Red Gulch Dinosaur Tracksite:
A BLM Educational Adventure
A chance stop on a rippled bedrock surface by geologists Erik Kvale (Indiana University) and Allen Archer (Kansas State University) and local naturalists Row Manuel, Cliff Manuel, and Fran Paton in May of 1997 led to the discovery of one of the most extensive dinosaur megatracksites in North America. The dinosaur tracks were made by small- to medium-sized two-legged (bipedal) dinosaurs that walked along an ancient white sand beach 167 million years ago during the middle part of the Jurassic Period. At that time a vast inland sea extended from Alaska right through eastern Idaho, Montana and into Wyoming with the deepest part of the seaway along the western margin of Wyoming. The nearby town of Shell would have been a beach resort town if it had existed then and would have had a climate much like the Bahamas do today. They were the first middle Jurassic dinosaur tracks discovered in the Wyoming and Montana region.
​
Until the late 20th century, dinosaur track-bearing horizons were largely unknown in Wyoming, but since the 1990s they have been found in every Jurassic-age formation in the Greybull/Shell area. Some of these horizons extend to the Montana-Wyoming border and as far south as Tensleep. The most exceptional of these are now part of a 40 acre BLM dedicated educational site which preserves thousands of dinosaur tracks and constitute the most concentrated accumulation of publicly accessible dinosaur tracks in Wyoming.
This image represents what a view looking west from Shell, Wyoming 167 million years ago would have looked like. Just imagine some two-legged dinosaur walking past you.
If you scoop up some sand from beaches in the Bahamas or Florida Keys and look carefully, you will notice that, in many cases, the sand is composed of tiny spherical grains of carbonate and a few broken shell fragments. The tiny sand-sized spheres are called “oolites”. This is exactly what the RGDT beaches are composed of except have now been turned to rock.
Reconstruction of the Sundance seaway (Kvale et al., 2001, PALAIOS, v. 16, p. 233–254). Note that the seaway is much wider across Wyoming and Montana than further south or north.
Directions To The Tracksite
Where Are You Stratigraphically?
What Can You See?
Track Maps
Directions To The Red Gulch Dinosaur Tracksite
Where are you stratigraphically?
While the chart on the left may look a bit intimidating to a non-geologist, it is a geologist’s attempt to simplify what they see in the outcrops around them. The different patterns reflects the rock types that lie immediately below the tracksite and the rocks that occur above the horizon. The symbology indicates all of the geological formations that contain dinosaur or reptilian tracks in the Greybull-Shell area.
​
The chart on the right is a simplified summary of the geological formations that exist in the Big Horn Basin. The stratigraphic position of RGDT is indicated in yellow. The numbers to the left are the ages of the rocks in millions of years. The Sundance Formation Red Gulch Dinosaur Tracks are approximately 167 million years old.
What can you see?
The Red Gulch Dinosaur Tracksite (RGDT) is a 40-acre Bureau of Land Management (BLM) educational site. Within this area are literally thousands of dinosaur footprints made by small- to medium-sized bipedal (walked on two legs) dinosaur that walked with three toes on the ground. It is best to view these tracks in early morning or later in the afternoon when the sun casts a low-angle light on them. Besides the tracks, there are other features that give geologists an indication of what type of dinosaurs these animals were, what the area looked like 167 million years ago, and what sort of climate these dinosaurs experienced.
The Red Gulch Dinosaur tracks were made by walking two-legged (bipedal) dinosaurs. The prints preserve three toes (tridactyl). Many of the tracks resemble those made by theropod (meat-eating) dinosaurs although some clearly look more like small plant-eating ornithopods. Figure is from Lockley and Hunt, 1995, Dinosaur Tracks, Columbia University Press.
The identification of the trackmaker as either theropod or ornithopod is based largely on the shape of the middle toe. Theropod dinosaurs tend to have had long middle toes that were slightly sinuous and tapered indicating claws. Few of the tracks show any sign of a heel indicating that these dinosaurs were “toe-walkers."
If you look carefully, you can still see the remnants of the ripples in the bedrock (“wrinkles” running left to right) that first attracted the attention of the discovers of RGDT. However, other features are also obvious including the irregular depressions, labeled “AB’s, that disrupt the rippled surface.
Many example of small irregular depressions can be seen on the RGDT surface. Initially researchers didn’t know what to make of them. However a trip to Florida by the researchers Erik Kvale and Gary Johnson (Dartmouth College) solved that mystery. Modern tidal flats often show similar features. They can be seen here on Pine Island (Cape Coral), Florida. As the tide withdraws (ebbs), the sandy surface takes on a greenish hue. This indicates the presence of algae growing in the sediments. When the algae gets thick enough it can actually form a mat that can stabilize the sediments preventing or slowing its erosion.
​
If the mat surface was penetrated by walking animals, clams, worms or shrimp burrowing into the sediments, the next tide or storm can erode the mat at those points of disruption resulting in the erosional depressions. (labeled “AB”).
​
This figure shows an erosional depression in the RGDT surface with a dinosaur track superimposed on it indicating that the dinosaur stepped on the mat surface after the AB formed.
Body fossils of clams, worms, or shrimp that might have once lived in the sediments that now make up the surface populated by dinosaur tracks are sparce or absent. However the remains of their life activities (called “trace fossil”) like the burrows they lived or fed in cover the surface. Several of these are shown here. Skolithos is a vertical burrow once inhabited by a worm-like organism. Rhizocorallium (U-shape, inclined) and Diplocraterion (U-shaped, vertical) are scientific names for burrows that may have been generated by shrimp or clams. These types of trace fossils are common on modern tidal flats. The Skolithos traces are coeval (formed at the same time) with the dinosaur tracks but the Rhizocorallium and Diplocraterion traces occurred sometime after the dinosaurs walked on the surface.
If you look carefully when the sunlight is striking the RGDT surface at a low angle (winter is a great time to view the track surface), you might see cube-shaped features that look like a small blocks of wood on edge. These are the remains of ancient salt (halite) crystals that grew in the RGDT beach sands when the sands were still soft and uncemented. Salt crystals only grow in dry climates when evaporation is high. Thus, these features indicate that the climate these dinosaurs lived in was, at least seasonally, arid. Dinosaurs didn’t always live in jungles and this is proof of that.
As you walk around the RGDT area, you might notice large fragments of these two fossils. They are two of the most ubiquitous marine fossils in the Sundance Formation. The toenail-shaped fossil is the oyster Gryphea nebrascensis (aka “dinosaur” or “devil’s toenail”). It is a common fossil in the rocks that immediately overlie the RGDT surface. The other fossil is of a squid-like organism called a “belemnite” (Pachyteuthis densus). If you find it on the tracksite surface it is because it has washed down from sediment above the layers that contain the Gryphea. The artwork is by Russell Hawley (Tate Museum).
Ants are wonderful collectors for geologists and paleontologists. The anthills in the RGDT area are full of small fossils such as these, below. These include snails (gastropods), sponges, crinoids (aka “sea lilies” – flower-shaped animals that are related to starfish), and bivalves like clams (pelecypods). The ants are helping us understand the abundance and diversity of organisms that once lived in the Sundance Sea.
Track Maps
The map on the left shows was created by Dartmouth College students of a 540 square foot portion of the RGDT surface. The map shows the orientation of the dinosaur tracks, invertebrate burrows, and irregular erosional depressions known as “ABs”. The map on the right showing only dinosaur tracks. Notice the preferred southwest orientation of most of the trackways. These tracks and trackways are only a small percent of the tracks that exist in the RGDT area. There is one trackway made by a larger three-toed dinosaur that moved to the northwest. Why might he have been moving in that direction? No one knows, so your guess is as good as any other.
This map shows dinosaur trackways in an area removed from the main BLM site. Note the predominance of tracks heading towards the southwest