Quoting McWhorter ( http://www.booksandculture.com/articles/2010/janfeb/reanimation.html?paging=off ): “Sampson thinks mesothermy explains a lot of other things about dinosaurs that otherwise seem just so. For example, one branch of theropods that yielded fecund subbranches (i.e., countless additions to The List) were apparently actually warm-blooded. This has become clear from gorgeously detailed fossils unearthed in China of late, revealing feathers, not for flying but for warmth. However, this does not mean that feathers were a quirk of dinosaurs in China: relatives of the same theropods have long been known from elsewhere but not as exquisitely preserved, meaning that the living creatures had feathers, too.

Sampson notes that these warm-blooded theropods are exactly the ones that did not trend toward the enormous. For example, the Velociraptor/Deinonychus type was among them, and there was no version the size of a building. Presumably it was because warm blood puts a limit on how big you can get. This is also the only branch of theropods that includes some varieties that went vegetarian (Naish’s book, in a rare lapse, does not include a picture of these massive, pot-bellied freaks with Edward Scissorhands claws). Sampson traces this vegetarianism to warm-bloodedness as well: it’s a challenge for carnivores to find enough food to keep their high metabolism going, and easier to do the trick eating plants, which have the courtesy to sit still while being eaten.”