Psst... over this way

Psst... over this way, originally uploaded by SwirlingStillness.

Curiously, at least one ice-age giant may return to North America even without the help of humans. Fourteen thousand years ago much of North America south of the latitude of New York was inhabited by a giant armadillo known as Dasypus bellus. At about twenty kilograms it was three times as heavy as the living armadillo, but otherwise the two were virtually identical. Beginning about 13,000 years ago the giant armadillo was driven out of what is now the United States. Human hunting was likely responsible, for the large armadillos probably hibernated in fissures among rocks, where they were easily spotted and dispatched. Some armadillos, however, survived in the dense rainforests and rugged terrain of Central America. These were smaller than those living further north, and they like many species, have shrunk in average body size over the past 13,000 years. This is because they were hunted assiduously by the Indians who considered them a delicious repast and, as we have seen, hunting pressure can lead to the selection of rapidly maturing dwarfs.

As the Indian population itself began to decline in the seventeenth century and hunting pressure eased, the selective pressure felt by the armadillos reversed. Small armadillos began a rapid advance north. Between 1905 and 1914, at the height of their northward charge, they advanced at a rate of more than twenty-five kilometres a year. Today's small armadillos have still not reached as far north as their giant ancestors did 13,000 years ago. This is because they are more likely to die during cold winters than large armadillos-they cannot accumulate as much fat and they lose heat more rapidly. As cold winters kill the smaller individuals, however, natural selection is acting upon the advance guard in the armadillo invasion and they are again increasing in size. If the trend continues, in a few centuries from now the giant Dasypus bellus may once again stalk the Appalachian forests and thrive as far north as New York.

From The Eternal Frontier. by Tim Flannery (William Heinemann: London, 2001) pp. 347-348

(special thanks to Stuart on flickr for this great photo, and the post title, you can see other great photos by him here)