The strange bones of birds

13 01 2012

Structure circled in yellow: dragon skull, or bird sternum?

Seanetter Libby Rock can always be counted upon to identify potential supernatural or phantasmagorical finds on the beaches and on this blog. Noting the bony structure attached to the wigeon wings on the last post, she suggested dragon skull for the i.d. In fact, the structure is a severely displaced sternum. While the sternum in mammals like ourselves is a thin, flat bone, in birds, it is a wide, shield shaped bone with a deep keel projecting out to give a sturdy attachment zone for the massive pectoral muscles birds require for flight.

A bird's sternum in profile (left) and head on (right). Bonus points: can you spot the fracture?

Fused pelvis and vertebrae in birds: an adaptation for the rigors of flight.

Another evolutionary adaptation for flight is demonstrated by a bone photographed by Jack Renfrew, who sent in a pic of a mystery specimen much like the one in the second photo. The structure shown in this photo is actually the fused lower vertebrae and pelvis of a Northern Fulmar. Flight is a very energy intensive and demanding activity, and the sheer force of the powerful downbeat of the wings would cause a very flexible skeleton (like ours) to bend ineffectively making the bird incapable of taking off. The fusing of multiple bones together through evolutionary time is a theme throughout the avian skeleton; where humans have 206 bones, birds typically have fewer overall, though the loss of flexibility in the mid and lower spine is compensated for by additional vertebrae in the neck. These “extra” bones (compared with mammals) are responsible for the ability of birds to turn their heads as much as 270º, though the common belief that birds can spin their heads all the way around is nothing but a goofy, Exorcist-style myth.

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3 responses

4 08 2013
Abigail

Do you know what species that bird sternum is from? I have one very similar to it that I am trying to identify.

6 08 2013
scourc01

Hi Abigail! Yes, that one on the black background is a murre sternum. It’s elongated and kind of skinny side to side. Some great sites for you to use to try and figure the bone you found are Aves3D and seabird osteology. Of course, we’re always happy to take a look at it too!

6 08 2013
Abigail

Thank you! I did run across those websites and was able to identify it. I appreciate your help!

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