Cedar Mountain Formation facts for kids

Quick facts for kids Cedar Mountain Formation Stratigraphic range: Late Berriasian-Cenomanian ~140–95Ma PreЄ Є O S D C P T J K Pg N
Type	Geological formation
Unit of	Dakota Group
Sub-units	See text
Underlies	Naturita Formation
Overlies	Morrison Formation
Thickness	Varies, some sections over 1000 metres
Lithology
Primary	Conglomerate, sandstone, mudstone
Location
Coordinates	39°15′00″N 110°49′05″W / 39.250°N 110.818°W / 39.250; -110.818
Approximate paleocoordinates	40°12′N 69°00′W / 40.2°N 69.0°W / 40.2; -69.0
Region	Utah
Country	United States
Type section
Named for	Cedar Mountain
Named by	Stokes
Year defined	1944

The Cedar Mountain Formation is a special type of rock layer found in eastern Utah. It's named after Cedar Mountain, where it was first studied in 1944 by William Lee Stokes. This formation is important because it holds many fossils, especially dinosaurs, from a time long ago.

What is the Cedar Mountain Formation?

The drab-colored lower part of the Cedar Mountain Formation, sitting on top of the brighter Morrison Formation.

This rock formation is made of sediments that were laid down on land, not in the ocean. Imagine ancient rivers, lakes, and floodplains – that's where these rocks formed! Scientists believe the Cedar Mountain Formation was created during the last half of the Early Cretaceous period, about 127 to 98 million years ago. We know this thanks to radiometric dating, which is a way to figure out the age of rocks using natural radioactivity.

The Cedar Mountain Formation sits between two other rock layers: the Morrison Formation below it and the Naturita Formation above it.

Layers of the Formation

This chart shows the different layers (members) that make up the Cedar Mountain Formation and how old they are. Some layers might be missing because they were never deposited or were worn away later.

The Cedar Mountain Formation is made up of several smaller layers, called "members." Scientists sometimes disagree on whether there are four or five members. Most agree that the Buckhorn Conglomerate is the very bottom layer. Above it are the Yellow Cat Member, Poison Strip Sandstone, Ruby Ranch Member, and the Mussentuchit Member. Each of these layers tells us something different about the ancient environment.

Buckhorn Conglomerate

This is the lowest layer of the Cedar Mountain Formation. It's named after the Buckhorn Reservoir. It's made of conglomerate, which is rock made of rounded pebbles and stones cemented together.

Yellow Cat Member

This layer is named after the Yellow Cat mining area, near Arches National Park. It's mostly made of dull gray mudstones, which are rocks formed from ancient mud. These mudstones show signs of old soils, meaning the area was once a floodplain with rivers. This layer is thought to be about 140 to 133 million years old.

Poison Strip Sandstone

Named for the Poison Strip uranium area, this layer has prominent sandstone cliffs. It formed from ancient river channels, with some mud and limestone from floodplains and small ponds. This layer is famous for "Tony's Bone Bed."

• Tony's Bone Bed: This is a very important spot where many dinosaur bones were found in 1998. The bones were not connected, and some looked like they had been trampled or chewed by scavengers. This suggests the bones gathered slowly over time, perhaps during dry seasons when river water was low.

Ruby Ranch Member

This is the most widespread and easy-to-spot layer of the Cedar Mountain Formation. It's named after the Ruby Ranch. It's mostly maroon-colored mudstones with round, hard lumps called carbonate nodules. These nodules formed in ancient soils during a time when the climate was dry with strong seasons. The rivers in this period flowed northeast, towards an ancient sea.

Mussentuchit Member

This is the top layer of the Cedar Mountain Formation, named after Mussentuchit Wash. It's mostly gray mudstones with lots of fossilized plant material and volcanic ash. This suggests it was a wet coastal plain with plenty of rain. This layer is about 104 to 98 million years old.

Fossils Found Here

The Cedar Mountain Formation is a treasure chest of Early Cretaceous fossils, especially dinosaurs! Scientists have only really started studying these fossils since the 1990s. The discoveries here are helping us understand how dinosaurs changed over time and how the North American continent moved.

Dinosaurs

Example of dinosaurs from the Cedar Mountain Formation include the armored Gastonia (top left), the fierce Utahraptor (top right), a large meat-eating dinosaur tooth (bottom left), and the plant-eating Tenontosaurus (bottom right).

Scientists have found at least two, and possibly three, different groups of dinosaurs in the Cedar Mountain Formation.

The older dinosaurs, found in the Yellow Cat, Poison Strip, and lower Ruby Ranch layers, include dinosaurs like Nedcolbertia (a small meat-eater) and Cedarosaurus (a long-necked plant-eater). Other dinosaurs like the armored Gastonia and an unnamed iguanodontid are similar to dinosaurs found in England from the same time. This tells us that North America and Europe were still connected back then.

However, the younger dinosaurs, found in the upper Ruby Ranch and Mussentuchit layers, are more like dinosaurs found in Asia! For example, the armored Cedarpelta is related to dinosaurs from Mongolia. This shows that as the North American continent drifted westward, it eventually connected with Asia, bringing new types of dinosaurs. This upper group also includes early tyrannosaurs, ceratopsians (horned dinosaurs), and pachycephalosaurs (dome-headed dinosaurs).

Armored Dinosaurs (Ankylosaurs)

Armored Dinosaurs from the Cedar Mountain Formation
Genus	Species	Member	What was found	Notes	Images
Animantarx	Animantarx ramaljonesi	Mussentuchit Member	Part of a skull and skeleton.		Gastonia burgei Sauropelta
Cedarpelta	Cedarpelta bilbeyhallorum	Mussentuchit Member	Skull and body bones.
Gastonia	Gastonia burgei	Upper Yellow Cat Member	Two skulls, two partial skulls, and four or five partial skeletons.
	G. lorriemcwhinneyae	Ruby Ranch Member
Peloroplites	Peloroplites cedrimontanus	Mussentuchit Member
Sauropelta	Indeterminate	Ruby Ranch Member

Beaked Dinosaurs (Neornithischians)

Beaked Dinosaurs from the Cedar Mountain Formation
Genus	Species	Member	What was found	Notes	Images
Cedrorestes	Cedrorestes crichtoni	Upper Yellow Cat Member			Eolambia Hippodraco Iguanocolossus Tenontosaurus Zephyrosaurus being attacked by a Deinonychus
Eolambia	Eolambia caroljonesa	Mussentuchit Member
Hippodraco	Hippodraco scutodens	Upper Yellow Cat Member
Iguanacolossus	Iguanacolossus fortis	Lower Yellow Cat Member
Iguanodon	Iguanodon ottingeri		Teeth.	Doubtful.
Planicoxa	Planicoxa venenica	Poison Strip Member	Connected body bones.
Tenontosaurus	Tenontosaurus tiletti	Mussentuchit Member		Most common beaked dinosaur in the area.
	Indeterminate	Ruby Ranch Member		Most common beaked dinosaur in the area.
Zephyrosaurus	Zephyrosaurus schaffi	Mussentuchit Member

Long-necked Dinosaurs (Sauropods)

Long-necked Dinosaurs from the Cedar Mountain Formation
Genus	Species	Member	What was found	Notes	Images
Abydosaurus	Abydosaurus mcintoshi	Mussentuchit Member			Abydosaurus Astrodon Brontomerus Cedarosaurus Moabosaurus
cf. Astrodon	Indeterminate	Ruby Ranch Member.
Brontomerus	Brontomerus mcintoshi	Ruby Ranch Member
Cedarosaurus	Cedarosaurus weiskopfae	Upper Yellow Cat Member	Body skeleton.
Mierasaurus	Mierasaurus bobyoungi	Lower Yellow Cat Member
Moabosaurus	Moabosaurus utahensis	Poison Strip Member	Remains of at least 18 partial individuals.
Venenosaurus	Venenosaurus dicrocei	Poison Strip Member	Partial body skeleton.

Meat-eating Dinosaurs (Theropods)

Meat-eating Dinosaurs from the Cedar Mountain Formation
Genus	Species	Member	What was found	Notes	Images
cf. Acrocanthosaurus	Indeterminate	Ruby Ranch Member.			Acrocanthosaurus Deinonychus Falcarius Geminiraptor Moros Nedcolbertia Siats Utahraptor Yurgovuchia
Deinonychus	Indeterminate	Mussentuchit Member.
Falcarius	Falcarius utahensis	Lower Yellow Cat Member.
Geminiraptor	Geminiraptor suarezarum	Lower Yellow Cat Member.
Martharaptor	Martharaptor greenriverensis	Upper Yellow Cat Member.
Moros	Moros intrepidus	Mussentuchit Member.
Nedcolbertia	Nedcolbertia justinhofmanni	Upper Yellow Cat Member.	Partial skeletons of three individuals.
cf. Richardoestesia	Indeterminate	Mussentuchit Member.
Siats	Siats meekerorum	Mussentuchit Member.	Partial body skeleton of a young individual.
Utahraptor	Utahraptor ostrommaysi	Upper Yellow Cat Member.	Skull and body fragments.
	Indeterminate	Poison Strip Member.
Yurgovuchia	Yurgovuchia doellingi	Lower Yellow Cat Member.

Other Fossils

Map of Utah showing the location of the Cedar Mountain Formation (red).

Besides dinosaurs, the Cedar Mountain Formation has many tiny fossils, mostly teeth from different animals. These "microfossils" are found by washing rock through screens.

• Fish: Scientists have found teeth from ancient freshwater sharks (like Hybodus), rays, lungfish (Ceratodus), and other bony fish. Lungfish are cool because they can breathe air when water has low oxygen!
• Amphibians: Some salamanders and frogs have been found, but they are rare.
• Reptiles: Many reptile fossils are present, including aquatic turtles (Glyptops, Naomichelys), at least one type of snake (Coniophis), and several different lizards. Crocodiles are also found, but only in pieces. There's even a fragment of a large flying reptile called a pterosaur.
• Birds: Bird fossils are very rare because their bones are delicate. At least one ancient aquatic bird has been found.
• Mammals: Many small mammal fossils have been discovered, including early types of mammals like triconodonts, symmetrodonts, multituberculates, and even one of the earliest marsupials (Kokopellia).

Other types of fossils include:

• Charophytes: These are distinctive structures from freshwater algae. They are so unique that they help scientists match rock layers of similar ages.
• Ostracods: These are tiny crustaceans with shells that look like clams.
• Pollen: Found in the Mussentuchit Member, pollen helps scientists figure out what the environment was like long ago.
• Petrified Wood: In some places, large petrified (fossilized) logs are found, especially in the Poison Strip. These logs are from ancient conifer trees that were over 30 meters (100 feet) tall! The unique wood of the tree fern Tempskya is also sometimes found.

Other Reptiles

Fragments of pterosaurs (flying reptiles) have been found in the Mussentuchit Member.

Crocodilians

Crocodilians of the Cedar Mountain Formation
Genus	Species	Member	What was found	Notes	Images
cf. Bernissartia	cf. Bernissartia sp.	Mussentuchit Member			Bernissartia
Dakotasuchus	Dakotasuchus kingi	Mussentuchit Member.

Lizards and Snakes

Turtles

Turtles of the Cedar Mountain Formation
Genus	Species	Member	What was found	Notes	Images
Glyptops	Glyptops sp.	Yellow Cat Member, Mussentuchit Member			Peripherals
Naomichelys	Naomichelys sp.	Mussentuchit Member.
gen. nov.	sp. nov.	Yellow Cat Member

Amphibians

Amphibians of the Cedar Mountain Formation
Genus	Species	Member	What was found	Notes	Images
Albanerpeton	Albanerpeton cf. A. nexuosus	Mussentuchit Member			Albanerpeton

Fish

Bony Fish

Bony Fish of the Cedar Mountain Formation
Genus	Species	Member	What was found	Notes	Images
Semionotus?	Semionotus? sp.	Yellow Cat Member			Semionotus Ceratodus
Ceratodus	C. kempae	Yellow Cat Member
	C. kirklandi	Yellow Cat Member
	C. molossus	Mussentuchit Member

Cartilaginous Fish

Cartilaginous Fish of the Cedar Mountain Formation
Genus	Species	Member	What was found	Notes	Images
Hybodus	Hybodus sp.	Ruby Ranch Member, Mussentuchit Member			Hybodus
Polyacrodus	Polyacrodus parvidens	Mussentuchit Member
Lissodus	Lissodus sp.	Mussentuchit Member
Ischyrhiza	Ischyrhiza sp.	Mussentuchit Member
Pseudohypolophus	Pseudohypolophus sp.	Mussentuchit Member
cf. Baibisha	New species	Mussentuchit Member
Cretorectolobus	Indeterminate	Mussentuchit Member

Mammals

Images for kids

• 

  Gastonia

• 

  Cedarpelta

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  Animantarx

• 

  Peloroplites

• 

  Cedrorestes

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  Eolambia

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  Hippodraco

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  Tenontosaurus

• 

  Brontomerus

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  Cedarosaurus

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  Mierasaurus

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  Falcarius

• 

  Geminiraptor

• 

  Martharaptor

• 

  Moros

• 

  Utahraptor

See also

In Spanish: Formación Cedar Mountain para niños