Some dinosaur groups experienced a long-term decline before their extinction 65 million years ago reports a study published in Nature Communications this week. It is thought that dinosaurs became extinct at the end of the Cretaceous period due to volcanism and a bolide impact, but whether this event reached them in their prime has been unclear. This study provides evidence that suggests that at least some groups of non-avian dinosaurs were experiencing a decline before the extinction event.
Stephen Brusatte and colleagues calculated the variability in anatomy and body plans of seven major dinosaur subgroups during the Late Cretaceous at global and regional scales to reveal increases or decreases in biodiversity. Results show that the numbers of large-bodied bulk-feeding herbivores, such as ceratopsids and hadrosauroids, were in decline during the final stages of the Cretaceous. Data for carnivorous dinosaurs and mid-sized herbivores did not show this trend.
These findings show that the evolution of dinosaurs during the Late Cretaceous was complex and no universal biodiversity trend can be seen. The data suggests, however, that at least some dinosaur groups did endure a long-term decline in morphological variability before their final extinction.