Jeffrey Moussaeiff Masson - Altruistic Armadillos, Zenlike Zebras: Understanding the Worlds Most Intriguing Animals

A RMADILLO IS A SPANISH WORD REFERRING TO THE ARMORLIKE shell protecting this remarkable animal. This defense system led early zoologists to classify them with turtlesand allowed this animal to survive for 55 million years. I recently saw a photo of an armadillo on the Web that totally captured me: It was rising vertically in the air. The caption explained that when armadillos are surprised, they often jump straight up! Travelers in Americas Gulf States often see them by day scattered along the roadside after theyve been killed during the night by cars and trucks. But being hit by the wheel isnt what kills them. Rather, it is their unusual jump reflex: When a car roars over them, they bound off the road almost vertically, hitting a cars underside. I am not sure how this startle response evolved. Did it unnerve their predators? And then of course there are species of armadillos constructed so that they can curl up in a ball, completely safe from any predation.

Armadillos are distant cousins of anteaters and sloths, who originally come from South America. There are at least twenty species, ranging from the fairy armadillo, only 5 inches long and weighing in at 3 ounces, to the giant armadillo, who is almost 4 feet long and weighs 130 pounds. The best known is the nine-banded armadillo Dasypus novemcinctus (so called because of the nine movable bands on the like skin). Perhaps the term best known glosses over the fact that almost nothing is known about the other living armadillos, even less about the extinct ones. The nine-banded armadillo existed in the United States several million years ago and then vanished five to ten thousand years ago for unknown reasons, only to reemerge in Texas in 1854. (Today they are found from Argentina to Colorado.)

We tend to associate the nine-banded armadillo with the Lone Star State, primarily because Texans have taken to armadillos. Just this one species of armadillo lives in Texas. And a good reason they are welcome is that, like their cousins, they are inordinately fond of ants, especially fire ants, the scourge of the state. For some reason, armadillo races are popular with humans in Texas, though there is no evidence that armadillos share the enthusiasm.

Scientists are fond of armadillos for a number of reasons. One is that a reproducing female armadillo can delay implantation for several months, and gestation can last up to twenty monthsas long as an elephant. The New Encyclopedia of Mammals (2001), reports a case where a female gave birth three years after the last date at which she could possibly have been inseminated! Thats not all: After this long gestation, she gives birth to identical quadruplets, all coming from a single egg. The embryo divides in two, and those two embryos divide into two more. Armadillos are the only mammals who routinely give birth to genetically identical quadruplets. Derived from a single fertilized ovum, all the babies are of the same sex and all contain identical sets of genes, a treasure trove for geneticists.