Doswellia

Doswellia is an extinct genus of archosauriform reptile from the Late Triassic of North America. It is the namesake of the family Doswelliidae, related to the proterochampsids which were more common in South America. Doswellia was a low and heavily built carnivore which lived during the Late Triassic. It possesses many unusual features, including a wide, flattened head with narrow jaws and a box-like rib cage covered by at least ten rows of bony plates.

The type species, Doswellia kaltenbachi, was named in 1980 from fossils found within the Vinita member of the Doswell Formation (formerly known as the Falling Creek Formation) in Virginia. The formation, which is found in the Taylorsville Basin, is part of the larger Newark Supergroup. Doswellia is named after Doswell, the town from which much of the taxon's remains have been found.

A supposed second species, D. sixmilensis, was described in 2012 from the Bluewater Creek Formation of the Chinle Group in New Mexico; however, this species was subsequently recognized as a separate doswelliid genus, Rugarhynchos. Bonafide Doswellia kaltenbachi fossils are also known from the Chinle Formation in Arizona.

The most complete specimens of Doswellia were discovered in 1974 during the construction of a sewage treatment plant in Doswell, Virginia. A party from the Smithsonian, led by James Kaltenbach (the namesake of Doswellia kaltenbachi), unearthed a large block containing a partial skeleton, including numerous vertebrae, ribs, osteoderms (bony plates), and other bones. This block, USNM 244214, has been designated the holotype of D. kaltenbachi.

Two additional slabs were later unearthed at the same site and almost certainly pertained to the same individual. One of these slabs contained additional vertebrae and ribs while the other contained a partial skull and mandible. These additional slabs were collectively termed the paratype, USNM 214823. An isolated right jugal found at the site (USNM 437574) was also referred to the species.

In the 1950s and 1960s, several additional bones (including vertebrae, osteoderms, a dentary, and a femur) were unearthed near Ashland, a little south of Doswell. These specimens were initially believed to have belonged to phytosaurs, but were recognized as pertaining to Doswellia after the Doswell specimens were found. The Ashland specimens are cataloged as USNM 186989 and USNM 244215.

Assorted osteoderms and vertebrae have been assigned to Doswellia from areas further west: the Colorado City Formation in Texas and the Monitor Butte Formation in Utah. Fossils referable to Doswellia cf. kaltenbachi are known from Petrified Forest National Park in Arizona. They were found in the Blue Mesa Member of the Chinle Formation, making the Arizona remains among the youngest in the genus.

In 2012, a new species of archosauriform was described and referred to Doswellia, as the second species Doswellia sixmilensis. The holotype of this species was NMMNH P-61909, an incomplete skeleton including skull fragments, osteoderms, vertebrae, and possible limb fragments. It was found in strata of the Bluewater Creek Formation exposed at Sixmile Canyon in McKinley County, New Mexico. A 2020 redescription of "Doswellia" sixmilensis recognized that its supposed snout fragments actually represented an entire skull with unique traits different from Doswellia. Once these major anatomical differences were discovered, the species was given its own doswelliid genus, Rugarhynchos.