While the legacy of the dinosaurs endures in our fine-feathered friends, the former glory of the Mesozoic era is long gone. Young children learn about the sad fate of the dinosaurs delivered by an asteroid, a dramatic extinction event for one of the more charismatic creatures that have ever lived. However, the asteroid may have had an accomplice. A recent study published in Proceedings of the National Academies of Sciences concludes that the dinosaurs were already standing on shaky ground, threatened by a harsh environment and decreasing genetic diversity.
The idea that the dinosaurs suffered under harsh conditions prior to the asteroid impact is not novel. Scientists have previously proposed that extensive volcanic activity and climate change negatively affected the well-being of organisms in the late Cretaceous. The recent study proposes a new cause of weakened dinosaur resilience: genetic stagnation. “New species weren’t being produced as fast as species were going extinct,” says Manabu Sakamoto, lead author of the study and paleontologist at the University of Reading. “That made the dinosaurs vulnerable to drastic environmental changes—especially something like an apocalypse.”
Sakamoto and his team identified a significant decrease in dinosaur evolution through a review of prior work on paleo-taxonomy. “Previous studies were quite simple,” says Sakamoto. “They counted the number of [dinosaur] species around at each age or time interval to see which ones were peaking or troughing when, to be honest, it’s not a very statistical approach.” The team analyzed this data to measure the number of speciation events in which new species emerged. Their research demonstrates a sharp decline in speciation events starting in the mid-Cretaceous. This era was marked by extraordinary changes, including the dissolution of Pangea, explosive volcanic activity, and significant global cooling.
Sakamoto suggests that the conditions on Earth 70 million years ago may offer a grim glimpse into the future. “We live in a world where we face unprecedented levels of extinction almost daily,” Sakamoto said. “If we are going by the example of dinosaurs, it might mean were are priming our world for a mass of extinction, given some kind of a catastrophic event. By inferring things that happened in the past, we can say something about our own future.”