I'm Donald Henderson. I'm one of the curators 
here at the Royal Tyrrell Museum.
I want to show you an example of evolution 
in action and how animals transform.
This is an ichthyosaur. It's a marine reptile.
Its ancestors lived on land in the Triassic.
But they evolved this perfect body form
for living in the water. You can see, here's the original
upper arm bone. They turned their arms 
into little flippers for steering.
They also evolved a dorsal fin 
for stability. One of the differences
between reptiles and mammals: 
our ribs stop about halfway.
But in reptiles, the ribs continue all
the way back to the hip region,
because they have a different 
way of breathing.
