Redonda Formation

Redonda Formation
Stratigraphic range: Norian ~
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
Approximate paleocoordinates
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) Redonda Formation (New Mexico)

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

Description

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

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

Fossils

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.

Vertebrate fauna

Fish

fish of the Redonda Formation
Taxa	Presence	Notes	Images
Cionichthys	Skull fragments	A redfieldiid	Error creating thumbnail: Semionotus
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

Stereospondyls of the Redonda Formation
Taxa	Presence	Notes	Images
Apachesaurus	Numerous specimens	A metoposaurid, possibly juveniles of Koskinonodon	File:Apachesaurus1DB.jpg Apachesaurus

Synapsids

Synapsids of the Redonda Formation
Taxa	Presence	Notes	Images
Redondagnathus	teeth	A trirachodontid cynodont

Archosauriforms

Archosauriforms of the Redonda Formation
Taxa	Presence	Notes	Images
Apachesuchus	Osteoderms	An aetosaur similar to Neoaetosauroides	File:Redondasaurus bermani at CMNH 04.jpg Redondasaurus File:Vancleavea.jpg Vancleavea
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

History of investigation

The unit was first named as the Redonda Member of the Chinle Formation by Dobrovolny and Summerson in 1947. 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.

See also

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

References

Bibliography

• Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. 861 pp. .