65 million years ago, dinosaurs experienced bad weather and an asteroid impact, but scientists say their real problem was too many males for the number of females. They think that the sex of dinosaurs, like crocodiles today, depended on the temperature the day they were born. Debris from the asteroid impact blocked the sun and cooled down the climate, leading to the birth of too many males.
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Most scientists now believe that, due to the fossil evidence, birds are an evolutionary offspring of dinosaurs. Now they’ve discovered that 175 to 275 million years ago, when this evolution began to take place, oxygen fell to dangerously low levels on Earth. This may have led to the major extinction event which eliminated 90% of all the species. It would have made breathing the air at sea level the same as breathing at high altitudes today and could have led to the development of the unusual breathing system found in some dinosaurs, including the brontosaurus, which still exists in today’s birds.
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University of Arizona senior Greg Cranwell was walking on campus when, he says, “I was looking down at the flagstone and thought I saw something. I was unsure but I thought ‘what’s it going to hurt if I just look?'” He found he was walking on 270 million-year-old footprints. He says, “I ran to the campus president and told her that we needed to get this thing out immediately and she said that with a little more convincing she would have the slab pulled.”
Ashley Nowe writes in the Arizona Daily Wildcat that Cranwell spent hours looking at photographs of the ancient footprints, comparing them with documented fossil tracks. “It was like comparing apples and oranges,” he says. “It doesn’t take a genius to know if the prints match or not.”
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Poor dinosaurs?their time really was up. Scientists now think that cold was killing them off long before that asteroid wiped them out 65 million years ago. Half of all dinosaurs were gone by then and the impact was just the final straw.
Fossil evidence from the Drumheller valley in Alberta, Canada, laid down 7 million years before the asteroid hit, shows that average temperatures had dropped enough to kill off cold-blooded reptiles such as crocodiles, turtles and dinosaurs. Oxygen isotope readings from fossils show the temperatures at which they formed, so scientists can track climate change over time.
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