Most of what we know to be civilization has only occurred in the last 10,000 years and most of that only in the last 4000 years. And most of the really wild stuff only in the last 500 years.
Say 60 million years from now an alien species comes to earth and in an effort to discern where humans came from —they start digging in the dirt.
What they will find is a layer without humans and right on top of that —a layer with humans.
No transition.
Nothing.
First our bones and our stuff are not there and then our bones and our stuff are there in the dirt.
That’s it.
No transitional forms.
it’ll look like maybe humans came from outer space because as quickly as our stuff appears in the dirt the spent cases of rocket ships will be there.
My point?
likely the vast changes in animal architecture happened very very rapidly in terms of geological time. Something set up a genetic cascading effect.
SURELY that would be a LOT easier to find.