Tuesday, April 19, 2016
[Geology2] Re: Dinosaurs 'already in decline' before asteroid apocalypse
The article is a little misleading when it says that paleontologists "previously thought that dinosaurs were flourishing right up until they were wiped out by a massive meteorite impact 66 million years ago." In 1965 paleontologist Edwin Colbert discussed the decline of dinosaurs in his book "The Age of Reptiles", backing it up with a table and graph showing the declining number of genera in the late Cretaceous of North America. As far as I know, that idea has been pretty well accepted over the years.
I'm not sure that the Bristol study, as it's described here, adds much to our understanding but it does provide more solid evidence on the subject and could lead to more targeted investigations of the world the dinosaurs lived in at that time.. The article gives the impression that dinosaurs were in big trouble as the Cretaceous wound down, and were headed for extinction whether an asteroid hit or not. but there is no evidence of that in the fossils they left. The great number of bones found right up to the extinction event suggest that the dinosaurs were present in abundance right to the end, and those bones don't show the signs of physical distress we would expect from a hostile environment. So the interesting questions are 1) why was generic diversity declining and 2) what would be the end point of that process: extinction, or simply an ultimate static lower level?
Something in the late Cretaceous environment was changing and the dinosaurs were responding to it. If the people at Bristol can do detailed studies of the generic diversity among other animals that lived during this time it might tell us if the problem was restricted to the dinosaurs or something in common with other groups. Species diversity is related to habitat diversity, and both of those are vulnerable to climate change and changes in atmospheric chemistry.
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