Early Jurassic Kayenta Formation from the Dinosaur Collector

   update 102912

This is a geologic layer in the Glen Canyon Group that is spread across the Colorado Plateau province of the United States, including northern Arizona, northwest Colorado, Nevada, and Utah. Desert conditions occurre as do occasional seasonal climate supporting ponds and lakes. It was situated in a climatic belt like that of Senegal with rainy summers and dry winters at the southern edge of a great desert. The influence of the desert increased as North America drifted northward into the arid desert belt. It has Dilophosaurus, small coelophysoids, sauropodomorphs, armored dinosaurs and small ornithischians. Fossils for of smaller forms are much less common that tracks would indicate. 

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Superficially, prosauropod grade sauropodomorphs look pretty much alike, so if you have a Plateosaurus in your toy series there isn't much incentive to do any other prosauropod figures. The Kayenta Formation is located in Arizona, and is one of the richest Early Jurassic formations in the Glen Canyon Group. The dinosaurs currently known from the formation are Dilophosaurus, Syntarsus, Ammosaurus, Scutellosaurus and Scelidosaurus.  Scelidosaurus was 14 feet long and shows similarities with Stegosaurus and Ankylosaurus, with bony plates down its back and a heavy body highest at the hips. Seven rows of bony studs and spikes were set into the skin on its back.

Coelophysids were the most sucessful theropods from the Triassic. The are the common small predators of the Early Jurassic and have been found world wide. Dilophosaurus at 20 feet was the largest and best known. The crest are found on it smaller relatives. Initially any large coelophysid with crests is assumed to be Dilophosaurus. More detailed fossils may show they are actually different members of the same family. Anchisaurus was a prosaurpod grade sauropodomorph and the largest herbivore. It had small feet but big hands with thumbs with formidable claws. The is evidence from South Africa that indicates the young were four footed but the adults were optionally bipedal.

Large crested therapods from the Early Jurassic found in various parts of the world are often attributed to Dilophosaurus.  Dilophosaurus had long, powerful legs, short arms, and 2 thin, highly arched crests on its head for display. Hundreds of small bony studs guarded the back of this primitive thyreophoran. Scutellosaurus walked on all fours but could also run on its hind legs, with a very long tail for balancing. It probably lived in an arid or semi-arid environment. Its teeth were serrated and leaf-shaped, and are generally free of signs of wear, suggesting that the animal did not chew its food before swallowing it.

Coelophysids survived from the Triassic and in the first part of the Jurassic were wide spread. They were small to medium size, fast running and preyed on smaller animals. Adult Anchisaurus the large herbivore of the Southwest United States were too large to be prey unless hunted by a pack. The young suropodomorphs would have been easy prey.