The shape of the shoulder socket affects the movement of the arms.

A pigeon's shoulder allows the arms to flap during flight.

This motion is possible due to the orientation of the shoulder socket, shown here by a red arrow.

We will refer to this type of shoulder as an "up" shoulder because it allows upward motion.

Some species had shoulder sockets that allowed outward movement of the arms.

We will call this type of shoulder socket the "out" shoulder.

In other species the arms were restricted to forward and backward movement by a "down"-oriented shoulder socket.

Here we see each type of shoulder socket mapped onto the cladogram.

Click on the lineage where you think the "out" shoulder socket first evolved.

Velociraptor was the first to have a shoulder directed outward!

Oops!

Try again.