Redonda Formation
Geologic formation exposed in eastern New Mexico
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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]
| 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 | 34.965°N 103.701°W |
| Approximate paleocoordinates | 9.9°N 43.2°W |
| 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) | |
Description
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]
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.[4][3]
Vertebrate fauna
Fish
| fish of the Redonda Formation | ||||
|---|---|---|---|---|
| Taxa | Presence | Notes | Images | |
| Skull fragments | A redfieldiid |
 | ||
| A lungfish | ||||
|
Coelacanthidae indet. |
Fragmentary material | Possibly assignable to Chinlea or Quayia | ||
| scales | A dapediid | |||
| Abundant, found in large deathbeds | A semionotid | |||
|
Synornichthys |
Skull fragments | A redfieldiid | ||
Stereospondyls
| Stereospondyls of the Redonda Formation | ||||
|---|---|---|---|---|
| Taxa | Presence | Notes | Images | |
| Numerous specimens |
A metoposaurid, possibly juveniles of Koskinonodon |
 | ||
Synapsids
| Synapsids of the Redonda Formation | ||||
|---|---|---|---|---|
| Taxa | Presence | Notes | Images | |
|
Redondagnathus |
teeth | |||
Archosauriforms
| Archosauriforms of the Redonda Formation | ||||
|---|---|---|---|---|
| Taxa | Presence | Notes | Images | |
| Osteoderms |
An aetosaur similar to Neoaetosauroides |
  | ||
| Numerous skulls and other skeletal remains | ||||
| Osteoderms and other fragments |
A typothoracisine aetosaur related to Typothorax | |||
| Snout bones and a scapulocoracoid |
A large, predatory basal crocodylomorph | |||
| 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.[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]