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.