Doswellia
Doswellia is an extinct genus of archosauriform from the Late Triassic of North America. It belongs to the family Doswelliidae, which also includes the genera Archeopelta and Tarjadia from South America. Doswellia was a terrestrial carnivore that reached a length of 2 m (7 ft) and lived during the Carnian stage of the Late Triassic.[1][2] It possesses many unusual features including a wide, flattened head with narrow jaws and a box-like rib cage surrounded by many rows of bony plates. The type species Doswellia kaltenbachi was named in 1980 from fossils found within the Poor Farm Member of 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 remains have been found. A second species called D. sixmilensis was described in 2012 from the Bluewater Creek Formation of the Chinle Group in New Mexico.[3]
Description
Doswellia possesses many highly derived features in its skeleton. The skull is low and elongated with a narrow snout and wide temporal region behind the eye sockets. The temporal region is unusual in that it is euryapsid, which means that the lower of the two temporal holes on either side of the skull has closed. The jugal bone has expanded into the region the lower temporal opening would normally occupy. Paired squamosal bones extend beyond the skull's back margin to form small horn-like projections. The skull of Doswellia lacks several bones found in other archosauriforms, including the postfrontals, tabulars, and postparietals.[4]
The body of Doswellia is also distinctive. The neck is elongated and partially covered by a fused collection of bony scutes called a nuchal plate. The ribs in the front part of the torso project horizontally from the spine and then bend at nearly 90-degree angles to give the body of Doswellia a box-like shape. The blade-like ilium bone of the hip also projects horizontally. The back and underside are covered with ordered rows of bony plates called osteoderms.[4]
Taxonomy
The type species, Doswellia kaltenbachi, was described by Weems in 1980.[5] Weems placed Doswellia within Thecodontia, a group of archosaurs that traditionally included many Triassic archosaurs. He placed the genus within its own family, Doswelliidae, and suborder, Dosweliina. Parrish (1993) placed Doswellia among the most primitive of the crurotarsans, a group that includes crocodilians and their extinct relatives. More recently, Dilkes and Sues (2009) proposed a close relationship between Doswellia and the early archosauriform family Proterochampsidae. Desojo et al. (2011) added the Brazilian archosauriforms Tarjadia and Archeopelta to Doswelliidae, and found support for Dilkes and Sues' classification in their own phylogenetic analysis.[6]
References
- ↑ PaleoBiology Database: Doswellia, basic info
- ↑ http://palaeos.com/vertebrates/archosauria/derived_rauisuchia.html
- ↑ Heckert, Andrew B.; Lucas, Spencer G.; Spielmann, Justin A. (2012). "A new species of the enigmatic archosauromorph Doswellia from the Upper Triassic Bluewater Creek Formation, New Mexico, USA". Palaeontology. 55 (6): 1333–1348. doi:10.1111/j.1475-4983.2012.01200.x.
- 1 2 Dilkes, D.; Sues, H. D. (2009). "Redescription and phylogenetic relationships of Doswellia kaltenbachi (Diapsida: Archosauriformes) from the Upper Triassic of Virginia". Journal of Vertebrate Paleontology. 29: 58. doi:10.1080/02724634.2009.10010362.
- ↑ R. E. Weems (1980). "An unusual newly discovered archosaur from the Upper Triassic of Virginia, U.S.A.". Transactions of the American Philosophical Society, New Series. 70 (7): 1–53. doi:10.2307/1006472.
- ↑ Julia B. Desojo, Martin D. Ezcurra and Cesar L. Schultz (2011). "An unusual new archosauriform from the Middle–Late Triassic of southern Brazil and the monophyly of Doswelliidae". Zoological Journal of the Linnean Society. 161 (4): 839–871. doi:10.1111/j.1096-3642.2010.00655.x.
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