Fossil record scarcity may explain apparent dino decline pre-asteroid
A scarce fossil record may explain why many have long speculated that dinosaurs were already in decline before the asteroid collision 66 million years ago. A new study from UCL, published in Current Biology, analysed the fossil record in North America over the 18 million years prior to the asteroid impact.
The over 8,000 fossils suggest that the number of dinosaur species peaked around 75 million years ago, before declining over the nine million years leading up to the impact. But the team found that the trend may be due to fossils from that time being less likely to be discovered, likely due to fewer locations having exposed and accessible rock.
They looked at different dinosaur groups in North America, including herbivores and carnivores, adopting a technique used previously to estimate how likely species are to live in a particular area. They divided the continent into a grid and, based on the geology, geography, and climate of the time, estimated how many of these grid cells the different dinosaur types were likely to occupy at four different times over the last 18 million years of the Cretaceous period.
They found that the proportion of land occupied by the different groups likely remained constant overall. This suggests that their potential habitat area had remained stable, and they had a low risk of extinction.
“Dinosaurs were probably not inevitably doomed to extinction at the end of the Mesozoic,” Co-author Dr Alessandro Chiarenza (UCL Earth Sciences). “If it weren’t for that asteroid, they might still share this planet with mammals, lizards, and their surviving descendants: birds.”
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