Trirachodontidae
Encyclopedia
Trirachodontidae is an extinct family
of cynognathia
n cynodont
s from the Triassic
of China
and southern Africa
. Trirachodontids appeared during the Early Triassic
soon after the Permian-Triassic extinction event
and quickly spread over a wide geographic area in a comparatively brief amount of time from 250 to 237 million years ago.
Trirachodontids have wide skulls and short, narrow snouts. Two large holes called temporal fenestrae run along the back of the head and have a uniformly large width. Trirachodontids also have two large canine teeth and smaller cusped postcanines. Most of the features that distinguish trirachodonts from other cynodonts are found in their dentition.
Trirachodontids lived in semi-arid environments with seasonal rainfal. The bone structure of trirachodontids suggests that they grew quickly in seasons with high rainfall and slowly in less favorable seasons. One trirachodontid, Trirachodon
, has been found in association with complex burrow systems. These burrows were likely used by many individuals to hide from predators, raise young, or stay warm.
Two subfamilies of trirachodontids are recognized: Trirachodontinae from Africa and Sinognathidae from China. Below is a cladogram
from Gao et al. (2010) showing the phylogenetic relationships of trirachodontids:
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
of cynognathia
Cynognathia
The Cynognathians are one of the two major clades of the infraorder Eucynodontia, the other being the Probainognathians. Cynognathus, the most basal representative of the clade was a carnivore, unlike most cynognathians. The cynognathians were mostly mammal-like, but the subgroup Tritylodontids...
n 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...
s from the Triassic
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
of China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
and southern Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
. Trirachodontids appeared during the Early Triassic
Early Triassic
The Early Triassic is the first of three epochs of the Triassic period of the geologic timescale. It spans the time between 251 ± 0.4 Ma and 245 ± 1.5 Ma . Rocks from this epoch are collectively known as the Lower Triassic, which is a unit in chronostratigraphy...
soon after the Permian-Triassic extinction event
Permian-Triassic extinction event
The Permian–Triassic extinction event, informally known as the Great Dying, was an extinction event that occurred 252.28 Ma ago, forming the boundary between the Permian and Triassic geologic periods, as well as the Paleozoic and Mesozoic eras...
and quickly spread over a wide geographic area in a comparatively brief amount of time from 250 to 237 million years ago.
Trirachodontids have wide skulls and short, narrow snouts. Two large holes called temporal fenestrae run along the back of the head and have a uniformly large width. Trirachodontids also have two large canine teeth and smaller cusped postcanines. Most of the features that distinguish trirachodonts from other cynodonts are found in their dentition.
Trirachodontids lived in semi-arid environments with seasonal rainfal. The bone structure of trirachodontids suggests that they grew quickly in seasons with high rainfall and slowly in less favorable seasons. One trirachodontid, Trirachodon
Trirachodon
Trirachodon is an extinct genus of tritylodontoid cynodont. Fossils have been found from the Cynognathus Assemblage Zone of the Beaufort Group in South Africa, dating back to the Early and Middle Triassic.-Description:...
, has been found in association with complex burrow systems. These burrows were likely used by many individuals to hide from predators, raise young, or stay warm.
Two subfamilies of trirachodontids are recognized: Trirachodontinae from Africa and Sinognathidae from China. 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...
from Gao et al. (2010) showing the phylogenetic relationships of trirachodontids: