Some dinosaurs were declining before asteroid struck, say scientists (+video)
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.Skip to next paragraph
In Pictures Fearsome dinosaurs
Subscribe Today to the Monitor
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.
"People often think of dinosaurs as being monolithic — we say, 'The dinosaurs did this, and the dinosaurs did that,'" said researcher Richard Butler of Ludwig Maximilian University in Munich. "But dinosaurs were hugely diverse. There were hundreds of species living in the Late Cretaceous, and these differed enormously in diet, shape and size. Different groups were probably evolving in different ways and the results of our study show that very clearly."
The scientists found that biodiversity of large herbivores, including the duck-billed hadrosaur dinosaurs and horned ceratopsid dinosaurs such as Triceratops, seemingly experienced a long-term decline during the last 12 million years of the Age of Dinosaurs. In contrast, a number of other dinosaurs stayed relatively stable or even may have slightly increased in biodiversity, including carnivores such as tyrannosaurs, mid-size herbivores such as the armored ankylosaurs and bone-headed pachycephalosaurs, and truly enormous herbivores, such as sauropods, that gulped their food whole.
The picture of dinosaur biodiversity grows even more complex if one takes different locations into account. Although hadrosaurs apparently declined in North America, their diversity was increasing in Asia during the late Cretaceous. (The Cretaceous Period, which lasted from about 145 million to 65 million years ago, was the last part of the Age of Dinosaurs.) [Dinosaur Detective: Find Out What You Really Know]