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Coelophysis in the Upper Triassic Chinle Group

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Hidden : 06/14/2018
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Geocache Description:

Welcome to the Ghost Ranch! If you've just pulled up to the parking coordinates, you are at the Ghost Ranch visitor center. Please make sure to sign in at the visitor center and let them know your destination. There is a $5.00 conservation fee payable at the Welcome Center that allows guest access to hiking trails, labyrinth, Museums, bathroom facilities and campus grounds. You can also get information about the hike here. For this earthcache, you will be hiking a portion of the Kitchen Mesa trail. The posted coordinates will take to you a location to learn more about the Chinle Formation and Coelophysis Quarry. Expect about 1.5 mile round trip hike with only a small amount of elevation gain. Be sure to bring water and sun protection, especially in the hot seasons. Dogs are allowed as long as they are kept on a leash and under your control. The Ghost Ranch staff want to remind all visitors to stay on marked paths and not to take anything (rocks, fossils, flowers) from the property.

How to hunt dinosaur fossils: Know your rock formations!

If you are going to look for dinosaur fossils, particularly if you are targeting species from a certain time period, one of the best ways to go about it is to understand the age of the different rock formations of the landscapes you are in. If you can identify rock formations from a time period matching that of the dinosaurs you are wanting to find, you will have a basis for where to start your search. And by "rock formations" I don't just mean how the rocks around you look. I mean rock formation in the stratigraphic sense of the word. Stratigraphy is a branch of geology that studies the layers of rock and there are all sorts of field specific nomenclature they use but what is useful for this Earthcache is the term formation. A formation, in the stratigraphic sense, is a description of some rock's visible physical characteristics. If a bunch or rock you see in a cliff all looks the same, it is part of the same formation. In many places, only one formation is visible, and the usefulness of this term may not be readily apparent. but in places like the grand canyon, or even right here at Ghost Ranch, multiple rock formations are readily discernible.


Rock formations of Kitchen mesa, easily visible from GZ of this Earthcache.

Over time geologists and stratigraphers have studied different rock formations and mapped out where they occur. The USGS has all sorts of cool maps that you can browse and explore. But it isn't just about mapping, these scientists have also dated the formations using a variety of methods and from this knowledge you can tell a lot about how an area formed. Here at the Ghost Ranch there are three main rock formations that are visible. The Chinle Formation, Entrada Sandtone, and the Todilto Formation.

The oldest exposed rock formation at the Ranch is from the Upper Triassic Chinle group, which can be traced back to the Chama Basin. It can be determined to be the oldest by very simply logic, it is the bottom layer. The younger formations were deposited afterwards and are therefore on top of it. The rocks of the Chinle Formation are brick red to grayish green in color consist of sediments deposited by rivers around 205 to 228 million years ago. When these sediments were being deposited, the tectonic plates under the Ghost Ranch area were situated at about 10 degrees north of the equator so it was a more tropical and warmer place. The reddish brown mudstone that you see at the bottom of kitchen mesa is part of the Upper Triassic Chinle group of the Chinle formation. This is the same group that is also found at Petrified Forest National Park in Arizona, another place where many cool fossils have been found. There are other, older, groups that are part of the Chinle Formation, some in the Ghost Ranch borders, but this Earthcache does not lead you to those.

If you are going to be looking for dinosaur fossils from the late Triassic, the Upper Chinle group is a good place to start your search. Not only is the time that the rock was being formed match up to when dinosaurs were present, but the location of this area was in a climate that would have had abundant life. The type of sedimentary rock here, mudstone and siltstone, is created from sediment being deposited by river flows and as these can sometimes occur very quickly during floods, it creates the conditions necessary for animal remains to become rapidly buried and then preserved. All these factors make areas like this one great for fossil hunting.

Coelophysis Quarry

In 1947, members of the American Museum of Natural History, were visiting this area while on their way to Triassic era formations in Arizona, when they stumbled across a remarkable site in the Chinle Formation of the ghost Ranch. They were expecting to find bone fragments and maybe a partial skeleton. However, after a few days of careful exploration they uncovered hundreds of preserved skeletons in a dense bonebed. Many of these would later be identified as Coelophysis bauri. Because of the way the skeletons overlapped and were tightly packed together in the red silt-stone, large blocks were quarried out of the bedrock and shipped to various institutions through out the US including the American Museum of Natural History, the Carnegie Museum and the Smithsonian. Once there, careful teams of paleontologists could extract full skeletons of the little dinosaur and the numerous specimens allowed for rich research into the paleobiology of the Coelophysis.


Left: Coelophysis bauri skull. Right: Artist rendition of Coelophysis

Coelophysis is a small dinosaur in the Theropoda group, the same group that contains such giant meat eating dinosaurs such as T. rex, but also contains modern birds. Coelophysis had a long slender body that stood upright on two legs, a long neck and tail and a relatively small head. Evidence suggests that Coelophysis was a swift predator that fed on smaller animals.


Time calibrated dinosaur family tree

There is a ton of great information about Coelophysis on the web. Even better, the Paleontology Museum at the Ghost Ranch has an incredible exhibit on this dinosaur and others found here. There is a reference waypoint (N 36° 19.823 W 106° 28.471) included for the location of the museum and it is well worth a visit. This little dinosaur is also special point of pride for New Mexicans as it is the Official State Fossil. But this is a geology lesson, not paleontology so I'll leave it at that.

Earthcache Tasks

In order to log this earthcache as found go to the posted coordinates to learn more about the Coelophysis Quarry and to see the Chinle Formation up close and personal. Then send me your answers to the following questions. .
1.  How much farther southeast was this site located 205 million years ago, when the red mudstone and siltstone was deposited. Why is this important to know if you are hunting for fossils?
2. About 230 million years ago, hundreds of Coelophysis died at this spot. How were they probably buried and about how long did it take for the Chinle formation to bury them.
3. Closely examine the mudstone rock in this area. Describe the composition and grain size of the rock. What clues might this tell you about how this layer was deposited?
4. Why, in your own words, is the Upper Triassic Chinle formation a good place to look for dinosaur fossils?



Coelophysis, the New Mexico State Fossil, New Mexico Earth Matters newsletter Summer 2017.
website link:

Schwartz, Hilde L., and David D. Gillette. “Geology and Taphonomy of the Coelophysis Quarry, Upper Triassic Chinle Formation, Ghost Ranch, New Mexico.” Journal of Paleontology, vol. 68, no. 5, 1994, pp. 1118–1130. JSTOR, JSTOR,


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