Palaeontology: Dinosaurs in decline before asteroid impact

Non-avian dinosaur species were in decline for approximately 10 million years prior to the mass extinction event caused by an asteroid impact, finds a new study published in Nature Communications. The research sheds further light on the extinction of dinosaurs.

The impact of a large asteroid at Chicxulub, Mexico is widely agreed to be responsible for the mass extinction of non-avian dinosaurs 66 million years ago. However, whether dinosaurs were in decline prior to the asteroid impact is debated, and it has been difficult to assess this using current fossil records.

Fabien Condamine and colleagues analysed 1,600 dinosaur fossils to assess speciation and extinction rates for six dinosaur families (Ankylosauridae, Ceratopsidae, Hadrosauridae, Dromaeosauridae, Troodontidae, and Tyrannosauridae). The authors found that the diversity of non-avian dinosaurs started declining around 76 million years ago. They suggest that this decline was linked to increased extinction rates in older species, which may indicate a lack of evolutionary novelty or that these dinosaurs could not adapt to the changing conditions. The authors also assessed ecological and physical factors in this shift and highlight that global climate cooling during the Late Cretaceous period (100 to 66 million years ago) may have contributed to dinosaur decline. They also indicate that a decline in the diversity of herbivorous dinosaurs, as a result of hadrosaurs outcompeting other species, may have played a role.

The authors conclude that the combination of these factors impeded the ability of dinosaurs to recover after the Chicxulub event and contributed to their extinction.