A recent study shows that larger herbivorous dinosaurs were becoming less diverse before the mass extinction.
Scientists believe a giant meteor collided with the Earth 65 million years ago, putting an end to the dinosaurs' reign. Ongoing volcanism and significant sea level changes on the planet at that time likely also contributed to the large reptiles' disappearances.
Though all the dinosaurs (except birds) were wiped out by these massive climate changes, a new study shows that some species were already in decline.
"People often think of dinosaurs as being monolithic — we say, 'The dinosaurs did this, and the dinosaurs did that,'" Richard Butler, one of the study's authors from Ludwig Maximilian University in Munich, told LiveScience. "But dinosaurs were hugely diverse."
Butler and his co-authors studied the varieties of body structures present within about 150 different species of dinosaurs. The more variability within a species, the more robust its population probably was.
The new research indicates that trends in biodiversity were not universal among all dinosaur groups before their extinction.
Large-bodied, heavy-feeding herbivores were already losing ground during the late Cretaceous period, before their mass die-off.