Some dinosaurs were declining before asteroid struck, say scientists (+video)
"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]