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Re: Why did small dinos become extinct?



John Scanlon suggests that lizards and snakes helped to squeeze dinos out of the small terrestrial predator niches. Andreas Johansson suggests birds were implicated. Tim Williams points out the the birds took heavy losses. Various others have asked why I keep raising the question when all the pieces seem to be in place.

Can anyone supply references to peer-reviewed articles that discusss the possibility that small non-flying predatory dinos were squeezed out by lizards & snakes and / or birds and / or mammals and / or juveniles of larger dino predators? Among other things I'd like to nail this down in a Wikipedia article.

On the other hands there's meagre but apparently growing evidence of small Maastrichtian non-flying theropods. Tim Williams says Richardoestesia was a small Maastrichtian non-flying theropod. My googling have come up with only the info that it was described by Currie, Rigby and Sloan in 1990. "Small theropod and bird teeth from the late Cretaceous (late Campanian) Judith River Group, Alberta" (Sankey, <http://findarticles.com/p/search?tb=art&qt=Sankey%2C+Julia+T>Brinkman, <http://findarticles.com/p/search?tb=art&qt=Brinkman%2C+Donald+B>Guenther, Merrilee <http://findarticles.com/p/search?tb=art&qt=Guenther%2C+Merrilee> and Currie; <http://findarticles.com/p/search?tb=art&qt=Currie%2C+Philip+J>Journal of Paleontology <http://findarticles.com/p/articles/mi_qa3790>, Jul 2002 <http://findarticles.com/p/articles/mi_qa3790/is_200207>; http://findarticles.com/p/articles/mi_qa3790/is_200207/ai_n9134486/pg_12) refers to a 1990 paper by Currie, Rigby and Sloan called "Theropod teeth from the Judith River Formation of southern Alberta, Canada", in "Dinosaur Systematics: Perspectives and Approaches" edited by Carpenter and Currie, Cambridge University Press). The Judith River Group is AFAIK earlier than the Hell Creek Formation, which spans the K-T boundary. Bigelow's list of Hell Creek fossils (http://www.dinosauria.com/jdp/misc/hellcreek.html, last updated Nov 2004) lists Richardoestesia / Ricardoestesia as a jaw / tooth taxon, and all the other small theropod fossils are jaws / teeth. http://www.dinodata.org/index.php?option=com_content&task=view&id=689&Itemid=25 reports diverse small theropods and no large ones from the Hateg Basin (latest Maastrichtian, Roumania). Sampson, Carrano & Forster reported an unusual 1.8m theropod from Maastrichtian Magagascar ("A bizarre predatory dinosaur from the Late Cretaceous of Madagascar", /Nature/ *409*, 504-506, 25 January 2001, http://www.nature.com/nature/journal/v409/n6819/full/409504a0.html).

The bottom line at present appears to be that there's evidence of small Maastrichtian non-flying theropods but it's hard to pin down when they became extinct because at present the Hell Creek formation is the only terrestrial fossil bed that includes the K-T boundary.

Does this mean I have to conclude that at present we don't have enough info to say much about how and when small non-flying predatory dinos became extinct? If anyone has said this in a peer-reviewed publication, could someone please provide a reference.

John Scanlon wrote:
Philip Chalmers wrote:

Despite the thoroughness of David Marjanovic's response I think there are still some gaps:

"Because they (small non-flying dinos), or most of them at least, did not have similar ecological niches. The surviving mammals and lizards mentioned above were for the most part granivores and insectivores; of the only dinosaurs in these niches, some survived -- all of them happened to be neornithean birds (and lithornithids, if those don't belong to Neornithes)."
Why were small dinos excluded from these niches?
Why could small dinos not survive by preying on the granivores and insectivores, as cats do now?


"No flightless theropod the size of *Compsognathus* or smaller is currently known from the Maastrichtian, AFAIK." That's also my impression, but the question is why not, given that there were earlier very small flightless theropods?

These two points are the central part of the question I originally raised. The only explanation I can think of is that small flightless theropods were squeezed out by the young of larger theropods and by small predatory mammals (successors of Repenomamus). The young of larger theropods were doomed because they grew to a size where they needed to prey on large herbivores, which were exterminated by the catastrophe(s). Are there better theories?

[snip

... I was asking what feature(s) of dinos or of latest Cretaceous ecosystems made it impossible for small non-flying theropods to survive.

Might I humbly point to the success of squamates in the small terrestrial
predator niches? Varanoids and snakes commonly reach larger body sizes than
Compsognathus et al., are well equipped for gobbling granivores and
insectivores but need much less energy than similar-sized mammals (or
probably dinosaurs), and they were more or less global in distribution by
the end of the Cretaceous after only starting to show up in the mid-Early K.
They show good lineage survival through the K/P boundary, which probably has
something to do with being able to fast for a year or more (especially in
relatively low temperatures). This is all pretty well known stuff, and does
it not seem sufficient to answer your question?



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