Word: triassic
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...nature was setting the stage not only for dinosaurs but also for the age of mammals that followed--and the eventual rise of the human species. Says Shubin: "If you look at the major groups of animals in the world today--mammals, crocodiles, turtles, frogs--most appeared during the Triassic, 220 million to 200 million years ago." With new discoveries making the origin of these groups ever more remote, he adds, "any find dating to this period is clearly very crucial...
During the Triassic period -- say, 225 million years ago -- it would have seemed absurd to suggest that dinosaurs would soon inherit the earth. At the time, they were inconsequential creatures, perhaps the size of dogs, living among far more imposing giant crocodiles and other reptiles. During Triassic times, the continents were stuck together in a single mass that scientists call Pangaea. The planet was warmer and rainier than it is today -- ideal conditions for the growth of vast forests along coastlines and adjacent to rivers. Conifers, horsetails, tree ferns and ginkgos were the dominant vegetation. Giant 3-ft. dragonflies whirred...
...reason, he and many colleagues believe, may have been a mass extinction of many of the planet's species late in the Triassic period. It could have been caused by the impact of a massive asteroid or comet, perhaps, or by dramatic climate changes triggered as Pangaea separated to form distinct continents. As other animals disappeared wholesale, the dinosaurs evolved rapidly to fill vacant ecological niches. Says Sereno: "It's very difficult to argue that the dinosaurs had something the others didn't. Instead of evolving because they were better, maybe they evolved because there was a sudden vacuum...
Excavations at the Nova Scotia site have so far yielded more than 100,000 fossilized bone fragments, all dating from shortly after the mass extinction some 200 million years ago that marked the end of the Triassic period and the beginning of the Jurassic. Because of some rapid change, perhaps a catastrophic event, the fossil record shows, 43% of the animal families whose fossilized remains are found in the older Triassic rock are missing from the Jurassic layers just above it. The sudden mass extinction opened the evolutionary way for the proliferation of the dinosaurs and the emergence...
...Triassic-Jurassic extinction, however, that evidence may exist. Less than 500 miles northwest of the Nova Scotia fossil find is the enormous Manicouagan impact crater, its outermost ring--clearly visible in satellite photographs--measuring more than 90 miles in diameter. Given the margins of error in dating, the age of the crater (about 214 million years) makes it suspect in the 200 million-year-old extinction...