Petrified Forest National Park - Dinosaur's Ancestors

Though the transformed trees are the most obvious and startling fossils that this part of the Painted Desert brings forth, they are not the only stone legacy from that distant time. Equally beautiful in their delicate way are the preserved replicas of leaves, seeds, cones, and fern fronds; equally dramatic are the long-entombed remains of animals, ranging from freshwater clams and fish to giant amphibians and reptiles, and including some of the earliest forerunners of the dinosaurs.

The masters of the swamps and waterways were the phytosaurs, crocodilelike creatures whose long slender snouts were studded with knife-sharp teeth. Averaging 12 to 20 feet in length (some exceeded 30 feet), they may have weighed several tons. Propelled by strong hind legs and powerful tails, they sculled through the swamps with only eyes and snorkeling nostrils exposed -- ever on the hunt.

Among their prey may have been salamanderlike metoposaurs, some of the largest amphibians of all time. These fish eaters were about 10 feet long and weighed up to half a ton, but their legs were very short; they probably wallowed in shallow water like the modern hippopotamus. They had massive skulls, often as long as two feet, equipped with needlelike teeth and large lower-jaw fangs.

The aetosaurs were heavily armored vegetarians -- a sort of reptilian armadillo -- whose large bodies made eating a full-time occupation. Covered with hard, protective plates, the creatures ranged from the size of a house cat to 15 feet long. Despite their armor plating, which sometimes included long shoulder spikes of rows of sharp spines along their sides, all must have been high-priority cuisine for the several kinds of great meat eaters that roamed the land.

Outstanding among these was the fast and fearful predator called Lythrodynastes, or "gore lord," the bane of the floodplain, with its horrendous claws and dagger-like teeth. Capable of walking on all fours or rearing up on its hind legs like the much later and larger tyrannosaurs, it was 14 to 20 feet long and weighed up to a ton.

Its largest prey was Placerias, an odd, three-eyed reptile that looked a bit like today's rhinoceros. The third eye on its forehead, less developed than the other two, was probably a simple light-sensing organ. Up to 12 feet long and weighing 2 to 3 tons, the ponderous barrel-shaped vegetarian traveled in herds and sported large tusks for digging up roots and plants.

Although many different kinds of long-vanished reptiles and amphibians have recently been found, and more are coming to light every year, complete skeletons are rare. In part, this is because the raging waters of the primal floodplain tore many of the bodies apart before they were buried, leaving the bones scattered and broken. Another reason is that the petrified bones, though they have endured for millions of centuries beneath the surface, last but a short time once they are exposed to the elements. The material of bones is replaced by a process that leaves them light and porous -- unlike the steel-hard petrified wood -- and they simply fall apart after a few rains. Even so, Petrified Forest is one of the world's best fossil locations from this period -- a wonderland where scientists can find the clues, preserved in fragile, powdery stone, that help them to solve the mysteries of ancient life.