''Kayentatherium'' is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

tritylodontid Tritylodontidae ("three-knob teeth", named after the shape of their cheek teeth) is an extinct family of small to medium-sized, highly specialized mammal-like cynodonts, bearing several mammalian traits like erect limbs, endothermy and details ...

cynodont The cynodonts () (clade Cynodontia) are a clade of eutheriodont therapsids that first appeared in the Late Permian (approximately 260 mya), and extensively diversified after the Permian–Triassic extinction event. Cynodonts had a wide varie ...

s that lived during the

Early Jurassic The Early Jurassic Epoch (geology), Epoch (in chronostratigraphy corresponding to the Lower Jurassic series (stratigraphy), Series) is the earliest of three epochs of the Jurassic Period. The Early Jurassic starts immediately after the Triassic-J ...

. It is one of two tritylodonts from the

Kayenta Formation The Kayenta Formation is a geological formation in the Glen Canyon Group that is spread across the Colorado Plateau province of the United States, including northern Arizona, northwest Colorado, Nevada, and Utah. Traditionally has been suggested ...

of northern

Arizona Arizona ( ; nv, Hoozdo Hahoodzo ; ood, Alĭ ṣonak ) is a state in the Southwestern United States. It is the 6th largest and the 14th most populous of the 50 states. Its capital and largest city is Phoenix. Arizona is part of the Fou ...

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...

. ''Kayentatherium'' means "Kayenta Beast", and is named for the geological formation in which it was found, the

. ''Kayentatherium'' is known from several specimens.Kermack, D. 1982. A new tritylodont from the Kayenta Formation of Arizona. Zoological Journal of the Linnean Society, 76. 1-17.Sues, Hans-Dieter & F. A. Jenkins. 2006. The Postcranial Skeleton of Kayentatherium Wellesi from the Lower Jurassic Kayenta Formation of Arizona and the Phylogenetic Significance of Postcranial Features in Tritylodontid Cynodonts in: Carrano, Matthew T., Gaudin, T. J., Blob, R. W. and Wible, J. R., Amniote Paleobiology: Perspectives on the Evolution of Mammals, Birds, and Reptiles: The University of Chicago Press. pp. 114-152. The specific name honors paleontologist Samuel Welles, who worked with the University of California Museum of Paleontology in much of the pioneering work on the paleontology of the Kayenta Formation.

History

The first tritylodontid material found in the Kayenta Formation were collected in the 1950s, and further material was collected in 1977 and 1982 by a team led by Farish Jenkins. Also found in the same rocks were '' Dinnebitodon amarali'' and '' Nearctylodon broomi'', but the latter was later considered to be a juvenile specimen of ''Kayentatherium'', and so was synonymised.

Description

It was about a meter long, the skull was over in length. It was a robust and stocky animal with a large head and stout backbone. Some researchers think it might have been semi-aquatic, with adaptations formerly thought to indicate digging habits now interpreted as specialisation towards limb-powered swimming. Slight flattening and flaring of the tail vertebrae also suggest specialisms for a semi-aquatic ecology.Hoffman E, and Rowe TB. 2017 Postcranial anatomy of ''Kayentatherium wellesi'': swimming adaptations in a mammaliamorph from the Early Jurassic. Abstract from the Society of Vertebrate Paleontology Annual Conference. If this was the case, it would be one of the earliest examples of semi-aquatic specialism in mammaliamorphs in the mammal fossil record.

Reproduction

A find in 2000 of ''Kayentatherium wellesi'' from the Kayenta formation of Arizona was examined by microCT scan, and revealed an adult with at least 38 perinates, a number considerably higher than any living mammal litter. The size of the group suggests a clutch of eggs. Perinates had similar skull proportions to adults, with well-developed teeth, and may have been able to fend for themselves at birth. Allometric study shows that tritylodontids had proportionally smaller brains at this stage than mammal perinates, which supports the hypothesis that the evolution of larger brain size in early mammals was associated with changes in reproductive strategy to invest more parental energy in a smaller number of offspring.Eva A. Hoffman; Timothy B. Rowe (2018). "Jurassic stem-mammal perinates and the origin of mammalian reproduction and growth". Nature. 561 (7721): 104–108. doi:10.1038/s41586-018-0441-3. .

References

{{Taxonbar, from=Q6380561 Prehistoric cynodont genera Jurassic synapsids Mesozoic synapsids of North America Fossil taxa described in 1982 Kayenta Formation Tritylodontids

History

Description

Reproduction

See also

References