article basics of mammals

 

February 20, 2007 Tuesday Late Edition – Final

SECTION: Section F; Column 1; Science Desk; BASICS; Pg. 1 LENGTH: 1093 words HEADLINE: A Mammal In Winter With a Furnace Of Her Own BYLINE: By Natalie Angier BODY: The other day a group of distraught construction workers in a Washington suburb contacted the local animal control agency with an unusual complaint. It seems there were seven large snakes wrapped around the heating pipes in a manhole, and the crew members worried that the snakes might be dangerous. I know exactly how they felt. No, not the construction workers, who were spooked by what turned out to be a collection of commonplace and quite harmless hognose and black rat snakes. I’m talking about those poor serpents. It’s been a vicious February, and I, too, have been tempted to weld myself to my home heating unit and to remain there, motionless, until the first summer markdowns. Alas, I cannot. For one thing, my daughter is blocking the vent, and when I try to push her aside, she hisses at me.

For another, I have no good phylogenetic or metabolic excuse. I am not a reptile. I am not at the mercy of the elements, ectothermically dependent on external sources of heat to spur my every move. I make my own heat, a prodigious, endogenous internal inferno, and with that enviable talent, that ability to maintain a steady core temperature however nature’s mercury may surge or plunge, I can plan my day more cannily and venture wherever I choose. Granted, the odds of my freely choosing to gambol in the snow are roughly equivalent to Dennis Kucinich’s shot at the presidency, but I could do it. I’d much rather celebrate the delights of being a warm-blooded homeotherm by visiting the splendid Hall of Mammals at the Smithsonian Institution’s Museum of Natural History, which offers the added attraction of being splendidly indoors. At the museum, visitors are reminded that mammaldom did not confer any major advantages on its earliest practitioners.

The first mammals were small, nocturnal, rodent-like creatures that skittered around the feet of dinosaurs for 140 million years. But when a giant asteroid barreled into Earth 65 million years ago, tossing up a fleecy quilt of dirt and ash that blocked the Sun, cooled the planet and killed off the dinosaurs along with about 70 percent of all living species, mammals and birds with their self-sufficient thermostats were able to weather the squalls, and the two groups quickly diversified to fill the ecovoids. Today, there are more than 5,400 members of the class Mammalia, ranging in scale from the tiny Kitti’s hog-nosed bat of Thailand, which at 1.5 grams is barely bigger than a carpenter bee, to the great blue whale, 90 feet long, 270,000 pounds heavy, and the most massive creature of any phylum ever to grace our world. ”You find mammals everywhere you look: on the ground, under the ground, near the highest mountaintops, in the sea and air, in arid deserts, super wet rainforests, on polar ice,” said Don E. Wilson, curator of mammals at the museum.

”And the key to their success, the reason they are the dominant life forms in such a wide range of habitats, is their ability to maintain a steady internal body temperature almost regardless of what’s going on outside.” With a predictably balmy internal milieu, the body’s enzymes can operate at a steady clip day and night, lending a mammal the freedom to snack, mate, bully the neighbors, sleep and snack some more as the mood strikes and opportunities arise.

A reptile, by comparison, must be perpetually attentive to prevailing winds, for if it eats too much right before a cold snap, its digestive enzymes could shut down prematurely and leave a partially undigested food bolus to putrefy and possibly kill the greedy gulper. ”The more stable your interior, the more independent a life you’ll lead,” said Richard Hill, an environmental physiologist at Michigan State University.

As always, however, there is no such thing as a free lunch, and we mammals must pay for the convenience of homeothermy by eating many extra lunches. The primary way we keep our personal thermostats set to a steady 37 degrees Celsius is through the relentless combustion of calories.

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