miércoles, 20 de mayo de 2009
Chunks of petrified wood lay strewn in Arizona's Petrified Forest National Park. Most petrified trees here are of the species Araucarioxylon arizonicum, a towering conifer that grew in the humid, tropical lowlands of this region during the middle Triassic period, about 220 million years ago. Trees that fell here often landed in deep rivers, where they were quickly buried by sediment. Lack of oxygen inhibited decay, and heat and pressure over millennia turned the wood into solid quartz colored by impurities like iron, carbon, and manganese.
The rock that makes up the Sella Massif in northern Italy's Dolomites mountain range was once the floor of a shallow, tropical sea. This Triassic-era sea was home to massive coral reefs that built up over millions of years. More recently, glacial erosion carved the Dolomites into their dramatic crags and exposed the reefs and fossils that lay beneath
Ichthyosaurs were big-eyed, dolphin-shaped marine reptiles that lived during the Triassic, Jurassic, and Cretaceous periods. This specimen, uncovered in the hills of Guizhou Province, China, was an early species that had a rather reptilian look; later species took on a more fishlike form.
The mass extinction of the Permian period left a nearly blank slate for new plant and animal species to arise during the Triassic. Tree-like seed ferns, such as this fossilized Dicroidium found on South Island, New Zealand, developed during this period along with a variety of other flora, some of whose ancestors still exist today.
A carver in Guizhou Province, China, sculpts a Keichousaurus hui fossil, referred to locally as "sea dragons," into a chunk of stone. The remains of these diminutive Triassic-era reptiles and many others are prominent and well-preserved in this region—one small mountain rich in fossils has been dubbed "Lurking Dragon Hill." In China, the dragon is a symbol of good luck, and replicas like these help to curb illicit fossil collecting.
Ichthyosaurs, like this one found in Guizhou Province, China, evolved in the early Triassic, nearly 250 million years ago. Early specimens were reptilian in form—in fact, "ichthyosaur" means "fish-lizard"—but quickly evolved a dolphinlike shape. They went on to become one of the top ocean predators and thrived for 160 million years before going extinct in the mid-Cretaceous, about 25 million years before the dinosaurs died out.
This middle-Triassic reptile found in Switzerland measures only about 9 inches (23 centimeters) in length. Called Pachypleurosaurus edwardsi, these primitive amphibious reptiles were nothosaurs, among the first reptiles to venture into the shallow seas of the Triassic.
This Triassic-era fish is among the thousands of fossils uncovered in the mountains and karst formations of China's Guizhou Province. Much of this region was under a shallow ocean during the Triassic period, and sediments there teem with the ancient remains of fish, dinosaurs, and marine reptiles.
An artist's rendering shows hatchling nothosaurs heading for the safety of water as a hungry but terrestrial Ticinosuchus attacks near a lagoon in ancient Switzerland. Nothosaurs lived during the mid- and late Triassic period and were among the earliest reptiles to take to the sea. Because nothosaurs may have had to come ashore to lay eggs, the eggs and hatchlings would have been vulnerable to Ticinosuchus. Yet once the hatchlings reached deeper waters, they were safe—for the moment.
Artwork by DAMNFX