By the time that giant meteor collided with our planet at the end of the Cretaceous, some dinosaur species were already heading toward extinction, new research indicates.
Some dinosaur species were declining long before the 150-million-year-long Age of Dinosaurs ended, scientists find.
Apparently large herbivores such as Triceratops and the duck-billed dinosaurs saw a long-term decline before the catastrophe, but carnivores and other plant-eaters, such as giant sauropods, did not, researchers said. Why some dinosaurs were on their way out while others still thrived just before "the end" may have to do with their locations — whether they lived in North America or Asia, for instance.
The demise of all dinosaurs except birds came about 65 million years ago, when researchers think a giant meteor collided with Earth. Still, it was unclear if mass extinctions started gradually before the impact, perhaps due to volcanoes or other forces.
To explore this question further, vertebrate paleontologist Stephen Brusatte at the American Museum of Natural History in New York and his colleagues investigated seven major dinosaur groups during the end of the Cretaceous, encompassing nearly 150 species. Specifically, they analyzed the variability of the anatomy and body plans within those groups. Groups that show increasing diversity might have flourished in their environments and evolved into more species, while decreasing variability might be a warning sign of extinction in the long term.
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