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Why did small dinos become extinct?



The standard type of explanation for the extinction of the dinosaurs is "Vegetation was devastated by catastrophe(s) which shut down photosynthesis, so vegetarian dinos starved to death, and carnivorous dinos quickly followed them." To explain why birds and mammals survived the end-Cretaceous extinction, the same type of theory says something like, "They ate seeds and invertebrates, i.e. their food chains depended on seeds and detritus rather than vegetation. In addition many of them were burrowers and / or divers, so had some protection again the effects of the catastrophe(s)."

I have always been puzzled about why no burrowing or small predatory dinos survived the K-T extinction. Small small predatory dinos should have been able to feed on birds, mammals, lizards and small amphibians, which survived rather well - in other words, small predatory dinos should have survived at the top of the detritus-based food chain.

We now know of burrowing dinos (Oryctodromeus and possibly Orodromeus). Admittedly Oryctodromeus was vegetarian and Orodromeus was a close relative, so both were doomed under the standard explanation. But why were there no burrowing small predatory dinos in the latest Cretaceous or, if there were, why did they perish?

The only answer I can come up with is that there were no small predatory dinos in the latest Cretaceous, burrowing or otherwise. http://www.dinosauria.com/jdp/misc/hellcreek.html says Dromaeosauridae represent only about 2% of the paleopopulation at Hell Creek and Troodontidae only 1% - and both groups are represented only by teeth. The fact that these groups are represented only by teeth is a little suspicious and may point to re-working. And Troodon's teeth have led some researchers to suggest that it was an omnivore or even vegeratian (Holtz, T.R., Jr., Brinkman, D.L. and Chandler, C.L. (1998). "Denticle morphometrics and a possibly omnivorous feeding habit for the theropod dinosaur /Troodon/." /Gaia/, *15*: 159-166)

The best explanation I can think of for the absence of latest Cretaceous small predatory dinos is that they died out earlier as a result of competition from birds, mammals (ecological successors of Repenomamus) and juveniles of larger carnivorous species - and juveniles of larger carnivorous theropods were doomed because they grew and in a few years had to depend on the photosynthesis-based food chain. But I've been unable to find anything that might support this idea.

Can anyone provide or point to a good explanation for the extinction of the small predatory dinos? If so, could you please provide names and authors of relevant books / articles.




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