The fossil record.
Not long at all and it happens frequently.
What do you see as the problem
I don't know what a "kind" is, do you?
Defining "Kinds" -- Do Creationists Apply a Double Standard?
So pigeons find an isolated island and take up residence there.
No predator, no need to fly.
Many years later there are no pigeons flying about but there are dodo
birds.
Since nobody knows what a "kind' is, and all agree that nothing
reproduces with offspring EXACTLY like parents...
Let me call dodo birds "pigeon kind".
But not variation within the original kind.
For lo, breed pigeons as you will, no two Paris pigeons
will hatch dodo eggs. Nor two wolves a peekapoo.
Creationists go off the rail pretty badly on "kind".
They accept wolf ancestry but know two bulldogs won't
give birth to a dalmatian.
They MIGHT even risk accepting that a dodo was "pigeon kind"
But pigeons as " dinosaur kind" is too tough apparently.
So little feathered dinosaurs are Chinese fakes.
The pneumatic bones are fake or misinterpreted.
The long dino type tail, teeth etc that are typical
dinosaur features found in early birds, well, none
are acknowledged.
But then it's hard to acknowledge something you don't know,
and no creationist here shows signs of even having taken
high school biology.
The shattering psychological shock of admitting they dont know
more than every scientist on earth and may not be consumate
masters of Bible interpretation is too much to risk anyway.