14 DAY TRIAL // A new investigation demonstrates that large, herbivore dinosaurs were declining even before the Cretaceous-Paleogene (K-T) extinction event, some 65.5 million years ago. The same research indicates that mid-sized herbivore and carnivore dinosaurs were doing just fine before they died off.
Scientists have been trying to figure out whether the asteroid that is believed to have killed off the giant lizards destroyed flourishing species, or declining ones. The answer is not simple, the new study found.
Experts from the American Museum of Natural History (AMNH) say that large-bodied, bulk-feeding herbivores were indeed declining during the Cretaceous Period. This decline began around 12 million years before the K-T event occurred.
At the same time, carnivores were flourishing, as were mid-sized herbivores. However, the team cautions that it's important to take into account the geographical location of each dinosaur population when making any sort of assessment about their biological success.
Details of their study were published in the May 1 issue of the top journal Nature Communications. “Few issues in the history of paleontology have fueled as much research and popular fascination as the extinction of non-avian dinosaurs,” lead study author Steve Brusatte explains.
“Did sudden volcanic eruptions or an asteroid impact strike down dinosaurs during their prime? We found that it was probably much more complex than that, and maybe not the sudden catastrophe that is often portrayed,” adds the Columbia University graduate student.
Brusatte is also associated with the AMNH Division of Paleontology. The chair of the Division, Mark Norell, expert Richard Butler from the Ludwig Maximilian University and scientist Albert Prieto-Márquez from the Bavarian State Collection for Palaeontology, were also members of the team.
The researchers analyzed the extinction of dinosaurs based on the variability of body structure within particular groups of dinosaurs, a factor called morphological disparity. Most other investigations were conducted based on estimates of how many species of dinosaurs lived at any given time.
“By looking just at trends in taxonomic diversity, you get conflicting answers about the state of dinosaurs prior to extinction. This is because the results can be biased by uneven sampling of the fossil record,” Brusatte explains, quoted by Astrobiology Magazine.
“In places where more rock and fossils were formed, like in America's Great Plains, you'll find more species. We wanted to go beyond a simple species count for this study,” he concludes.