The dinosaurs died quickly, snuffed out by the impact of an asteroid that sent a wall of fire and death racing across North America, an analysis of fossils found in Montana (USA) and North Dakota (USA) concludes.
The finding casts doubt on a theory that the dinosaurs died out slowly and that the asteroid impact was simply and end-the-misery trauma for an almost-vanished species. Peter M. Sheehan of the Milwaukee Public Museum was the first author of this study.
Researchers analyzed the number and distribution of fossils across large parts of the two states, where the animals roamed some 65 million years ago.
But William A. Clemens of the University of California at Berkeley said the Sheehan study fails to prove the asteroid theory of dinosaur extinction.
The remains of a 66 million-year-old dinosaur suggest that the extinct creatures were warm-blooded - not cold-blooded as was once believed - and capable of the swift and sustained motion typical of modern birds amd mammals.
A modern medical X-ray of a dinosaur fossil named Willo found clear evidence that the animal had four heart chambers that sent blood directly to and from the lungs and then pumped the oxygen-rich blood to the body through a single arched aorta, similar to how the human heart works.
"The single aorta is really important," said Dale A. Russell, senior research curator at the North Carolina Museum of Natural Sciences and a paleontologist at North Carolina State University. "This challenges some of the most fundamental theories about how and when dinosaurs evolved," Russell said.
Most reptiles have three-chambered hearts, but even in those with four chambers, the blood is pumped through double arteries that mix oxygen-heavy blood with oxygen-lean blood.
Cold-blooded reptiles are dependent on the environment for body heat. Warm-blooded mammals and birds generate their own body heat and are more tolerant of temperature extremes. Birds and mammals also have more physical endurance and can be swifter.
Some experts said discovery of the fossilized heart will change basic views about the dinosaur and send researchers scrambling to do more X-ray studies of intact specimens.
If verified by other studies that a rock-hard mass in the fossilized chest is a heart, it will mark the first time that scientists have been able to study the cardiac system of dinosaurs.
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