Why Were Dinosaurs So Big?

Why were dinosaurs so big?: originally appeared on Quora: The best answer to any question. Ask a question, get a great answer. Learn from experts and access insider knowledge. You can follow Quora on Twitter, Facebook, and Google+. Answer by Marc Srour, Invertebrate Paleontologist Image by MathKnight There is actually no uncontroversial explanation for the as-of-yet unparalleled size of dinosaurs. If you look at the distribution of large sizes in dinosaurs, one distinction becomes clear: the only dinos that were small (less than 1m) were carnivorous theropods. Except for the 70 cm Fruitadens Haagarorum, no herbivorous ornithischians were small. The evolution of teeth in ornithischian lineages proceeded along very similar lines independently, and each innovation was accompanied by a bump in body size. Teeth are merely the most fossilisable sections of the digestive system. If they changed, then the rest of the animals' physiology was also changing in such a way as to enable larger body sizes, from getting larger guts to becoming quadrupedal (the first ornithischians were small and bipedal). In turn, this leads to changing ecological opportunities, feeding on different plants, being able to eat much more at once, and thus beginning the cycle of ever-growing sizes. This would then enter into a coevolutionary back-and-forth with their theropodan predators, eventually resulting in the sauropods, tyrannosaurids, and the other giants. What were the ornithischians eating to...
Source: Science - The Huffington Post - Category: Science Source Type: news