Some Dinosaurs Made Underground Dens

anthemaniac writes "Scientists have long puzzled over how some dinosaurs and other creatures survived the asteroid impact that supposedly caused the KT mass extinction 65 million years ago and wiped out all the big dinosaurs. One idea has been that smaller animals, including mammals, could have endured the fallout, the big chill, the subsequent volcanoes, and whatever else by burrowing. Now scientists have come up with the first evidence of burrowing dinosaurs. They speculate that underground dens might explain how some dinosaurs got through long, dark winters at high latitudes, too."

Re:On the evolutionary tree...

[linguizic]

Burrowing, like all behaviors, can't really be traced phylogenically for a couple of reasons:1.As this article shows us, it's hard to find evidence of behaviors that happened yesterday let alone millions of years ago (though under the right conditions burrowing does leave a trace, as the article shows), 2. Behaviors vary more wildly than the average allele. Though there is a large component of genetics at play with behavior, ultimately behaviors are products of the physiological phenotypes associated with said alleles and sensory input. Different environmental inputs yield different behavioral outputs for the same allele. Therefore there isn't an isomorphic relationship between genes and behavior. Behavioral traits tend to pop up independently of each other quite often, so it is impossible to say that there is one node on the evolutionary branch that "sprouted modern burrowing/hibernating reptiles and mammals".

Granted this is coming from what I learned as an undergraduate so there are probably better people in the /. community to comment on this. (That's my way of saying: "Though I may sound like an expert, I very well may be full of crap and would love it if someone with more knowledge would fact check this post").

Re:Dinosaur extinction breaks my brain

[robson]

Dinosaurs is what we call the reptiles that went extinct about 65 million years ago.

That should answer your question why all the dinosaurs went extinct. They're defined that way.

Okay, riddle me this: Why did no reptile whose legs extended below the body ("dinosaur") rather than to the side ("lizard") survive, regardless of their scale, location, or diet?

That aside, while researching a reply, I found something close to what I was looking for on Wikipedia [wikipedia.org] (though the section is marked as needing citations):

Possible patterns and trends

Despite its overall severity, the K-T extinction was rather patchy. This raises the question of why some groups died out while others did not.

There do seem to be some general trends:

* Organisms which depended on photosynthesis became extinct or suffered heavy losses - from photosynthesing plankton (e.g. coccolithophorids) to land plants. And so did organisms whose food chain depended on photosynthesising organisms, e.g. tyrannosaurs (which ate vegetarian dinosaurs, which ate plants).
* Organisms which built calcium carbonate shells became extinct or suffered heavy losses (coccolithophorids; many groups of molluscs, including ammonites, rudists, freshwater snails and mussels). And so did organisms whose food chain depended on these calcium carbonate shell builders. For example it is thought that ammonites were the principal food of mosasaurs.
* Omnivores, insectivores and carrion-eaters appear to have survived quite well. It is worth noting that at the end of the Cretaceous there seem to have been no purely vegetarian or carnivorous mammals. Many mammals, and the birds which survived the extinction, fed on insects, larvae, worms, snails etc., which in turn fed on dead plant matter. So they survived the collapse of plant-based food chains because they lived in "detritus-based" food chains.
* In stream communities few groups of animals became extinct. Stream communities tend to be less reliant on food from living plants and are more dependent on detritus that washes in from land. The stream communities may also have been buffered from extinction by their reliance on detritus-based food chains. (See Sheehan and Fastovsky, Geology, v. 20, p. 556-560.)
* Similar, but more complex patterns have been found in the oceans. For example, animals living in the water column are almost entirely dependent on primary production from living phytoplankton. Many animals living on or in the ocean floor feed on detritus, or at least can switch to detritus feeding. Extinction was more severe among those animals living in the water column than among animals living on or in the sea floor.
* No land animal larger than a cat survived.
* The largest air-breathing survivors, crocodilians and champsosaurs, were semi-aquatic. Modern crocodilians can live as scavengers and can survive for as long as a year without a meal. And modern crocodilians' young are small, grow slowly and feed largely on invertebrates for their first few years - so they rely on a detritus-based food chain.

More evidence...

[Brad1138]

Now scientists have come up with the first evidence of burrowing dinosaurs. They speculate that underground dens might explain how some dinosaurs got through long, dark winters at high latitudes, too.

I believe this [photobucket.com] proves it beyond a doubt.