Scientists have debated a tantalizing question for decades: Were dinosaurs already on the decline before the catastrophic asteroid impact 66 million years ago? At first glance, the fossil record tells a story of dwindling dinosaur species leading up to the asteroid event.
However, a new study by University College London (UCL) researchers challenges that narrative by uncovering a hidden factor—gaps and biases in the fossil record itself.
The study focuses on North America, examining 8,000 dinosaur fossils from 18 million years before the asteroid struck. On the surface, the data suggest a peak in dinosaur diversity 75 million years ago, followed by a decline over the next nine million years.
However, lead author Dr. Chris Dean and his team delved deeper, employing advanced techniques to determine if this trend was real or just an illusion caused by an incomplete record.
Using a method called occupancy modeling—commonly used in biodiversity studies—they analyzed four major dinosaur groups: Ankylosauridae (armored dinosaurs like Ankylosaurus), Ceratopsidae (three-horned giants like Triceratops), Hadrosauridae (duck-billed dinosaurs like Edmontosaurus), and Tyrannosauridae (carnivores like T. Rex).
The asteroid that doomed the dinosaurs struck Earth at the ‘deadliest possible’ angle
By dividing North America into a grid and factoring in ancient geology, geography, and climate, they estimated the likelihood of dinosaurs living in a given area and the chances of their fossils being detected.
Their findings? While dinosaurs likely occupied stable habitats, the odds of detecting their fossils declined significantly in the final six million years before the asteroid. This was due to the shrinking exposure of fossil-rich rock layers, driven by geological changes like mountain uplift and sea-level retreats.
The team concluded that dinosaurs’ seeming “decline” was more a reflection of this reduced sampling window than actual species extinction.
Interestingly, not all dinosaurs faced the same fate in the fossil record.
Ceratopsians, such as Triceratops, thrived in plains away from rivers, habitats better preserved in the rock formations of that era. As a result, their fossils are more common and offer a glimpse of species diversity that may have been underestimated in other groups.
Co-author Dr. Alessandro Chiarenza highlighted the implications: “If we take the fossil record at face value, dinosaurs might seem doomed before the asteroid. But our findings suggest they were likely holding steady, and their extinction was not inevitable.”
This study reshapes our understanding of dinosaurs’ final chapters, emphasizing that the story isn’t just about what the fossils tell us and what they leave out.
Journal Reference:
- Christopher D. Dean, Alfio Alessandro Chiarenza, Jeffrey Doser et al. The structure of the end-Cretaceous dinosaur fossil record in North America. Current Biology. DOI: 10.1016/j.cub.2025.03.025
Source: Tech Explorist
