Dinosaurs and the Desert
Where and When Did They Live
by Joe Zentner
The Southwest is rich with evidence about a time when dinosaurs ruled the land. Across the region in California, Utah, Colorado, New Mexico and Arizona you can visit museum exhibits about dinosaurs and in some areas, sites with dinosaur fossils.
Dinosaurs in the Desert
Many scientists believe that dinosaurs were both numerous and varied in what is now called California during the Mesozoic Era. Recent discoveries are beginning to challenge the notion that few dinosaurs lived along the Pacific Coast.
California’s dinosaurs would have lived in a violent world where volcanic eruptions continuously shook the land, darkening the sky with ash and sending steaming mudflows surging through canyons. It was among majestic volcanoes, in a world that harbored a fascinating array of plants and animals, that California’s dinosaurs would have flourished.
Still, few dinosaur remains have been found in California. During Triassic and Jurassic times, much of California was under water. Dinosaurs were land-dwelling animals; consequently, the infrequent dinosaur fossils found in the state probably originated to the east and were washed out to the ocean where they were deposited on the sea floor. Retreating seas and coastal uplifting created the land that was to become California. Weathering and erosion then exposed buried fossils.
Dinosaur fossils found in Arizona include Ammosaurus, Anchisaurus, Anomoepus, Chindesaurus, Coelophysis, Massospondylus, Navahopus, Revueltosaurus, Rioarribasaurus, Scutellosaurus, Segisaurus, Sonorasaurus, and Syntarsus.
Dinosaurs lived in New Mexico between 225 and 66 million years ago. The state is unique in that it preserves both body fossils and trace fossils of Triassic, Jurassic and Cretaceous creatures. Body fossils reflect actual pieces of an animal, for example, bones and teeth. Trace fossils are “fossilized behavior” and can include footprints, skin impressions and egg shells. Dinosaur fossils have been found across all of New Mexico except for the southeastern corner of the state.
Late Cretaceous dinosaurs from the San Juan Basin were some of the last to have lived on Earth. They are well known because of the information they have provided scientists about the cause(s) of dinosaur extinction.
New Mexico’s record of Triassic dinosaurs includes skeletons of Coelophysis, teeth of Revueltosaurus, bones of Eucoelophysis, fragmentary skeletons of other dinosaurs and tracks of many dinosaurs. The fossil record is particularly significant because some of these dinosaurs are among the oldest known in the world. Additionally, Coelophysis, the official state fossil, is one of the best-preserved dinosaurs in terms of both completeness and abundance.
New Mexico’s best-known dinosaur fossils come from 75 to 66 million-year-old rocks in the San Juan Basin of the northwestern part of the state. Late Cretaceous fossils are particularly abundant in the Bisti-De-na-zin Federal Wilderness Areas south of Farmington. Late Cretaceous dinosaurs from the San Juan Basin lived in river floodplains and jungles located near a seacoast.
On March 17, 2004, clear imprints of the heel, pelvis, tail and shuffling feet of a dinosaur were unearthed at the St. George, Utah, Dinosaur Discovery Site at Johnson Farm, providing paleontologists with the first evidence of a “squatting dinosaur.” James Kirkland, the Utah State paleontologist, observed that the new discovery suggests the creature rested on its hind end and put its hands down, with claws curled inward, giving scientists new insight into how dinosaurs used their hands. It may have shuffled forward before walking away, while dragging its tail.
In Early Jurassic times, a shallow lake stretching hundreds of miles existed in what is today southwestern Utah. Dinosaurs congregated on the shores of this lake. They may have crouched there on the shores after eating fish or plants. Since Sheldon Johnson’s initial track discovery at the St. George Site in 2000, this locale has grown into North America’s largest site for Early Jurassic footprints.
Many of the tracks are well preserved at the bottom of a three-foot-thick layer of sandstone and belong to the track name Eubrontes, meaning three-toed footprints. They include examples of footpads, claw marks and detailed skin impressions. To promote paleontology, the Johnson family donated the initial dinosaur tracks to the city of St. George, Utah, which then purchased the land and began constructing an interpretive center in the summer of 2004.
New Information About Dinosaurs
Scientists are continuing to learn more about dinosaurs. For instance, paleontologists digging in the Patagonian wilderness of Argentina recently reported finding the remains of a meat-eating dinosaur that was perhaps clever enough to bring down its prey by hunting in packs. Researchers suggest that by working together, these dinosaurs may have been able to kill animals much bigger than they were, including the 125-foot-long, 100-ton Argentinosaur, the plant-eating behemoth that may have been the largest land animal that ever lived.
Paleontologist Philip Currie of Canada’s University of Alberta points out that the Argentine deposit held the remains of at least seven animals ranging from 18 to 40 feet long, suggesting they may have been a herd or family in which different group members could provide either speed or strength.
The study of dinosaurs in the desert Southwest and elsewhere stretches our imaginations, gives us new perspectives on time and space, and invites people to discover worlds that are very different from our modern Earth. From a scientific point of view, the study of dinosaurs is important both for understanding the causes of past major extinctions of land animals as well as for understanding changes in biological diversity caused by previous geological and climatic changes on Earth. The wealth of new information about dinosaurs acquired over the past 30 years has challenged forever the age-old perception of dinosaurs as being slow, clumsy, dim-witted beasts.
Questions and Answers
Q. Why are dinosaurs called “dinosaurs”?
A. Paleontologist Sir Richard Owen coined the word dinosaur (meaning “fearful great lizard”) in 1842. Over time, the term was simplified to “terrible lizard.” Not all dinosaurs, however, were terrible. Nor were they all lizards.
Q. Why were dinosaurs so big?
A. Most dinosaurs weren’t giants, but no one knows for certain why some were so huge. The largest known dinosaur is called Argentinosaur, the smallest, Compsognathus.
Q. What did dinosaurs eat?
A. Some dinosaurs ate lizards, turtles, eggs or early mammals. Some hunted other dinosaurs or scavenged on dead animals. Most, however, ate plants (but not grass, which hadn’t evolved yet). Rocks that contain dinosaur bones also contain fossil pollen and spores, which indicate the many different plants that existed during the Mesozoic Era. Many of these plants had edible leaves and, in the latter part of the dinosaur age, fruit. Although the exact time of origin for flowering plants is uncertain, the last of the dinosaurs almost certainly had fruit to eat.
Q. What colors were dinosaurs?
A. Direct fossil evidence for dinosaur skin color is unknown. Some dinosaurs likely had protective coloration, such as pale undersides to reduce shadows, as well as irregular color patterns to help camouflage the creatures in vegetation. Some dinosaurs may have been as brightly colored as modern-day lizards, snakes and birds.
Q. How long were dinosaurs around?
A. They evolved about 228 million years ago (during the Triassic Period, toward the beginning of the Mesozoic Era) and became extinct some 65 million years ago at the end of the Cretaceous Period. Eoraptor is the earliest known dinosaur. But because Eoraptor’s skeleton shows some genetically advanced skeletal features, older dinosaur fossils may yet be found.
Q. Did all dinosaurs live together, and at the same time?
A. No and no. Both time and geography separated dinosaur communities. The “Age of Dinosaurs” (the Mesozoic Era) included three consecutive geologic time periods (Triassic, Jurassic and Cretaceous). Different dinosaur species lived during each of these three periods. For example, the principal Jurassic dinosaur Stegosaurus already had been extinct for some 80 million years before the appearance of the Cretaceous dinosaur known as Tyrannosaurus. At the beginning of dinosaur history (the Triassic Period), there was one supercontinent on Earth, known as Panagea. Many dinosaur types were widespread across it. However, as Panagea broke apart, dinosaurs became scattered across the globe on separate continents, and new dinosaur types evolved separately in each geographic area.
Q. Are all fossil animals dinosaurs?
A. No. Dinos were a group of ancient reptiles that had distinctive skeletal features. The hips, hind legs and ankles were specialized and allowed the legs to move directly under the body rather than extending out from the side of the body as in modern lizards. This arrangement enabled dinosaurs to bring their knees and ankles directly below their hips and provided the necessary attachments for very strong leg muscles. Dinosaur bone structures were well designed for supporting a large body, for standing upright and for running. The front legs were well adapted for grasping prey. These skeletal features separated dinosaurs from other ancient reptiles, such as the plesiosaurs and pterosaurs, and certainly from the much more recent saber-tooth tigers, mastodons, mammoths and other Ice Age animals. The fastest dinosaurs probably weren’t any more speedy than modern-day land animals. Dinosaur speeds are deduced from fossilized trackway finds and the dinosaurs’ shape and structure. The speediest dinosaurs more than likely were bird-like bipedal carnivores called theropods, which had long, slim hind limbs and light bodies.
Q. Where are most dinosaur fossils found?
A. Fossils have been found all over the world and on every continent (except for Antarctica). Large concentrations have been found where it is easiest to recover fossils; that is, where Mesozoic Era sediment is exposed, such as some of the badlands. In North America, huge numbers of dinosaurs have been found in the Western Rockies, as well as in Alberta, Montana and the Southwest.
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