208-144 MillionYears Ago
The Glen Canyon Group

Wingate Formation

The Wingate Formation is about 300ft thick in the area of Canyonlands, and lies conformably atop the Chinle Formation. The Wingate, like most of the Glen Canyon Group, is composed of typical eolian deposits, including fossil dunes and small playa or oasis deposits. The most common track type in the Wingate are small theropod Grallator tracks, typically 15-20cm long. These are about "twice the size of the diminutive, yet abundant, Grallator tracks found in the upper part of the Chinle Group." Based on a formula which relates foot length to hip height, these Grallator track makers were probably about 3-4 ft tall at the hips. Near the top of the Wingate Formation, larger theropod tracks, Eubrontes (up to 35-40cm long) are known. Eubrontes tracks are about twice the size of Grallator. Lockley and Hunt notes that "in contrast with the underlying Chinle Group, in which dinosaurs were few and other kinds of archosaurs were many, the Wingate evidence suggests a vertebrate community dominated by bipedal theropod dinosaurs. The pronounced earliest Jurassic dinosaur radiation is thus, in our view, showing up clearly in the track record"
Kayenta Formation
The Kayenta is a thin layer (about 200-600ft) of weakly inclined river sandstone, sandwiched between two massive windblown, dune sandstones, the Kayenta and the Navajo. The Kayenta preserves both dinosaur fossils (such as Dilophosaurus) and footprints, as well as the fossils of the mammal-like reptile tritylodont.
Vertebrate footprints attributed to therapod dinosaurs are dominant by Kayenta time. Some of the Kayenta dinosaur tracks are very small and bird-like, such as Anomoepus, with relatively slender, widely-splayed digits, and "pigeon-toed," inwardly rotated tracks. Most scientists attribute Anomoepus to ornithopod theropods rather than early birds because Anomoepus tracks found in late-Triassic/early-Jurassic strata of the Connecticut Valley "occasionally show five-toed front footprints, as well as heel (metatarsal) and pelvic impressions.
During the Jurassic a mountain range, the Sevier orogenic belt, extended from western Mexico up through the length of eastern California, Oregon, Washington and northward into western Canada. Almost parallel to his, a fold and thrust belt stretched from eastern Nevada northward to Montana and into Canada. A downwardly warping, or subsiding crustal area called the Chihuahua trough developed in the Jurassic within extreme southeast Arizona. The Late Jurassic (140-160 million years ago) saw sedimentation flow eastward from the Sevier belt of California-Nevada into a vast oceanic trench within the western states including northeast Arizona. Once lifted above sea level and drained, later accumulations of river sediments resulted in the famous Morrison Formation which is now seen as a series of shales, siltstones and sandstones. The Jurassic Period, the second period of the Mesozoic, was a time during which dinosaur populations expanded, diversified and flourished. It was also a time when being big, at least for many dinosaurs, was good additional insurance for survival in a world filled with giants. Revolutionary changes in both habitats and life forms followed the preceding Triassic Period and the scenery would never be the same.
Geology and fossils of Glen Canyon Time
The Glen Canyon Group is divided into four distinct sedimentary formations. The Wingate Sandstone at the bottom of the group is the oldest of these units followed by the Moenave, Kayenta and Navajo Sandstone Formations. Both the Moenave and Kayenta Formations were deposited by river action, likely on the margins of very harsh, vast Sahara Desert-like environments.
These deep pure quartz sand dunes cover an immense part of what is northeastern Arizona and neighboring states. The Navajo Sandstone itself represents one of the most massive sand deserts ever to have existed on earth!
The Moenave and Kayenta Formations indicate conditions alternating between dry windblown dune desert and wet lowland river and swamp environments. Reasons for such unprecedented sand accumulations being interrupted by seemingly opposite wet lowland conditions represent long episodes of severe seasonality. During harsh, hot climatic conditions, silica-rich lowland clays may have physically broken down and were swept into dunes by off shore winds. In more modern times, and to a much lesser extent, such conditions appear to have been responsible for the resource decline and disappearance of large human civilizations in North Africa and Peru.
WINGATE SANDSTONE FORMATION
Dinosaur and other fossils occur in all of the Glen Canyon rocks to one extent or another. Phytosaurs apparently continue to be one of the dominant quadrupeds in the Upper Triassic Units though their fossils are rare in the Wingate Sandstone and are usually found only as fragmentary teeth and bones in gravel bar river conglomerates. Trackways of reptiles and insects are however very common on old dune surfaces of the Wingate Formation and provide good evidence that the dunes supported a surprising animal population.
MOENAVE FORMATION
By the time the Moenave Formation was being deposited, conditions were right for better fossil preservation. Bones of three-foot long primitive crocodiles called Protosuchus are found in the Dinosaur Canyon Member of the Moenave Formation seen along the Vermillion Cliffs on the east side of the Colorado River. Protosuchus was clearly different than the phytosaurs which shared similar habitats. These early crocodiles had broad, flat heads, strong limbs, and bony armor scutes along the belly. Theirs was an evolutionary success story because the crocodilians, even though they became much more advanced than Protosuchus, are still with us today. A rare tritylodont mammal-like reptile is also known from the Moenave Formation, and like the first crocodiles, very primitive mammals (or very advanced reptiles) would find themselves sharing not only the final years of the Triassic with the dinosaurs, but for millions of years to primitive until the close of the Mesozic Age of Reptiles.
FOSSIL TRACKS IN THE MOENAVE
A rare occurrence of running dinosaurs has recently been documented in the Moenave Formation near Cameron, Arizona, dating from the Early Jurassic, about 180 million years ago The tracks show strides of 16 feet and an estimated speed of 20 miles per hour. These tracks probably belonged to Dilophosaurus, which is the first large carnivorous dinosaur known to appear anywhere in the fossil record, and may be closely related to the generalized megalosaurs found worldwide.
There are at least 34 dinosaur trails (over 300 tracks) in this location with a total of three other running dinosaur tracks. The speeds of the three small trackways are estimated to be from 8-14 miles per hour. All of the footprints are thought to be made by small theropods (meat-eating dinosaurs), possibly including Syntarsus, Coelophysis and Segisaurus. This amazing tracksite was actually first discovered in the 1930's by the famed Roland T. Bird, who was told about it by an elderly Navajo man describing giant "bird" tracks in the desert. Bird made no map of the site but did have a photograph taken of himself knelling next to the tracks. The site was long lost for the ensuring 50 years until Scott Madsen, working as a preparator at the Museum of Northern Arizona, studied the photo and went out into he general area east of Cameron the Navajo reservation in 1986. After driving around for several days, he recognized the landmarks from the photo and indeed the site was found. The Cameron site is one of six documented Early Jurassic tracksites that are known to exist in northeast Arizona. Permission from the Navajo Nation is always required before accessing their land.
The environment of the Wingate Sandstone phase of the Moenave Formation was probably hot and dry with occasional period of river deposition to form the Moenave. Various tracks found over the years in the Kayenta have been given dinosaurs name such as Coelophysis, Dilophosaurus, Eubrontes, Anchisauripus, Grallator, Kayentapus, Hopiichnus, Navahopus, Megalosaurus, Syntarsus and Scutellosaurus though some of these names, based on tracks, may not be entirely valid.
The study and interpretation of trackways has great potential but in recent years scientists realized that the identification of dinosaur species on the basis of footprints isn't always an exacting science. Often, such have entirely different Latin names than the dinosaurs that may have actually left them so long ago and it is only when the intact fossilized feet of these rare dinosaurs are found that correct matches can be made.
Tracks can give us a wealth of information pertaining to classification, speed and type of locomotion, posture, social behavior (e.g. herding), recognition of ancient environments, shoreline identification, depth of water, and evolution of these reptiles. For instance, all dinosaur tracks indicate no "tail dragging" marks, inferring that the dinosaurs indeed did walk with an upright posture. Also, the fact that there are many, many more tracks than bones available for study increases the urgency of learning to understand what tracks can tell us.
Paleontologist T. Bird described a badly trampled area as: ... a 'chicken yard' hodge-podge of footprints, few of which can be identified as belonging to a trackway ... a single trackway shows about 10 footprints in a row heading west-the only animal that seemed to know where he was going." Many sites show dinosaur tracks distributed at random representing many different animals crossing one spot but maybe at different times. Sometimes the tracks are uniform, and represent a single species of dinosaur, either individually or in groups.
KAYENTA FORMATION
Dinosaur tracks are common on siltstone slabs that have been broken loose from Kayenta Formation strata. Three toed tracks and bones of ceratosaurs and the therapod Dilophosaurus are typical in these rocks. Dinosaur finds include two sites in which mass burials of Syntarsus kayentakatae and Dilophosaurus wetherilli are known, as well as bones from the primitive ornithischian Scutellosaurus and the early prosauropod Massospondylus Fossil remains of Dilophosaurus in the Kayenta occur 50 feet above the fossils of the early crocodile Protosuchus. Interestingly, it is speculated that Dilophosaurus was somewhat dependent on water for buoyancy because of having a weaker hip structure than other large meat-eaters.
No other anatomical feature of the Dilophosaurus skeleton however, seems to reinforce this aquatic view. Additionally, debate surrounds the use and even anatomical placement of two thin structures that have been restored as crests on the dilophosaur's skull, and its poorly fused snout. Both features are structurally weak. Perhaps Dilophosaurus, despite its fearsome appearance, was a scavenger, content with scaring off its predators and picking up the pieces after someone else made the actual kill. If Dilophosaurus indeed had crests were they used in sexual display? Was it a fish eater? More evidence is needed to answer these questions.
MASSOSPONDYLUS "Massive Vertebra"
Massospondylus was an early herbivore about 13 feet (4 m) long and 3 feet (1 m) tall. It had a long neck, very long tail, a small head, peg-like teeth, and large, five-fingered hands with a large thumb claw. Massospondylus may have been able to use its hand for grasping in addition to walking. Its back legs were only a little bit larger than its front legs. It was a very common dinosaur.
Massospondylus lived about 205 to 194 million years ago, during the early Jurassic period. It was an herbivore, a plant eater. It swallowed pebbles and small stones to help in the digestion of the tough leaves and other plant material that it ate. These gizzard stones (gastroliths) would help grind up the food in the stomach. Gastroliths have been found in Massospondylus fossils. Massospondylus walked on four muscular legs and was a relatively fast runner. It may have also run on two legs. Dinosaur speeds are estimated using their morphology (characteristics like leg length and estimated body mass) and fossilized trackways.