Diggin' For Dinosaurs - Petrified Forest National Park
Though scientists have figured out what the now-petrified trees looked like, there's been considerable dispute over how they grew: in extensive forests or isolated stands, on dry uplands or wet bottomlands. The ideal place to view the current best guesses about the park's past is the Rainbow Forest Museum, which features murals and reconstructed skeletons and replicas of the creatures that lived among the trees. Even here, visualizing Triassic life is an exercise in the imagination, since the landscape was so different then. What is now an arid grassland, home to prairie dogs, rattlesnakes, and pronghorns, was once a lush forest with wide, braided river channels. Continental drift hadn't yet moved Arizona to its current position; instead it lay closer to the equator, at a low elevation. The climate was tropical, and the place may have looked something like the contemporary Amazon basin. The trees were different: giant conifers and thick-trunked, 30-foot-high horsetails flanked by cycads and tree ferns. It was a world of multihued greenery.
The animals, too, were unlike any found today. The museum displays the skeleton of an aetosaur, a long-bodied, short-legged herbivore with heavy armor plates and formidable shoulder spikes that made it look like it stemmed from the mind of a comic-book artist. Nearby is Placerias gigas, a heavy, sharp-beaked plant eater that in both size and stature resembled a rhinoceros. Perhaps most impressive, though, are two predators represented only by skulls. Metoposaurus was a huge amphibian - imagine a broad-bodied salamander 10 feet long, armed with razorlike teeth in a two-foot-long jaw. Next to it sits the skull of a phytosaur, a long, lean, large-toothed marine reptile that resembled, but is not closely related to, a crocodile. Phytosaurs grew up to 30 feet long and were the dominant predators in the ancient sloughs and swamps - lying in mud and water, only eyes and nostrils exposed, waiting to lunge at passing prey.
Formidable as phytosaurs were, they were on the way out. Within a short span of time they were superseded by animals represented here by a single partial skeleton and a reconstruction. The latter depicts Coelophysis, a nimble, carnivorous dinosaur whose bones have been found in the Painted Desert and elsewhere on the Colorado Plateau. The skeleton belongs to a small dinosaur named Chindesaurus. When it was excavated in the park in 1984, the specimen was dubbed Gertie, and with an estimated age of 220 million years, it was one of the world's earliest dinosaur fossils. Though older dinosaurs have since been found, palaeontologists agree that Gertie is part of the oldest known dinosaur family, the Herrerasauridae. The fast-moving, bipedal predator presaged the giant carnivores who would come to dominate the dinosaur world and captivate the human imagination.
It's not any single fossil animal, though, that makes Petrified Forest a site of global paleontological significance. Rather, it's the whole assemblage present here. Researchers have identified about 200 different ancient plant species, most of them from leaf imprints preserved in mudstone or from fossil pollen. They have found fossil fungus that was responsible for killing some of the trees. They have found fossilized sharks and lungfish, clams, snails, and even insects. They have found coprolites, or fossilized feces, of a number of animals, the examination of which can reveal what foods they ate.
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