The problem, according to paleontologists Mark Goodwin and Jack Horner, is that many of the dinosaurs marked as unique species were actually pre-pubescent juveniles of other species! In one example cited, a variant of tyrannosaur that was previously considered to be a relative of Tyrannosaurus Rex was probably nothing but a young T-Rex before his "hormones kicked in".
It's funny: I'm old enough to remember when dinosaurs were regarded as slow-moving cold-blooded beasts that dragged their tails on the ground. Which as we know, isn't anything like how the latest research and pop culture currently depicts them as. And now maybe one-third of known dinosaurs never existed at all.
'Course, all of this is entirely within the realm of speculation since nobody has reported observing a real dinosaur before... right? :-)