What really killed the dinosaurs?

15 May 2018

Question

What really killed the dinosaurs?

Answer

Chris Smith put this to palaeontologist Jason Head...

Jason - There are two answers to that question. The first, of course, is that dinosaurs are doing fine today; there’s about 18,000 species of living birds. But the second half of that question is what happened to dinosaurs that aren’t birds? And the last of the non-bird dinosaurs go extinct around the end of cretaceous, that’s 66½ million years ago. That coincides with very strong geological evidence for an extraterrestrial impact of an asteroid or another form of bolide. It appears to be a fundamental global environmental change that corresponds with a mass extinction event in both terrestrial and marine environments. So for the non-birds, it appears that the very last of them went extinct possibly as a result of  this impact.

Chris - Were there not some enormous volcanoes going off at around the same time that were also had the potential to make similar changes to the Earth’s climate and the Earth’s atmosphere?

Jason - Yeah. So the last million or two years of the cretaceous of the mesozoic, there’s what is called flood salts in India, the Deccan Traps which are a kilometre and a half thick sequence of volcanic rock formed from these massive volcanoes, and they absolutely are changing Earth’s atmospheric chemistry during this period of time. They are a big and important component of a changing environment.

Chris - Kate?

Kate - If the crater theory is what happened, and this big catastrophic event is what knocked out all of the giant dinosaurs, do you think that it was required for that sort of geological historical event to happen in order for mammals to become so successful, and ergo humans to have become what we are today?

Jason - We think a lot about that. Whether or not the rise of mammals in the cenozoic is the result of ecological release or the loss of competitive exclusion, and there’s some pretty good evidence that that might be the case. Certainly patterns of body size evolution in mammals show that they get bigger when the dinosaurs are gone. We diversity as a clade within a couple of million years of dinosaurs having gone extinct so I think it’s tricky to pin that down 100 percent, but the evidence looks pretty good for it.

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