# Redonda Formation

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Geologic formation exposed in eastern New Mexico

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](/source/Formation_(geology)) exposed in eastern [New Mexico](/source/New_Mexico).[1] It contains vertebrate [fossils](/source/Fossil) of the [late Triassic](/source/Late_Triassic) [Period](/source/Period_(geology)).[2] Fossil [theropod](/source/Theropod) tracks have been reported from the formation.[3]

## Description

The formation consists of interbedded fine-grained red-brown [sandstone](/source/Sandstone) and [mudstone](/source/Mudstone). It conformably overlies the [Bull Canyon Formation](/source/Bull_Canyon_Formation)[4] and underlies the [Entrada Formation](/source/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]

## Fossils

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

### Vertebrate fauna

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#### Fish

fish of the Redonda Formation Taxa Presence Notes Images Cionichthys Skull fragments A redfieldiid 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 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 Redondasaurus 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](/source/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](/source/Phytosaur) skull.[2]

## See also

- [List of dinosaur-bearing rock formations](/source/List_of_dinosaur-bearing_rock_formations) - [List of stratigraphic units with theropod tracks](/source/List_of_stratigraphic_units_with_theropod_tracks)

## References

1. ^ [***a***](#cite_ref-dobrolvny-summerson-1947_1-0) [***b***](#cite_ref-dobrolvny-summerson-1947_1-1) Dobrovolny and Summerson 1947

1. ^ [***a***](#cite_ref-griggs-read-1959_2-0) [***b***](#cite_ref-griggs-read-1959_2-1) [***c***](#cite_ref-griggs-read-1959_2-2) Griggs and Read 1959

1. ^ [***a***](#cite_ref-dinosaurdistribution_3-0) [***b***](#cite_ref-dinosaurdistribution_3-1) Weishampel, et al. (2004). "Dinosaur distribution." Pp. 517-607.

1. ^ [***a***](#cite_ref-lucas-hunt-1989_4-0) [***b***](#cite_ref-lucas-hunt-1989_4-1) [***c***](#cite_ref-lucas-hunt-1989_4-2) Lucas and Hunt 1989

### Bibliography

- Dobrovolny, Ernest; Summerson, C.H. (1947). "Geology of northwestern Quay County, New Mexico". *U.S. Geological Survey Oila Nd Gas Investigations Map*. OM-62: 2. [Bibcode](/source/Bibcode_(identifier)):[1947usgs.rept....2D](https://ui.adsabs.harvard.edu/abs/1947usgs.rept....2D). [doi](/source/Doi_(identifier)):[10.3133/om62](https://doi.org/10.3133%2Fom62).

- 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](/source/Doi_(identifier)):[10.1306/0BDA5E8E-16BD-11D7-8645000102C1865D](https://doi.org/10.1306%2F0BDA5E8E-16BD-11D7-8645000102C1865D).

- Lucas, S.G.; Hunt, A.P. (1989). ["Revised Triassic stratigraphy in the Tucumcari basin, east-central New Mexico"](https://books.google.com/books?id=Ar1hCgAAQBAJ&dq=Revised+Triassic+stratigraphy+in+the+Tucumcari+basin%2C+east+central+New+Mexico&pg=PA150). 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](/source/ISBN_(identifier)) [0-520-24209-2](https://en.wikipedia.org/wiki/Special:BookSources/0-520-24209-2).

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