Yes, it's a penguin flipper! Here's the whole scene:
The head would have been at the bottom of the photo and the feet at the top. The big bone sticking out is the keel where all the breast muscles attach. Strong fliers or swimmers have strong keels with strong muscles attached.....it all makes sense.
Closeup of the side of the keel.
"Where d'ya think Bob went?" "I dunno....wanna go cruise babes?"