogomphodon is a genus
of traversodontid cynodont
from the Late Triassic
of the eastern United States
. Fossils have been found from the Turkey Branch Formation in Virginia
.
and the South American Traversodon
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
of Nova Scotia
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
. 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
.
. The three North American traversodontids form a somewhat basal
clade
within Traversodontidae. Below is a cladogram
modified from Sues and Hopson (2010) showing the phylogenetic relations of Boreogomphodon:
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of traversodontid cynodont
Cynodont
Cynodontia or cynodonts are a taxon of therapsids which first appeared in the Late Permian and were eventually distributed throughout all seven continents by the Early Triassic . This clade includes modern mammals and their extinct close relatives. They were one of the most diverse groups of...
from the Late Triassic
Late Triassic
The Late Triassic is in the geologic timescale the third and final of three epochs of the Triassic period. The corresponding series is known as the Upper Triassic. In the past it was sometimes called the Keuper, after a German lithostratigraphic group that has a roughly corresponding age...
of the eastern United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
. Fossils have been found from the Turkey Branch Formation in Virginia
Virginia
The Commonwealth of Virginia , is a U.S. state on the Atlantic Coast of the Southern United States. Virginia is nicknamed the "Old Dominion" and sometimes the "Mother of Presidents" after the eight U.S. presidents born there...
.
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. Boreogomphodon was distinguished from other traversodontids like the African LuangwaLuangwa
Luangwa may refer to:*Luangwa River, the major river of eastern Zambia;*the Luangwa Bridge, which crosses the Luangwa River*the Luangwa Valley, a rift valley branch of the Great Rift Valley, named after the Luangwa River flowing in it;...
and the South American Traversodon
Traversodon
Traversodon is a genus of therapsid. Being a cynodont, it was a relative of the direct ancestor to modern mammals. Traversodon lived in what is now the Northeastern part of the United States and South America.-Species:...
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
Arctotraversodon
Arctotraversodon is a genus of traversodontid cynodont from the Late Triassic of Canada. Fossils first described from the Wolfville Formation in Nova Scotia in 1984 and represented the first known traversodontid from North America. The type and only species is A...
from the Wolfville Formation
Wolfville Formation
The Wolfville Formation is a Mesozoic geologic formation of Nova Scotia. The formation is late Carnian to early Norian in age. Fossils of small land vertebrates have been found in the formation, including procolophonid and early archosauromorph reptiles and cynodonts...
of Nova Scotia
Nova Scotia
Nova Scotia is one of Canada's three Maritime provinces and is the most populous province in Atlantic Canada. The name of the province is Latin for "New Scotland," but "Nova Scotia" is the recognized, English-language name of the province. The provincial capital is Halifax. Nova Scotia is the...
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
Maxilla
The maxilla is a fusion of two bones along the palatal fissure that form the upper jaw. This is similar to the mandible , which is also a fusion of two halves at the mental symphysis. Sometimes The maxilla (plural: maxillae) is a fusion of two bones along the palatal fissure that form the upper...
. 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
Cingulum (tooth)
In dentistry, cingulum refers to an anatomical feature of the anterior teeth . It refers to the portion of the teeth, occurring on the lingual or palatal aspects, that forms a convex protuberance at the cervical third of the anatomic crown. It represents the lingual or palatal developmental lobe...
.
Classification
Boreogomphodon is closely related to Arctotraversodon and NanogomphodonNanogomphodon
Nanogomphodon is an extinct genus of synapsid which existed in Germany during the Middle Triassic period.Nanogomphodon were small herbivorous traversodontid gomphodonts. The type species is Nanogomphodon wildi...
. The three North American traversodontids form a somewhat basal
Basal (phylogenetics)
In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...
clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
within Traversodontidae. Below is a cladogram
Cladogram
A cladogram is a diagram used in cladistics which shows ancestral relations between organisms, to represent the evolutionary tree of life. Although traditionally such cladograms were generated largely on the basis of morphological characters, DNA and RNA sequencing data and computational...
modified from Sues and Hopson (2010) showing the phylogenetic relations of Boreogomphodon: