''Kayentatherium'' is an extinct

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

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, with several mammalian traits including erect limbs, endothermy, and some d ...

cynodont Cynodontia () is a clade of eutheriodont therapsids that first appeared in the Late Permian (approximately 260 Megaannum, mya), and extensively diversified after the Permian–Triassic extinction event. Mammals are cynodonts, as are their extin ...

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� ...

. 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 area of the United States, including northern Arizona, northwest Colorado, Nevada, and Utah. Originally suggested as being Sinemur ...

of northern

Arizona Arizona is a U.S. state, state in the Southwestern United States, Southwestern region of the United States, sharing the Four Corners region of the western United States with Colorado, New Mexico, and Utah. It also borders Nevada to the nort ...

United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...

. ''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 The University of California Museum of Paleontology (UCMP) is a paleontology museum located on the campus of the University of California, Berkeley. The museum is within the Valley Life Sciences Building (VLSB), designed by George W. Kelham ...

in much of the pioneering work on the paleontology of the Kayenta Formation.

History

The first tritylodontid material found within the Kayenta Formation was collected by members of the

United States Geological Survey The United States Geological Survey (USGS), founded as the Geological Survey, is an agency of the U.S. Department of the Interior whose work spans the disciplines of biology, geography, geology, and hydrology. The agency was founded on Mar ...

in 1953. 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 ''Kayentatherium'' is an extinct genus of tritylodontid cynodonts that lived during the Early Jurassic. It is one of two tritylodonts from the Kayenta Formation of northern Arizona, United States. ''Kayentatherium'' means "Kayenta Beast", and is ...

'', 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

perinate A perinate refers to a member of a viviparous species from approximately one month before birth to one month after it. The term is derived from the Latin root ''perinatus'', meaning "around birth." In medical and biological contexts, it specificall ...

s, 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 Tritylodontidae Early Jurassic synapsids of North America Kayenta Formation Fossil taxa described in 1982

History

Description

Reproduction

See also

References