Wednesday, December 22, 2010

Fossil of the Week

12/22/10 – Whale “Hands”

The 44-foot-long skeleton of a modern North Atlantic Right Whale (Eubalaena glacialis), known as Right Whale #2030,* hangs in the atrium above the Museum of the Earth’s Borg Warner Gallery, fully visible from the lobby and from outside the building through its surrounding glass windows. It is an iconic specimen, salvaged for the Museum by PRI staff when the whale washed ashore in late 1999 at Cape May, New Jersey.

The front flippers of the right whale are large, broad, and blunt. According to PRI’s director Warren Allmon in his book A Leviathan of our Own: the Tragic and Amazing Story of North Atlantic Right Whale #2030 (Paleontological Research Institution, © 2004), the flippers of this whale weighed more than 400 pounds (150 kilograms) each. As you can see in the photograph, the front flipper of the whale has five digits or fingers. Despite their vastly different size and function, the arrangement and the relative size and shape of the bones in the human hand and whale flipper are remarkably similar, and are evidence of a common evolutionary ancestor.

In the photograph, you can see the triangular shoulder blade (scapula) in the upper left, connected to the upper arm bone (humerus), connected in turn to the two parallel bones of the lower arm (radius and ulna). The five loosely floating bones that follow (mounted on a large piece of plastic in our whale) are the homologues** of our wrist bones (carpels). Notice that each finger has five bones instead of the four that you can count on your own hand. The distalmost four bones of each finger are equivalent to our finger bones (phalanges). But the fifth or basalmost bones of the fingers are homologous to the bones in the back of your hand (metacarpals) – this is identical to their position in our hands, but in humans is covered by the fleshy palm – the similarity is more clearly visible when one looks at the hand bones of a skeleton.

Although the bones of the whale’s flippers are real, calcified bones, they are apparently a little "spongier" and less stiff than those of most land animal. They merely serve as supports for the solid flipper, and do not have to support the animal.

*For more about Right Whale #2030, see Fossil of the Week 12/15/10 – Whale Pelvis and Hindlimb.

** Homologues are structure in two organisms that are alike or similar due to common ancestry.

Text by Paula Mikkelsen

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