Tritylodontids were small to medium-sized, highly specialized and 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 cynodonts. They were the last family of the non-mammalian synapsids. One of the last cynodont lines to appear, the Tritylodontidae descended from a Cynognathus

Cynognathus

Cynognathus crateronotus was a meter-long predator of the Early to Middle Triassic. It was among the more mammal-like of the Synapsids, a member of a grouping called Eucynodontia. The genus Cynognathus had an almost worldwide distribution...

-like cynodont. The Tritylodontids were herbivorous, chewing through vegetation

Vegetation

Vegetation is a general term for the plant life of a region; it refers to the ground cover provided by plants. It is a general term, without specific reference to particular taxa, life forms, structure, spatial extent, or any other specific botanical or geographic characteristics. It is broader...

, such as stem

Plant stem

A stem is one of two main structural axes of a vascular plant. The stem is normally divided into nodes and internodes, the nodes hold buds which grow into one or more leaves, inflorescence , conifer cones, roots, other stems etc. The internodes distance one node from another...

s, leaves

Leaves

-History:Vocalist Arnar Gudjonsson was formerly the guitarist with Mower, and he was joined by Hallur Hallsson , Arnar Ólafsson , Bjarni Grímsson , and Andri Ásgrímsson . Late in 2001 they played with Emiliana Torrini and drew early praise from the New York Times...

, and root

Root

In vascular plants, the root is the organ of a plant that typically lies below the surface of the soil. This is not always the case, however, since a root can also be aerial or aerating . Furthermore, a stem normally occurring below ground is not exceptional either...

s. Some scientists believe that the mammals arose from this group of cynodonts, however, some say that mammals arose from the Tritheledontidae, another group of specialized 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. One of the interesting facts about the Tritylodontids is that they are the longest living of all the non-mammalian therapsids. They appeared in the latest 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...

 period, and persisted through 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...

 until the Middle Cretaceous

Cretaceous

The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...

. This shows that the Tritylodontids were a very successful group of therapsids, even though they lived right beneath the ruling dinosaur

Dinosaur

Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...

s' feet. No one knows why the Tritylodontids went extinct by the Middle Cretaceous. Perhaps the Tritylodontids were outcompeted by their relatives, the mammals. Some mammals have developed herbivory during the Late Jurassic

Late Jurassic

The Late Jurassic is the third epoch of the Jurassic Period, and it spans the geologic time from 161.2 ± 4.0 to 145.5 ± 4.0 million years ago , which is preserved in Upper Jurassic strata. In European lithostratigraphy, the name "Malm" indicates rocks of Late Jurassic age...

 and Cretaceous. Or, the Tritylodontids may have gone extinct because of the new plant group, the angiosperms or flowering plants because they weren't used to eating new type of plants. Chronoperates

Chronoperates

Chronoperates paradoxus is a possible therapsid whose remains have been found in Alberta, Canada. It has also been suggested that it may be a symmetrodont.-Sources:http://darrennaish.blogspot.com/2006/05/time-wandering-cynodonts-and-docodonts.html...

may be one exception, it may be a Tritylodontid, and it lived in the Paleocene

Paleocene

The Paleocene or Palaeocene, the "early recent", is a geologic epoch that lasted from about . It is the first epoch of the Palaeogene Period in the modern Cenozoic Era...

, long after the Middle Cretaceous, and after the Cretaceous–Tertiary extinction event. If true, then the Tritylodontids were elusive and rare during the Late Cretaceous

Late Cretaceous

The Late Cretaceous is the younger of two epochs into which the Cretaceous period is divided in the geologic timescale. Rock strata from this epoch form the Upper Cretaceous series...

, because no Tritylodonts were found by that time. However, the Chronoperates 's anatomy almost closely resembles to that of symmetrodont

Symmetrodonta

Symmetrodonta is a basal group of Mesozoic mammals characterized by the triangular aspect of the molars when viewed from above and the absence of a well-developed talonid. The traditional group of symmetrodonts ranges in age from the latest Triassic to the Late Cretaceous. One species,...

s - a mammalian lineage. It is very clear that the Tritylodontids were warm-blooded

Warm-blooded

The term warm-blooded is a colloquial term to describe animal species which have a relatively higher blood temperature, and maintain thermal homeostasis primarily through internal metabolic processes...

. The Tritylodontid fossils were found in the Americas

Americas

The Americas, or America , are lands in the Western hemisphere, also known as the New World. In English, the plural form the Americas is often used to refer to the landmasses of North America and South America with their associated islands and regions, while the singular form America is primarily...

, 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...

, and Eurasia

Eurasia

Eurasia is a continent or supercontinent comprising the traditional continents of Europe and Asia ; covering about 52,990,000 km2 or about 10.6% of the Earth's surface located primarily in the eastern and northern hemispheres...

. They may have managed to live worldwide, including Antarctica.

Genera

• Bienotherium
  Bienotherium
  Bienotherium was a therapsid from the Early Jurassic of China. Despite its size, it is closely related to Lufengia, and is the largest tritylodont from the Lufeng Formation in China....
  
  
• Bienotheroides
• Bocatherium
• Dianzhongia
• Dinnebitodon
  Dinnebitodon
  Dinnebitodon was an advanced herbivorous cynodont of the early Jurassic period. It has only been found in the Kayenta Formation in northeastern Arizona. It closely resembles the related genus Kayentatherium from the same formation...
  
  
• Kayentatherium
  Kayentatherium
  Kayentatherium is a genus of tritylodont, historically referred to as "mammal-like" reptiles. It is one of three tritylodonts from the Kayenta Formation of northern Arizona, United States.-Description:...
  
  
• Lufengia
• Oligokyphus
  Oligokyphus
  Oligokyphus was an advanced herbivorous cynodont of the late Triassic to early Jurassic periods. Originally considered to be an early mammal, it is now classified as a synapsid because Oligokyphus does not have the mammalian jaw attachments and it retains a vestigial joint between the quadrate...
  
  
• Stereognathus
• Tritylodon
  Tritylodon
  Trityldon was a genus of tritylodont, one of the most advanced group of cynodont therapsids. They lived in the Early Jurassic and possibly Late Triassic periods along with dinosaurs. They also shared a lot of characteristics with mammals, and were once considered mammals because of overall...
  
  
• Xenocretosuchus
• Yunnanodon

The Tritylodonts can very much be seen as Mesozoic

Mesozoic

The Mesozoic era is an interval of geological time from about 250 million years ago to about 65 million years ago. It is often referred to as the age of reptiles because reptiles, namely dinosaurs, were the dominant terrestrial and marine vertebrates of the time...

 rodents.

The Tritylodontidae were mammal-like herbivorous cynodont synapsid

Synapsid

Synapsids are a group of animals that includes mammals and everything more closely related to mammals than to other living amniotes. They are easily separated from other amniotes by having an opening low in the skull roof behind each eye, leaving a bony arch beneath each, accounting for their name...

s. They were among the last of the cynodonts, which evolved from the Traversodontidae

Traversodontidae

Traversodontidae is a 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 eastern North America. Traversodonts first appeared in the Middle Triassic, diversified...

 in latest Triassic period, and their lineage survived into the Jurassic period. They were the longest-lived group of the therapsids and along with the Tritheledontidae (Ictidosaurs), the only mammal-like reptiles to endure into the Jurassic period and the only non-mammalian Theropsida (Synapsida) to survive into the late Jurassic period.

Tritylodonts were first discovered in the Upper Triassic rocks of South Africa in the late 1800’s and were initially thought to be amongst the very earliest mammals.

The tritylodont's skull had a high flat crest. They retained the reptilian joint between the quadrate bone of the skull and the auricular bone of the lower jaw, but they were reduced. It is only through the retention of the vestigial reptilian jawbones that they are technically regarded as reptiles. The back of the skull had huge zygomatic arches for the attachment of its large jaw muscle

Muscle

Muscle is a contractile tissue of animals and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to...

s. They also had a very well-developed secondary palate

Secondary palate

The secondary palate is an anatomical structure that divides the nasal cavity from the oral cavity in many vertebrates.In human embryology, it refers to that portion of the hard palate that is formed by the growth of the two palatine shelves medially and their mutual fusion in the midline...

. The tritylodont dentition was very different from that of other cynodonts. They did not have canines

Canine tooth

In mammalian oral anatomy, the canine teeth, also called cuspids, dogteeth, fangs, or eye teeth, are relatively long, pointed teeth...

. The front pair of incisors were enlarged that were very similar to rodents of today. Traversodonts had a large gap, the diastema

Diastema

Diastema may refer to:*Diastema , from the family Gesneriaceae*Diastema , a gap between the front teeth...

, that separated the incisors from the square-shaped cheek. Each of the cheek teeth in the upper jaw had three rows of cusps running along its length that had grooves in between. The lower teeth had two rows of cusps which fitted into the grooves in the upper teeth. The matching of the cusps allowed the teeth to meet in a precise bite. It would grind its food

Food

Food is any substance consumed to provide nutritional support for the body. It is usually of plant or animal origin, and contains essential nutrients, such as carbohydrates, fats, proteins, vitamins, or minerals...

 between the teeth in somewhat the same way that a modern rodent would with their food. The teeth were well suited for shredding plant

Plant

Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...

s matter

Matter

Matter is a general term for the substance of which all physical objects consist. Typically, matter includes atoms and other particles which have mass. A common way of defining matter is as anything that has mass and occupies volume...

.

Tritylodonts were active animals that were probably warm blooded and burrowed like modern day rodents. For example, Oligokyphus

Oligokyphus

Oligokyphus was an advanced herbivorous cynodont of the late Triassic to early Jurassic periods. Originally considered to be an early mammal, it is now classified as a synapsid because Oligokyphus does not have the mammalian jaw attachments and it retains a vestigial joint between the quadrate...

 could be compared to a weasel or mink, with a long, slim body and tail. Its legs had evolved directly beneath the body, as they have in mammals.

See also

• Cynodontia
• 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...
  
  
• Tritheledontidae
• Mammalian embryonic diapause