In those days, the dinosaurs’ empire was in its infancy. (Halloween walking dinosaur suit)The evolutionary pioneers of the Dinosauria had to share this terrestrial realm with a host of short-legged and ugly reptiles, the beaked rhynchosaurs, the dog-faced cynodonts, and the dinosaurs’ own ancestral stock, the big-headed thecodonts. (Realistic dinosaur costume)This was the Triassic Period, the first of the three great Mesozoic ages. The next was the Jurassic, the Golden Age of Giants, when the dinosaur clans burst out of their Triassic limitations. Wave after wave of ever-larger species filled the land habitats—long-necked brontosaurs, grotesquely armored stegosaurs, and a complete array of bird-limbed predators from ten pounds to five tons in live weight.
At Como Bluff, the land was covered with warm ocean water, the Sundance Sea, alive with stout-shelled squid and porpoiselike fish lizards for most of the late Jurassic’s twenty million years. Above the Chugwater layers, the somber green-gray sandstones of the Sundance Formation enter this marine epoch in the stratigraphic chronicle. (Dinosaur costume)Butch Cassidy’s sidekick, the Sundance Kid, got his name from the same tiny Wyoming town that gave this Jurassic formation its formal geological nomenclature.
The waves of the Sundance Sea finally beat their last cadence 140 million years ago. But even now the rhythmic sea sound seems fresh, preserved in the ripple-marked sandstone surface and in the wave-winnowed piles of clam shells and fossil oysters, growing on top of each other, and the squid-pens known to the locals as “stone sea-gars.” Dinosaurs were not here. Their fossils rarely appear in ocean beds. But rocks the same age as Sundance in India and Australia provide skeletons, proof that the land ecosystem was firmly under the control of the dinosaurs all through Jurassic times. Sundance fossils and all the other rich Mesozoic marine beds underscore the one geographic limitation of the dinosaurs’ world.