Let's study the heel in the caiman, the parrot, and T. rex.

First, click on the caiman's heel to take a close look at its shape.

Notice that the caiman has a distinct knob on its heel bone (calcaneum).

But what about the parrot?

Click on the parrot's heel to zoom in.

Notice that the parrot does not have this knob.

Caimans inherited a heel bone that is different from that of birds.

Now let's examine T. rex.

Click on its heel to see whether the knob is present.

Does T. rex have a knob on its heel bone?

a) Yes

b) No

c) We can't tell

This heel shape is a unique feature in caimans and other crocodiles.

Ooops. Look closer at the heel-bone of T. rex. Does it really have a bump? Try again!

Ooops. Look closer at the heel-bone of T. rex. Try again!