Oligokyphus was an advanced herbivorous

Herbivore

Herbivores are organisms that are anatomically and physiologically adapted to eat plant-based foods. Herbivory is a form of consumption in which an organism principally eats autotrophs such as plants, algae and photosynthesizing bacteria. More generally, organisms that feed on autotrophs in...

 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...

 of the 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 early 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...

 periods. Originally considered to be an early 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...

, it is now classified as a 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...

 because Oligokyphus does not have the mammalian jaw attachments and it retains a vestigial joint between the quadrate bone and the squamosal

Squamosal

The squamosal is a bone of the head of higher vertebrates. It is the principal component of the cheek region in the skull, lying below the temporal series and otic notch and bounded anteriorly by postorbital. Posteriorly, the squamosal articulates with the posterior elements of the palatal complex,...

 bone in the skull.

Description

Oligokyphus (meaning "small curved animal"), was a small animal, around 50 centimetres (19.7 in) in length, belonging to the herbivorous Tritylodontidae

Tritylodontidae

Tritylodontids were small to medium-sized, highly specialized and extremely mammal-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-like cynodont...

 family. It resembled a weasel in appearance, with a long and slim body. The limbs sat directly under the body, like modern mammals, but unlike other known synapsids.

Oligokyphus was found widely across North America, Europe and China. This indicates that there were substitutes with the terrestrial vertebrates.

Skull and jaw

The teeth of the upper and lower jaw contain bump rows that fit together perfectly in order to maintain an accurate bite. Oligokyphus had a face similar to that of modern mammals, although there were differences in the cheekbones and eyesockets. It had a bony secondary palate

Palate

The palate is the roof of the mouth in humans and other mammals. It separates the oral cavity from the nasal cavity. A similar structure is found in crocodilians, but, in most other tetrapods, the oral and nasal cavities are not truly separate. The palate is divided into two parts, the anterior...

 and double-rooted cheek teeth. Unlike mammals, the teeth of Oligokyphus did not occlude. The jaw was double jointed, and the neck was flexible, with an atlas

Atlas (anatomy)

In anatomy, the atlas is the most superior cervical vertebra of the spine.It is named for the Atlas of Greek mythology, because it supports the globe of the head....

 and axis

Axis (anatomy)

In anatomy, the second cervical vertebra of the spine is named the axis or epistropheus.It forms the pivot upon which the first cervical vertebra , which carries the head, rotates....

 and a double occipital condyle

Occipital condyle

The occipital condyles are undersurface facets of the occipital bone in vertebrates, which function in articulation with the superior facets of the atlas vertebra....

.

The teeth were different from those of related cynodonts; there were no canine teeth, and unusually large, rodent-like incisor

Incisor

Incisors are the first kind of tooth in heterodont mammals. They are located in the premaxilla above and mandible below.-Function:...

s. There is a large gap, or diastema

Diastema

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

, separating the cheek teeth from the incisors. The lower jaw of these animals moved back and forth when the mouth was shut so that the food could be chopped up. Oligokyphus had no premaxilla

Premaxilla

The incisive bone is the portion of the maxilla adjacent to the incisors. It is a pair of small cranial bones at the very tip of the jaws of many animals, usually bearing teeth, but not always. They are connected to the maxilla and the nasals....

, but did have a lateral extension of 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...

.

While the postcanines in non-mammalians, such as Oligokyphus, are difficult to differentiate from canines, the lower postcanines of Oligokyphus (also considered to be pre-molars) are defining from other Tritylodonts. On lower postcanine teeth of Trityldonts, two cusps can be found per row; however, Oligokyphus have two rows with three cusps in each row. The upper postcanines have also been found in fossil records to be longer than they are wide. These cusps, specific to Oligokyhpus Tritylodonts, allowed for a well-fitting bite that was particularly good at shredding plant material dense in fiber. The foremost incisors are similar to those of today's rodents, extremely intensified and enlarged.. The typical location of canine teeth is left empty with Oligokyphus. Instead, a gap is inserted in this area of the jaw as Oligokyphus lack the teeth commonly known as canines.

Cladistics

Oligokyphus is in the family Trityledontidae. The family is named after the shape of their teeth. Trityledontidae means "three knob teeth". The members of the family were all small to medium sized advanced synapsids with combined specialized structures for herbivorous eating. They were the last members of the non-mammalian synapsids. The first Trityledont was found in South Africa in the upper Jurassic rocks. It was first thought to be on of the earliest mammals. This classification has since been adjusted. These non-mammals became progressively more mammal-like. They are now classified as the closest relatives to the mammals and this is supported by their high, flat crested jaw, large zygomatic arch

Zygomatic arch

The zygomatic arch or cheek bone is formed by the zygomatic process of temporal bone and the temporal process of the zygomatic bone , the two being united by an oblique suture; the tendon of the Temporalis passes medial to the arch to gain insertion into the coronoid process...

es, well developed secondary palate, and dentition.

There have also been comparisons between the cranial nerves of Trityledonts and mammals. The shoulder girdle and forelimb structures were suggestive of these animals digging. These animals are extremely active and burrow in leaf litter and dirt, which suggests characteristics of rodents and rabbits. They naturally have a metabolism that is partially or completely endothermic. They were thought to be driven out by relatives such as mammals, which were competitors for the same territory. Another reason that this animal could have gone extinct is due to new plant development. Some flowering plants, or angiosperms, can be detrimental to these animals since they may not be used to eating new plants.

Oligokyphus is placed into the subgroup Probainognathia. This forms a monophyletic group with the tritheledontid Pachygenelus.

Fossil finds

Though Oligokyphus is very widespread, it was not until 1953 that representatives of this group were found. Information was first collected from the Kayenta Formation on Comb Ridge in northeastern Arizona. Numerous specimens of Oligokyphus were obtained by Harvard University and the Museum of Northern Arizona in the "Silty Facies". Many fossils have also been found throughout the UK, Germany and China. Some very small fragment remains have also been found in Antarctica. By these fossil records, one can see that Oligokyphus have a vertical humerus and a minor trochanter.
This broad distribution indicates that there were no barriers to separate this terrestrial vertebrate.

Habitat

Oligokyphus were small tetrapod, terrestrial animals. They have long been considered as mammaliomorphs, a link between reptiles and mammals. It is believed these animals were primarily land dwelling, living amongst small shrubs or bushes. It is also thought that Oligokyphus fed on seeds or nuts, as their teeth resemble those of modern animals that also feed on seeds and nuts. It is a rather difficult to estimate the social behaviors of Oligokyphus as most of it does not preserve in the fossil record. However, considering the conditions on the planet during the times that Oligokyphus was alive and thriving (late Triassic and early Jurassic) and also the locations of which fossils of these animals were found, some educated predictions can be made about their metabolism and feeding habits. Oligokyphus, with its conveniently placed leg and hip structures, likely was quick-moving and fed off of low-lying plant life. With its long weasel-like body, it may have even been possible for Oligokyphus to reach higher vegetation simply by standing on its hind legs. It probably had good use of its hands to manipulate seeds and other digestively pleasing foods. There has not been any support showing Oligokyphus had the ability to climb vertically, as some rodents are capable of doing today.

Parental care

This illustration shows that there is a good possibility that Oligokyphus had parental care. This is assumed to be true because of the transitional state Oligokyphus was in from reptiles to mammalian. Today most mammals and some reptiles show parental care to their young. This makes a good argument to the possibility of parental care with Oligokyphus, but with all prehistoric creatures it is not a 100% assumption without actually seeing them interact.