The end of the dinosaurs was clearly linked to an asteroid impact that brought the Cretaceous period to a close. But the details of their end have remained a matter of debate since the impact crater was discovered. There is a lot of evidence that the impact alone should have been enough to do them in. But the asteroid arrived amid major volcanic eruptions associated with previous mass extinctions. And fossils dating to just before the impact have suggested that dinosaur-dominated ecosystems had become less diverse, making them more prone to collapse.
Now, a new study has revealed that fossils we already know about originated within the last few hundred thousand years before the impact that killed off all dinosaurs except birds. The results indicate that species richness wasn’t likely to be a problem—at least in the neighborhood of the impact itself.
Wyoming vs. New Mexico
Most of what we know about the last days of the non-avian dinosaurs comes from the Hell Creek Formation, rich fossil beds in present-day Wyoming. These not only date from within a few hundred thousand years prior to the impact, but there may be deposits that capture the immediate aftermath of the impact. Beyond this area, which reflects the ecosystem of the northern Great Plains, we have little else. It hasn’t been clear whether the diversity of species present at Hell Creek reflects what was present more globally, or if there were regional differences in ecosystems
