From Legs to Flippers: Whale Bones at the Stranding Center

Laying Out a Whale

1Last spring a 7-meter minke whale stranded on the beach near the Gull Point Marine Mammal Center and could not be saved. Center staff buried the body in sand for a year so that tiny organisms would clean the bones. This fall, volunteers began laying out the skeleton for a teaching display. Eighth grader Tamsin Okafor, who volunteers on weekends, sorted the bones with the center's biologist, Dr. Renata Vukovic.

2Inside each flipper Tamsin found one upper arm bone, two lower arm bones, a cluster of wrist bones and long rows of finger bones. In life, skin and tissue wrapped them into one stiff paddle. The skull had two nostril openings on top of the head, where the blowhole had been. Near the middle of the body lay two small, rod-shaped hip bones. They had been loose in the muscle, not attached to the backbone, and the whale had no leg bones at all. Dr. Vukovic also showed Tamsin the ear bones. Each one sits in a shell of bone with an unusually thick, heavy wall, a feature found in living whales and dolphins.

3Like other mammals, minke whales breathe air, and mothers feed their calves milk. A shark also swims with fins, but it is a fish. Its fins are held stiff by thin rods of cartilage, with no finger bones, and its tail fin beats from side to side. A whale's tail beats up and down.

4A university lent the center casts of three fossils found in rocks in Pakistan and Egypt. Pakicetus, about 50 million years old, was a wolf-sized animal that walked on four legs near rivers. Rodhocetus, about 47 million years old, had short legs and large feet and probably swam by kicking. Dorudon, about 38 million years old, was about 5 m long and lived its whole life in the sea. Its hind legs were far too small to hold up its body. All three fossils, like hippos and deer, have one upper arm bone and two lower arm bones in each front limb.

5The university also lent foot skeletons of a hippopotamus and a deer. In hippos, deer, cows and pigs, one ankle bone is grooved and rounded at both ends. It is called a double-pulley ankle bone, and among living mammals only this group of hoofed animals has it. Dr. Vukovic reminded Tamsin that animals can look alike because they do the same job, so she should compare detailed bones, not just body shapes. Tamsin recorded the features in a table.