Undeniable Fact: They grow up so fast

Paleontologists have recently discovered that the tyrannosaurus and brontosaurus were actually the same animal. The tyrannosaurus is merely the larval stage of the larger brontosaurus. This explains their small arms which were previously believed to be vestigial.

This does of course put the nail in the coffin of the idea that dinosaurs were related to birds or reptiles. They were amphibians.