Wednesday, December 29, 2010

Fossil of the Week

12/29/10 – Whale Blowhole

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 whale’s blowhole is not immediately obvious from many angles of observation in our Museum. From outside the glass windows, however, this view makes it quite clear. It is through this orifice that a whale exhales in a geyser of air, saltwater, mucus, and metabolic wastes – prompting “Thar she blows!” from many a whaler in the past. The blowhole, high on the whale’s forehead, is the equivalent (the homologue** in scientific terms) to our nostrils. Although it looks like a single hole in the photograph, there are actually two holes here, which are angled slightly away from each other, producing the distinctively V-shaped opening characteristic of in right whales. [Toothed whales, such as the sperm whale, have only one opening – both openings are present, but only one opens to the surface.] The advantage to the air-breathing whale in having its nose in such a location is to be able to breathe while mostly submerged in water.

The earliest known fossil “whales” are called archaeocetes, and they were probably at least partly terrestrial (they had hind limbs!). Archaeocetes had nostrils near the tip of the snout, like land mammals do, rather than a blowhole on the top of the head. Genetic evidence suggests that the closest living relatives to whales are members of the family Hippopotamidae, which includes the modern hippopotamus.

The blowhole is also involved in whale sounds and communication. Air sacs just below the blowhole are filled with air, which is released to produce sound as happens when air is released from a balloon. The whale’s trachea or windpipe connects to the blowhole just as ours connects to our nose, but unlike us, there is no connection to the esophagus. So the whale has no risk of food accidentally ending up in the animal's lungs; likewise a whale cannot breathe through its mouth like we and most other mammals can.

*For more about Right Whale #2030, see Fossil of the Week 12/15/10 – Whale Pelvis and Hindlimb, and 12/22/10 – Whale “Hands.

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

Text by Paula Mikkelsen

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