Redonda Formation facts for kids

Quick facts for kids Redonda Formation Stratigraphic range: Norian ~221–206Ma PreЄ Є 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

The Redonda Formation is a special layer of rock found in eastern New Mexico. It's like a giant history book made of stone! This rock layer holds amazing fossils of ancient animals that lived during the late Triassic Period. Scientists have even found tracks of theropod dinosaurs here.

What is the Redonda Formation?

The Redonda Formation is made mostly of fine-grained, reddish-brown sandstone and mudstone. Think of it like hardened mud and sand from a very old lake. This rock layer sits on top of another rock layer called the Bull Canyon Formation. It is also found below the Entrada Formation.

Scientists believe the Redonda Formation was once the bottom of a huge ancient lake. This lake was about 5,000 square kilometers (about 1,900 square miles) in size!

What Fossils are Found in the Redonda Formation?

The Redonda Formation doesn't have many plant fossils. Only one type of ancient plant, Neocalamites, has been found. But it's full of tiny invertebrate fossils, like conchostracans and ostracods. Most excitingly, it has many different kinds of vertebrate fossils, which are animals with backbones!

Ancient Fish of the Redonda Formation

Many different kinds of fish fossils have been found in the Redonda Formation. Some of these fish were quite common.

Fish of the Redonda Formation
Taxa	What was found?	Interesting Facts	Images
Cionichthys	Skull pieces	This fish was a type called a redfieldiid.	Semionotus
Ceratodus		This was an ancient lungfish.
Coelacanthidae indet.	Small pieces	These might be related to Chinlea or Quayia.
Hemicalypterus	Scales	This fish was a dapediid.
Semionotus	Many fossils, found in large groups	This fish was very common in the ancient lake.
Synornichthys	Skull pieces	Another type of redfieldiid fish.

Stereospondyls: Ancient Amphibians

Stereospondyls were a group of ancient amphibians, like giant salamanders.

Stereospondyls of the Redonda Formation
Taxa	What was found?	Interesting Facts	Images
Apachesaurus	Many different fossils	This was a metoposaurid. It might have been the young version of another amphibian called Koskinodon.	Apachesaurus

Synapsids: Early Mammal Relatives

Synapsids were a group of animals that eventually led to mammals.

Archosauriforms: Crocodile and Dinosaur Relatives

Archosauriforms were a diverse group that included the ancestors of crocodiles and dinosaurs.

Archosauriforms of the Redonda Formation
Taxa	What was found?	Interesting Facts	Images
Apachesuchus	Osteoderms (bony plates in the skin)	This was an aetosaur, similar to Neoaetosauroides.	Redondasaurus Vancleavea
Redondasaurus	Many skulls and other bones	This was a phytosaur, a crocodile-like reptile.
Redondasuchus	Osteoderms and other bone pieces	Another type of aetosaur, related to Typothorax.
Redondavenator	Snout bones and shoulder bone	This was a large, meat-eating crocodylomorph, an early relative of crocodiles.
Vancleavea	Osteoderms	A very unusual archosauriform, not quite an archosaur.

How Was the Redonda Formation Discovered?

The Redonda Formation was first named in 1947 by scientists Dobrovolny and Summerson. At that time, they called it the Redonda Member of the Chinle Formation.

Later, in 1959, other scientists named Griggs and Read decided it was important enough to be called its own "formation." They also figured out that it was from the late Triassic Period. They knew this because they found tracks of a two-legged dinosaur and a phytosaur skull in the rock.