Ancient Mammal Footprints Excite Paleontologists at Dinosaur National Monument

Top: Paleontologists Dan Chure and George Engelmann examine the trackway they recently found at a remote site in Dinosaur National Monument. Bottom: Some of the fossil foot impressions are amazingly detailed. NPS photos.

Earlier this month, eagle-eyed paleontologists doing field work at Dinosaur National Monument spotted something that gave them an adrenaline rush. On a canyon wall they noticed numerous tiny fossilized footprints left by mammals and other animals that lived about 190 million years ago during the Early Jurassic. At that time a vast area consisting of Utah and Wyoming and parts of Colorado, Arizona, and New Mexico had a severe desert climate and a landscape featuring huge sand dunes and a prevailing scarcity of water, vegetation, and animal life.

This was an exceptional find. Mammal tracks were not commonly fossilized in ancient sandy terrain, and to discover such a huge collection of tiny tracks -- most dime-sized, some smaller -- left by the primitive mammals of that long-ago era is electrifying. Monument paleontologist Dr. Dan Chure and University of Nebraska-Omaha paleontologist Dr. George Engelmann, now in their fourth year of studying the Glen Canyon Group in the monument, will relish the discovery for the rest of their lives.

The steeply slanting canyon wall where the tracks were found (see photo) was once the face of a towering sand dune. Tiny nocturnal animals skittering across a thin crust of dew-moistened sand left tracks on the dune that were quickly covered and eventually fossilized. The scientists who discovered the footprints – hundreds and hundreds of them -- nearly a fifth of a billion years later were simply amazed at what they saw. Many footprints left by the little rat-sized mammals are so detailed that you can make out individual toe impressions.

Some of the fossil footprints at the track site (trackway) are interesting because they provide valuable information about the creatures that were able to make a living in the incredibly harsh desert environment that prevailed here during the Early Jurassic. This was a time when tiny primitive mammals eked out a precarious living in a dinosaur-dominated world. Indeed, some tracks mixed in with the mammal tracks appear to have been left by small dinosaurs. An underlying (earlier-laid) rock layer contains fossil foot impressions left by a scorpion that had a four-inch leg span.

Preserving the trackway is a high-priority task. It’s clear that some of the surface, which probably contained thousands of tiny footprints, has already eroded away.

Scientific study of the site is scarcely underway. It will take years to properly document and study this treasure trove. Since the trackway is in a remote location, and also reposes at a steep angle, it will be very challenging work to map the trackway horizon, count the tracks, determine which creatures made which tracks, etc. One intriguing question is why there are so many tracks at this particular location.

The track site is not open to the public, but there are plans to replicate a representative sample of the footprint-bearing rock layer for exhibit at the Monument. Meanwhile, visitors who want to see fossils are invited to hike the monument’s Fossil Discovery Trail and enjoy the dinosaur fossils that can be seen in the rocks along the trail.

Comments

Thanks Bob for all the interesting things you guys put out for us to see. what a find! looks liked a little 4 fingered hand print. i was wondering if there might have been claw marks that wore away. so many amazing things in this world of ours , that have never been seen. keep up the good work. i enjoy this site a ton.

Thanks for writing, azborn2001. It's always nice to get positive feedback and interesting comments/questions. I don't know about any claw marks that might be visible in the footprint impressions at this particular trackway. Maybe somebody in the know will chime in on this one. While I have your attention, let me point out something that you may not have noticed in the footprint photo accompanying this article. The ridge of sand at the base of the paw print shows that the animal that left this print was headed up the dune, not down it.

Good question about the claw marks. The mammal tracks we found were made in dune sand which does not often preserve such fine features as toes, much less claw marks. While claws were undoubtedly present in the trackmaker the dry sand of the dune would have collapsed and filled them in. Other kinds of sediments, such as wet mud along a lake, pond, or stream margin would be a much better medium for preserving claw marks.

If you hike in the morning in an area where there are sand dunes or flats, look at the sand and you will see the tracks of rodents about the same size as the ones we found in Dinosaur. The fine details are usually vague or missing. Compare that to tracks along a river shoreline and notice the difference.

Thank you very kindly, Dr. Chure. (Man, when you invite somebody "in the know" to chime in, you never know what you're going to get!) Since you are one of the scientists who found this amazing site, is there any other personal observation that you'd like to make? And BTW, which one of the guys in the top photo is you?

The Glen Canyon Group, also known as the Navajo Sandstone or Nugget Sandstone, has traditionally been considered a poor place to look for fossils. Well it is, but just not as poor as some have thought. Over the last 5 years Spencer Lucas and George Ogier have documented in the Moab area extensive horizons with vertebrate and invertebrate burrows that extend for kilometers. Judy Parrish and her students have published on tree trunks up to 2 feet in diameter preserved upright in the Navajo, indicating that permanent bodies of water must have been present at least locally for long periods of time. In our work in Dinosaur and its environs we have found colonial insect nests and vertebrate burrows, abundant dinosaur footprints, and spring mounds where carbonate rich waters came out of the ground. At the mounds we have several different kinds of freshwater snails, the first reported from these desert deposits. What their biology was remains to be figured out. We even have some very interesting dinosaur skeletal remains. Still, doing paleontological work in the Glen Canyon requires a dedication to walk out all the outcrop and check every nook and cranny, because some of these sites are fairly small and can easily be overlooked. The Glen Canyon was a nasty place to live in overall, but oasis-like deposits were more common than previously thought. One just has to find them. Now that we know that primitive mammals were at least locally common in our study area, we only have to find the horizon where all those little furballs are fossilized inside their burrows.

And I am the one on the right in the NPS green and gray.

Thanks, Dan. This is fascinating stuff. Sounds like you'll need several lifetimes to get the Glen Canyon Group facts sorted out. Will you at some point be seeking volunteer workers for this project?

Thanks Dan for all the info,very interesting to me. please keep us posted about your work. thanks,max

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