What would have happened if the infamous Chicxulub asteroid had just whizzed by Earth? Would you now be able to Instagram a Brontonsaurus sighting or a T. Rex storming the Empire State Building? The answer is: probably not.
There is no question that the asteroid was the final doom of the dinosaurs 66 million years ago. However, Fabien Condamine, a research scientist at the French National Center for Scientific Research who just contributed to a new study published in Nature Communications, believes that dinos could have started going extinct as far back as 70 million years ago. Earth began to cool. Herbivores began to die off, probably because the plants they ate could not survive the drop in temperature, and their carnivorous predators went with them.
“The asteroid impact was a kind of 'coup de grâce' that would have ended the dinosaur reign,” Condamine tells SYFY WIRE. “We further pinpoint the failure of dinosaurs to adapt to a changing environment, and then their inability to recover from the cataclysmic asteroid impact. It seems that the dinosaurs were no longer adapted to the changing conditions of their environment.”
Condamine was actually surprised by his own findings. He previously assumed dinosaurs were nowhere near extinction before the fatal asteroid smacked into our planet. Further investigation revealed that there were more terrestrial and semi-terrestrial dinosaur species roaming around 10 million years before the collision, many more than in the final years before they were all doomed to perish. Some paleontologists do believe that dinosaurs would have plodded on if the catastrophe had never happened. On the fossil record, their outlook appears bleak. That could change with evidence of new species appearing during certain periods.
Mystery still surrounds how and whether the dinosaurs went down so many millions of years before the asteroid. What looks like a lack of new species may in fact be the absence of fossils that would have been evidence for the evolution of older species that died out sooner. The only tyrannosaur species left to face the asteroid was T. rex.
It is possible that nothing replaced older species, but anything that might have has not surfaced yet. Despite those intimidating skeletons you see in museums, dinosaurs actually do not fossilize too well. It is possible that what remains unknown is either still buried or has vanished completely from the fossil record.
“Dinosaur diversification dropped in the 10 last million years before the impact,” Condamine says. “This diversification decrease is due to the increase of extinction that exceeds the speciation rate. This means that more species went extinct than species formed in this time frame. It seems that dinosaurs were not in good shape before the impact.”
There are some exceptions to the decline Condamine observed in the fossil record. Many marine species, including mosasaurs, are thought to have thrived in the open seas and continued diversifying right up until the great crash from space. Hadrosaurs, a duck-billed dinosaur species like Ducky in The Land Before Time, seemed to be both causes of other extinctions and survivors until the end. Condamine found that every time a new hadrosaur species appeared, other herbivores died out. This led him to conclude that they probably out-competed other herbivorous dinosaurs struggling to survive.
Dinosaurs are also believed to have been mesothermic — not exactly cold-blooded or warm-blooded — though a case for endothermy can be made for some rare species that were recently discovered in the Arctic and thought to have lived there throughout the year without migrating. A decrease in temperature of 12.6 degrees Fahrenheit may or may not have affected the adults. What it probably did affect was their offspring, since the sex of reptile embryos depends on the temperatures their eggs are kept at. A potential lack of males or females would have easily sent an entire species to its grave.
Could any dinosaurs have bounced back after the mass extinction? Theoretically, maybe. Hadrosaurs may have had what it takes, but these herbivores lost their main food source with the nuclear winter caused by all the smoke and ash that blocked sunlight necessary for plants to grow. Condamine also believes that there could be undiscovered evidence out there to prove him wrong.
“We have not studied the entire diversity of dinosaurs, so it is possible that some groups were not in decline,” he says. “Also, discoveries of new dinosaurs may influence the results, and the development of new models may allow for better estimates of diversity over time.”