Redonda Formation

Redonda Formation
Stratigraphic range: Norian ~221–206 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Type	Formation
Unit of	Chinle Group
Sub-units	Duke Ranch, Quay, Red Peak, San Jon Creek & Wallace Ranch members
Underlies	Entrada Formation
Overlies	Bull Canyon Formation
Thickness	25–425 feet (7.6–129.5 m)
Lithology
Primary	Shale
Other	Limestone, sandstone
Location
Coordinates	34°57′54″N 103°42′04″W / 34.965°N 103.701°W / 34.965; -103.701
Approximate paleocoordinates	9°54′N 43°12′W / 9.9°N 43.2°W / 9.9; -43.2
Region	New Mexico
Country	United States
Type section
Named for	Redonda Mesa
Named by	Dobrovolny and Summerson
Year defined	1946
Redonda Formation (the United States) Show map of the United States Redonda Formation (New Mexico) Show map of New Mexico

The Redonda Formation is a geologic formation exposed in eastern New Mexico.^[1] It contains vertebrate fossils of the late Triassic Period.^[2] Fossil theropod tracks have been reported from the formation.^[3]

The formation consists of interbedded fine-grained red-brown sandstone and mudstone. It conformably overlies the Bull Canyon Formation^[4] and underlies the Entrada Formation.^[2]

The formation is interpreted as having been deposited in a lake with an area of about 5,000 square kilometres (1,900 sq mi).^[4]

The formation has few fossil plants, with only Neocalamites reported, but it contains abundant invertebrate fossils (conchostracans and ostracods) and a diverse assemblage of vertebrate fossils.^[4][3]

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fish of the Redonda Formation
Taxa	Presence	Notes	Images
Cionichthys	Skull fragments	A redfieldiid
Ceratodus		A lungfish
Coelacanthidae indet.	Fragmentary material	Possibly assignable to Chinlea or Quayia
Hemicalypterus	scales	A dapediid
Semionotus	Abundant, found in large deathbeds	A semionotid
Synornichthys	Skull fragments	A redfieldiid

Stereospondyls of the Redonda Formation
Taxa	Presence	Notes	Images
Apachesaurus	Numerous specimens	A metoposaurid, possibly juveniles of Koskinodon

Archosauriforms of the Redonda Formation
Taxa	Presence	Notes	Images
Apachesuchus	Osteoderms	An aetosaur similar to Neoaetosauroides
Redondasaurus	Numerous skulls and other skeletal remains	A phytosaur
Redondasuchus	Osteoderms and other fragments	A typothoracisine aetosaur related to Typothorax
Redondavenator	Snout bones and a scapulocoracoid	A large, predatory basal crocodylomorph
Vancleavea	Osteoderms	An unusual non-archosaurian archosauriform

The unit was first named as the Redonda Member of the Chinle Formation by Dobrovolny and Summerson in 1947.^[1] Griggs and Read raised the unit to formation rank in 1959, and also assigned an age of late Triassic based on the presence of tracks of a bipedal dinosaur and of a phytosaur skull.^[2]

• List of dinosaur-bearing rock formations
  • List of stratigraphic units with theropod tracks

• Dobrovolny, Ernest; Summerson, C.H. (1947). "Geology of northwestern Quay County, New Mexico". U.S. Geological Survey Oila Nd Gas Investigations Map. OM-62. doi:10.3133/om62.
• Griggs, R.L.; Read, C.B. (1959). "Revisions in Stratigraphic Nomenclature in Tucumcari-Sabinoso Area, Northeastern New Mexico: GEOLOGICAL NOTES". AAPG Bulletin. 43 (8): 2003–2007. doi:10.1306/0BDA5E8E-16BD-11D7-8645000102C1865D.
• Lucas, S.G.; Hunt, A.P. (1989). "Revised Triassic stratigraphy in the Tucumcari basin, east-central New Mexico". In Lucas, S.G.; Hunt, A.P. (eds.). Dawn of the age of dinosaurs in the American southwest. New Mexico Museum of Natural History and Science. pp. 150–170. Retrieved 17 September 2020.
• Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. 861 pp. ISBN 0-520-24209-2.