April 30, 2016

By Martin Lockley

For more than a century, the Western Slope of the Rocky Mountains where the mountains descend across the Colorado-Utah border onto the Colorado Plateau has proved a bountiful source of dinosaur fossils. In 1900, the giant Late Jurassic sauropod, Brachiosaurus, was first found in the now world-famous Morrison Formation near Fruita, Colo. Bones in the dinosaur graveyard we now know as Dinosaur National Monument near Vernal, Utah, were discovered starting in 1908 with a Diplodocus femur, followed in 1909 by a nearly complete Apatosaurus and many more dinosaur bones over the ensuing years. These finds — along with multiple others closer to Denver in the late 19th century — set off a fossil-hunting bonanza across the West.

President Woodrow Wilson designated the area east of Vernal as Dinosaur National Monument in October 1915. Studies and excavations continued at the site, and in 1938, President Franklin D. Roosevelt expanded the monument’s borders by 81,000 hectares, extending its reach into Colorado. In the 1960s, Price, Utah, got into the dinosaur game when the town bought a replica of an Allosaurus — another Morrison Formation dinosaur — as a tourist attraction, helping found what is now the Prehistoric Museum. These sites — Fruita, initially a “Dinamation” site but as of 2000, the site of Dinosaur Journey, a branch of the Museums of Western Colorado, and Vernal, considered the gateway to Dinosaur National Monument — marked the eastern and northern corners of what became known as the “Dinosaur Triangle.” The museum in Price defined the western corner.

Then, in 1997 and 1998, respectively, the Colorado and Utah state legislatures independently designated a new “Dinosaur Diamond” scenic byway: an 824-kilometer-long roughly diamond-shaped dinosaur-sightseeing route that included Moab as its southern point. Moab had, by this time, become a bustling tourist destination mainly due to its proximity to Arches and Canyonlands national parks. Conceptually, the Dinosaur Diamond also included other neighboring communities like Blanding, Utah — about 120 kilometers south of Moab — which created its own Dinosaur Museum in 1995 . So, by 1998, with Blanding included as the southern corner, the Dinosaur Diamond had regionally important dinosaur museums at all four corners. In 2015, Moab got its own dinosaur museum called Moab Giants, which was built to celebrate the large number of dinosaur tracks — and the animals that made them — found in the region.

Should you find yourself in this neck of the woods, head to Dinosaur National Monument, Dinosaur Journey, or Prehistoric Museum for immersion in the Late Jurassic world of Stegosaurus, giant sauropods and more, or make tracks to Moab Giants and Blanding’s Dinosaur Museum for stories, exhibits and experiences focused on tracks, trackmakers and the trackers — the paleontologists who specialize in tracks. The museums of the Dinosaur Diamond showcase the diversity of ancient habitats that reflect the varied geological landscapes of the area, and which continue to be illuminated in more detail with further scientific study and with each new find.

One of the best aspects of these museums is how they constantly adapt to new discoveries. Over the last century or more, paleontologists have gone from believing that dinosaur tracks were rare and of little scientific significance to recognizing that they are far more abundant than bones and are actually of fundamental importance in demonstrating behavior and providing census data on dinosaur communities. It’s all thanks to continuing excavations and discoveries.

Starting in the Late Triassic and Early Jurassic Near Moab

In the Dinosaur Diamond region, some of the most important and most recent trackway finds have been around Moab and have been dated to between 210 million and 160 million years ago, spanning from the Late Triassic to the Early and Middle Jurassic. During the Late Triassic, the area was covered with lush subtropical habitats, giant horsetails, fish- and amphibian-filled lakes, and turkey- sized carnivorous dinosaurs like Coelophysis, the New Mexico state fossil. This animal and its anatomically similar relatives left an abundance of small, birdlike three-toed tracks first reported in New England in the mid-1800s and called Grallator. The earliest Grallator tracks were all small. Thus track specialists recognized a zone of strata, found over much of the world, packed with small footprints from the dawn of the age of dinosaurs.

We can follow the evolution of such early theropod dinosaurs through various family tree branches into the Jurassic formations represented in the Moab area. Here, larger theropod relatives left tracks, up to 45 centimeters long, such as Eubrontes, literally meaning “true thunder” but loosely translated as “earth shaker.” The trackmakers that left Eubrontes tracks were abundant at this time due to an evolutionary radiation of theropods, meaning there are many well-preserved examples to be found. Another interesting track, named Otozoum, meaning “giant animal,” also found first in New England in the mid-1800s, was unknown elsewhere until examples were found in Moab in 1990. It represents a prosauropod, an ancestral relative of giant sauropods like Apatosaurus and Brachiosaurus, which themselves did not debut until the Late Jurassic.

Transitioning from the Late Triassic to the Early Jurassic, the rock record indicates that the region was covered in huge, Sahara-like deserts with endless tracts of scorching, barren sands. The famous Navajo Sandstone, seen at the entrance to Arches and along the Colorado River south of Moab, is the classic example of fossilized dunes. Thus, it was a surprise to learn in the 1970s that, in many areas, tracks of desert dwellers were quite abundant at hundreds of sites around Moab and all across southern Utah. Previously, paleontologists thought desert environments would have been too harsh to sustain trackmaking animals. It appears that while theropods and prosauropods roamed the intermittently dry water courses in interdune and small oasis areas where one might expect to find tracks, tracks of small rodent- and cat-sized protomammals (or synapsids), named Brasilichnium, are common on the downwind, or lee, side of the ancient dunes. Their tracks also almost always point uphill, heading nose into the wind. No one really knows why this is.

The Early Jurassic theropod and prosauropod tracks Grallator, Eubrontes and Otozoum, together with a small ornithischian track known as Anomoepus, are typical of what has been called the first global track zone, or “biochron,” showing very similar track assemblages in the eastern U.S., Europe, Asia and Africa. However, it is only in the western U.S. that Early Jurassic protomammal tracks are common. This is because it is only in this region that these animals’ preferred sandy desert habitats prevailed at this time.

Tracks Through the Middle and Late Jurassic

Desert habitats again prevailed during the Middle Jurassic when the Entrada Sandstone was deposited. The Entrada remains today as the main arch-forming rock formation in Arches National Park. Protomammals evidently disappeared throughout much of the world by this time, but we still find the small, three-toed tracks of crow-sized theropods.

This widespread track layer has also popularly been referred to as the “Dinosaur Freeway.” The explanation of why there are so many tracks here is as much geological as biological; it has to do with rising sea level across a wide coastal plain. Counterintuitively, rising sea level does not wash away tracks. Instead, the sea acts as a dam allowing river and other shoreline sediment to accumulate along the coast creating coastal plain deposits — a process known as aggradation. As the sea transgressed farther over formerly dry land, dinosaurs tramped up and down the shifting coastlines, leaving behind millions of footprints. During this period, we also see evidence in preserved tracks for an influx of pterosaurs, which fed in the shallow waters and left their footprints on the ripple-marked shoreline sands.

In the Late Jurassic, the marine incursion began to regress, and the Western Slope of the Rockies became less arid. During this time, the Morrison Formation — comprising sandstones interbedded with soft mudstones — was deposited in a region extending from New Mexico to the Canadian border. The paleoenvironment was a broad mosaic of rivers, lakes, ponds and floodplain soils that offered suitable habitats for a diverse flora and fauna, including some of the world’s most famous dinosaurs like Allosaurus, Apatosaurus, Diplodocus, Brachiosaurus and the Colorado state fossil Stegosaurus.

To this list of iconic creatures, all found abundantly in the Dinosaur Diamond area, we can add many other denizens of Morrison time, including the crocodilian Fruitachampsa and the digging mammal Fruitafossor, both named for Fruita, where they were found. Another famous denizen, especially in the Moab area, is the sauropod Dystropheus, first identified by John Macomb’s 1859 expedition, which slogged from Santa Fe across rugged terrain to the confluence of the Green and Colorado rivers. This was 18 years before the discovery of dinosaur bones at Morrison, Colo., in 1877, often reported as the seminal discovery that opened the west to paleontological exploration and the infamous “Bone Wars” between paleontologists Othniel Marsh and Edward Cope.

Late Jurassic-aged Morrison paleoenvironments were not just dinosaur habitats, they were also home to a diverse fauna of small mammals and a flora often described as a fern- and cycad-dominated savanna. Unlike the theropod-dominated assemblages from the older Entrada Sandstone, the collection of tracks in the Morrison Formation make ecological sense. They include those of large and small theropods, sauropods and a few ornithischian dinosaurs, crocodiles and turtles, thus generally reflecting the presumed composition of the fauna, based on excavated bones.

Traipsing into the Cretaceous

As we step into the Cretaceous, we find ourselves in the 120-million- to 110-million-year-old Cedar Mountain Formation, which has proved highly productive for dinosaur remains in the Moab area. We also find tracks that match the skeletal record quite well. Theropod footprints include the first two-toed dromaeosaur tracks found in North America, quite possibly belonging to Utahraptor, now an iconic Dinosaur Diamond discovery, for its large size. Sauropod and Iguanodon-like tracks also match the skeletal record, but a dense assemblage of shorebird-like tracks is significant, because, as yet, the deposit has yielded no bird bones.

In Colorado alone, trackers have recorded more than 100 significant sites bearing tracks of birds, theropods, ornithopods, ankylosaurs, crocodilians, pterosaurs, turtles and even horseshoe crabs. Not a single sauropod track has been found, however. We don’t know exactly why, but sauropods disappeared from North America for about 30 million years, reappearing about 70 million years ago. This gap in the record is called the “sauropod hiatus.”

The track-rich beds of the Dakota Sandstone represent a huge dinosaur freeway — far larger than the Middle Jurassic example in southern Utah — extending from Kansas, Oklahoma and northeastern New Mexico across Colorado and into Utah. All tracks were not registered simultaneously across this vast area. Rather, as sea level rose and the shoreline advanced westward across the region, coastal plain deposits developed kilometer by kilometer. First thought to cover only eastern Colorado, scientists now realize that this is the mother of all dinosaur freeways.

New evidence gives us tantalizing clues about how fast the coastline shifted as seas advanced westward across what is now the Dinosaur Diamond, as well as how many generations of dinosaurs wandered along this shifting shoreline. The latest big track discovery in the Dakota Sandstone comes from near Delta, Colo. It consists of dozens of large bowl-shaped excavations, up to 2 meters across, showing clear scrape marks made by the claws of both the left and right feet of large theropods. Clearly, these scrapes indicate a lot of energetic digging, but why? The only explanation that fits the evidence is that these features represent “nest scrape displays,” which are quite common today among various ground-nesting bird species. There don’t appear to have been actual nests at this site; the distinct claw scrapes were not smudged out by animals sitting in them for long periods during incubation, and there are no eggs, eggshells or remains of baby hatchlings.

The final chapter in the Western Slope dinosaur odyssey was written, appropriately, in the “Book Cliffs” mountain range that extends east-west across the Dinosaur Diamond from near Fruita to Price. Massive sandstones that make up the Late Cretaceous Mesa Verde Group represent extensive coastal plain deposits laid down as the Western Interior Seaway regressed back eastward across the area. Again, the region was well-vegetated and conducive to accumulation of peat and tracks. The peat was destined to become coal and drive the local mining industry, especially around Price, where 22 coal seams have been recorded. Theropod, hadrosaur, ceratopsian, pterosaur, bird and turtle tracks are common, along with the first frog tracks ever found from the Age of Dinosaurs.

Generations after dinosaurs were found in the Dinosaur Diamond, we know a lot more about these enduringly popular creatures and their tracks, but mysteries still remain. Pioneering paleontologists of our grandfather’s day could hardly have predicted that later trackers would find dinosaur freeways extending thousands of kilometers, where theropods whipped themselves into frenzies of sexual excitement during springtime courtship rituals. They likely would have been awed at the concept of a “Dinosaur Diamond,” connecting five dinosaur museums, each putting out online information at lightning speed. But some things they’d easily recognize are the bones, rocks and tracks that remain as tangible evidence of Earth’s treasures and prehistory.

Price’s Prehistoric Museum

The Prehistoric Museum in Price, Utah, the western point of the Dinosaur Diamond, now affiliated with Utah State University Eastern, was founded as a tourist attraction in the early 1960s with the acquisition of a complete Allosaurus replica for $2,250. Situated amid the Price-Helper coal mining district, the museum contains many tracks of hadrosaurs and ceratopsians extracted from the coal mines. The museum was expanded in the 1990s and now contains mounted skeletons of Utahraptor and ceratopsians.

Blanding’s Dinosaur Museum

The southernmost point of the Dinosaur Diamond, the Dinosaur Museum in Blanding, Utah, was founded in 1995 by the late Stephen Czerkas and his wife Sylvia, both renowned dinosaur artists. Stephen is famous for correcting ill-conceived reconstructions of dinosaurs like Stegosaurus and Diplodocus. The museum displays include a diverse array of Mesozoic animals exhibited as skeletons and as fleshed-out sculptures, many with feathers. The exhibits also contain tracks and a large number of historically significant artifacts related to dinosaurs and the media, including antique books, prints, famous paintings, sketches and movie props and posters.

The Quarry at Dinosaur National Monument

Dinosaur National Monument, the northernmost point of the Dinosaur Diamond, is centered on a large dinosaur quarry found in 1908 in the Morrison Formation near Jensen, Utah. It has historically been the most-visited dinosaur destination in the region. Most of Dinosaur National Monument extends east from the quarry for about 50 kilometers into remote Colorado terrain north of the small settlement of Dinosaur, Colo. The Utah Field House of Natural History State Park Museum is 19 kilometers west of the quarry, in Vernal, Utah. This museum was founded in the late 1940s and was greatly enlarged at a new site in 2004.
Dinosaur Journey in Fruita

The eastern point of the Dinosaur Diamond is demarcated by Dinosaur Journey in Fruita, Colo., one of three Museums of Western Colorado destinations dating back to the mid-1960s. The other two are the Museum of the West and Cross Orchards Historic Site, both in Grand Junction. Dinosaur Journey was established in Fruita, just west of Grand Junction, in 2000, and is located near important paleontological sites in the Morrison Formation, including Dinosaur Hill, Riggs Hill, the Fruita Paleontological Area and Rabbit Valley. The exhibits mostly contain dinosaurs and other reptiles from the Morrison Formation, as well as an assortment of Mesozoic tracks from the Western Slope region.

Moab Giants

Moab Giants is a new paleontological museum created in 2015 in Moab, Utah, in the heart of the Dinosaur Diamond. Moab Giants, a for-profit museum, was designed after the model of successful dinosaur museums in Poland at Baltów and Krasiejów, which have both outdoor and indoor components, as well as strong scientific underpinnings. Moab Giants is based on the theme of tracks, since so many spectacular tracks have been found in this region.

Moab Giants has a collection of local tracks of scientific interest, and a tradition of track research at partner scientific institutions like the Museums of Western Colorado and the University of Colorado. Five tracksites near Moab have been developed by the Bureau of Land Management as educational destinations also promoting research, interpretation and protection. This development has been based in large part on work done by scientists associated with Moab Giants and partner institutions, including the Museum of Moab and Utah Friends of Paleontology. The indoor Tracks Museum at Moab Giants includes exhibits that cover both local tracksites and others of global interest in Texas, New England, Poland and China. Electronic and traditional exhibits connect visitors to the local tracksite destinations on BLM land, and also to track collections online such as the 3,000 specimens at the University of Colorado.

But perhaps the best part of Moab Giants is the “PaleoSafari” trail, a kilometer-long open-air trail with about 130 full-sized reconstructions of dinosaurs based on the tracks and trackmakers of the Western Slope region.
Martin Lockley

Lockley is a professor emeritus of geology at the University of Colorado at Denver, and holds research appointments at other universities and museums in Colorado and Utah. He remains active in his search for tracks of dinosaurs, birds, pterosaurs and mammals, including human ancestors, in North America, China, Korea and other regions. He is author of more than a dozen books and 800 scientific articles and reports, mostly on fossil footprints.

http://www.earthmagazine.org/article/making-tracks-through-dinosaur-diamond