Trithelodontidae
Encyclopedia
The tritheledontids, also known as ictidosaurs, were small to medium-sized (about 10 or 20 cm long) cynodont
s. They were extremely mammal
-like, highly specialized cynodonts, although they still retained a very few reptilian
anatomical traits. Tritheledontids were mainly carnivorous or insectivorous, though some species may have developed omnivorous traits. Their skeletons show that they had a close relationship to mammal
s. Tritheledontids or their closest relatives may have given rise to primitive mammals
. The tritheledontids were one of the longest lived non-mammalian therapsids, living from late Triassic
to the Jurassic
period. Tritheledontids became extinct in the Jurassic period, possible due to competition with prehistoric mammal
s such as the triconodonts
. They are known from finds in South America
and South Africa
, indicating that they may have only lived on the supercontinent
of Gondwanaland. The family Tritheledontidae was named by South African paleontologist Robert Broom
in 1912. The family is often misspelled "Trithelodontidae".
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. They were extremely mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
-like, highly specialized cynodonts, although they still retained a very few reptilian
Reptile
Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...
anatomical traits. Tritheledontids were mainly carnivorous or insectivorous, though some species may have developed omnivorous traits. Their skeletons show that they had a close relationship to mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s. Tritheledontids or their closest relatives may have given rise to primitive mammals
Mammaliaformes
Mammaliaformes is a clade that contains the mammals and their closest extinct relatives. Phylogenetically, it is defined as a clade including the most recent common ancestor of Sinoconodon, morganuconodonts, docodonts, Monotremata, Marsupialia, Placentalia, extinct members of this clade, and all...
. The tritheledontids were one of the longest lived non-mammalian therapsids, living from late 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...
to the Jurassic
Jurassic
The Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
period. Tritheledontids became extinct in the Jurassic period, possible due to competition with prehistoric mammal
Prehistoric mammal
Prehistoric mammals are groups of mammals that lived before humans developed writing. 164 million years ago, in the Jurassic period, Castorocauda lutrasimilis, a mammal-like animal weighing about 500 grams , had a full mammalian pelt, with guard hairs and under fur, webbed feet, and scales on the...
s such as the triconodonts
Triconodonta
Triconodonta is the generic name for a group of early mammals which were close relatives of the ancestors of all present-day mammals. Triconodonts lived between the Triassic and the Cretaceous. They are one of the groups that can be classified as mammals by any definition...
. They are known from finds in South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
and South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
, indicating that they may have only lived on the supercontinent
Supercontinent
In geology, a supercontinent is a landmass comprising more than one continental core, or craton. The assembly of cratons and accreted terranes that form Eurasia qualifies as a supercontinent today.-History:...
of Gondwanaland. The family Tritheledontidae was named by South African paleontologist Robert Broom
Robert Broom
Professor Robert Broom was a Scottish South African doctor and paleontologist. He qualified as a medical practitioner in 1895 and received his DSc in 1905 from the University of Glasgow...
in 1912. The family is often misspelled "Trithelodontidae".
Genera
- RiograndiaRiograndiaRiograndia is a genus of tritheledontid cynodont from the Late Triassic of South America. The type species is R. guaibensis. Riograndia guaibensis was estimated to have been about 15 cm long and 30 g in weight. Remains have been found in the Caturrita Formation of the geopark of Paleorrota...
(a primitive Tritheledontid) - Subfamily Thritheledontinae
- Chalimia
- DiarthrognathusDiarthrognathusDiarthrognathus was a genus of mammal-like reptiles, known from fossil evidence found in South Africa. The Diarthrognathus is of interest as it possesses a jaw structure that is similar to both mammals and reptiles, with a reptilian joint between the quadrate and articular in addition to the...
- ElliotheriumElliotheriumElliotherium is an extinct genus of cynodont which existed in South Africa during the upper Triassic period. The type species is Elliotherium kersteni....
- IrajatheriumIrajatheriumIrajatherium is a genus known only by the species Irajatherium hernadezi. . It's named in honor of Irajá Damiani Pinto.-Specie:...
- PachygenelusPachygenelusPachygenelus is an extinct genus of tritheledontid cynodont. Fossils have been found from the Karoo basin in South Africa and date back to the Early Jurassic....
- TrithelodonTrithelodonTrithelodon was an extinct genus of a group of mammal-like reptiles called cynodonts. Like cynodonts, Trithelodon had many traits shared by mammals. Trithelodon was probably an insectivore, and nocturnal....