Snapshot in Stone


National Park Service

The Glen Canyon Project involves systematically and painstakingly searching every exposure of the Glen Canyon Sandstone, both near roads and far into the backcountry. In one remote canyon, paleontologists came across a steep rock surface covered with small tracks. When the area was a sand dune, the tracks were made low on the steep side. The preservation is remarkable, probably because there was enough dew on the slope to hold the prints in place long enough to be buried. On one hand, it's an amazing coincidence—no other surfaces like this have been found. But on the other hand, think about how many other nights this dune must have been covered with tracks. Over a long enough time period (say, 20 million years), amazing coincidences become a near certainty.


National Park Service

The most abundant track on this surface is Brasilichnium, made by a small mammal-like reptile. Each footprint is about the size of a dime, and there are hundreds of them. The largest group of Brasilichnium in the Glen Canyon prior to this find was seven individuals. This newly discovered site contains several hundred. Each of the little printsis accompanied by a crescent of pushed-up sand on the downslope side; exactly what happens when you climb a sand dune. Some of them are just divots, but some of them have well-preserved toe impressions, as you can see in the photo to the right


National Park Service

Nearby there is a trail made by what must have been quite a large scorpion. When scorpions walk, all four legs on one side hit the ground at about the same place, making their tracks look like they were made by something with toes. The leg spread on this trackway is about four inches (10 cm). The paleontologists thought they might be able to figure out how big the scorpion was from the leg spread, but the little data that there is doesn't show a correlation between leg spread and body size.

Dinosaur National Monument was created to protect resources just such as this trackway site. As you can see from the top photo above, these tracks are located on a very steep slope. It is difficult to move around on and difficult to take pictures. It presents special challenges to paleontologists: the slab is too big and too fragile to be collected. It has already been damaged by erosion. The usual procedure is to make a mold of the surface with putty or liquid latex, but this surface is too big and steep for that to be feasible. Other methods, such as laser imaging, are being explored, but for now, it's a good thing Dinosaur National Monument is here to protect it.


Last updated: February 24, 2015

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