Post your wild theories about why dinosaurs were so big:
January 29, 2014 8:19 PM Subscribe
To ask the question another way, why are modern land vertebrates so small? If it's to do with environmental factors, which ones?
posted by 8k to Science & Nature (18 answers total) 6 users marked this as a favorite
Convergent evolution suggests that a body shape that "worked" from c.200mya to c.65mya should still "work" now. But that's not the case: the biggest modern land mammal ever, paraceratherium, was about the same size in mass terms than triceratops, which wasn't one of the bigger dinosaurs. The biggest bird, aepyornis, was half a tonne. So something has changed -- what?
I've seen arguments about the type of vegetation, atmospheric oxygen, but nothing that really explains it. Are mammals and birds in some way genetically incapable of attaining those sizes -- and if so, why were birds' close relatives, the huge therapsids and sauropods, capable of it?
I'd really like to hear good or speculative ideas on this. What about parasites? Plate tectonics and gigantism? Warmbloodedness seems to have fallen from favour and there's the whole debate about whether dinosaurs were warmblooded, but could that explain it?