Why do elephants have trunks?
|By Kathy Wollard|
Illustration by Debra Solomon
|Why do elephants have trunks? asks J. Navarrete, a student in
Imagine life with a trunk: Sniff a friend's sandwich, then grab it with your nose. Reach for something on a high shelf without standing on a chair. Swim across a pool underwater, using your long nose as a snorkel.
There are no bones in an elephant's trunk, making it as supple as a garden hose. A trunk has more than 40,000 muscles and tendons, and its tip is covered with nerve endings. In addition, there are one or two "fingers" on the tip to grasp small objects. Like a monkey's tail, a trunk is "prehensile," and can be wrapped like a rope around an object such as a branch. Unlike a monkey's trail, an elephant's trunk can weigh 400 lb. and measure 7 feet long.
All of this makes a trunk flexible (it can hoist a log), strong (the log can weigh more than 300 lb.) and precise (it can pick up a penny lying flat on the floor).
An elephant's trunk is the Swiss army knife of animal appendages. A trunk-equipped elephant can: Collect gallons of water, and then give itself a quick shower. Snatch the highest, tastiest leaves off a tree. Use its trunk like a periscope to sniff the air for danger. Sprinkle dust on itself to protect from biting flies. Pick up a peanut. Give another elephant's trunk an affectionate squeeze. Change its nostril size to change the sound of its voice.
An elephant can also wade into a lake, submerge, and use the tip of its trunk as a snorkel as it swims to the other side, breathing easily all the way. Human beings, on the other hand, can only use snorkel tubes that are about a foot long. Snorkel deeper, and the mismatch between air pressure inside lungs and the increasing pressure just outside can make blood vessels swell and rupture.
Elephant lungs are different, according to John West, a University of California scientist who studies lungs. Instead of having a pleural space between lungs and chest wall as we do, elephants have dense sheets of fibery tissue. This tissue allows elephant lungs to withstand pressures that would cause human lungs to collapse. A sign, according to scientists, that elephant ancestors were aquatic creatures.
More evidence: Elephant fetuses start out with funnel-shaped kidney ducts, like freshwater fish and frogs. While the aquatic-style ducts disappear as the unborn elephant grows, their presence early on is a marker of a watery past.
The elephant's trunk, many scientists think, may have first evolved as a snorkel. But trunks were also useful for gathering sea grasses to eat. The closet living relatives of the elephant may be sea cows, like manatees.
The land-dwelling ancestors of today's elephants emerged from their aquatic origins about 30 million years ago. Animals born with long trunks had an advantage, since trunks were so useful for gathering food out of reach of many other animals. Eventually, modern elephants with long, strong trunks evolved and flourished.
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Copyright © 1999-2003 by Kathy Wollard & Debra Solomon