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Redonda Formation
Stratigraphic range: Norian
~221–206Ma
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; -103.701Coordinates: 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

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
Semionotus model
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 Koskinodon

Apachesaurus1DB
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 bermani at CMNH 04
Redondasaurus
Vancleavea
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.

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