Given the immense amount of time that life has been around, all sorts of low probability events have occurred. One rare class of happenings is called sweepstakes dispersal. Oceans separating islands or continents form barriers to most terrestrial animals. The chances of getting across is so small that many thousands of attempts are lost, ending in death. But on very rare occasion, one may make it through—a winner! And thus, of course, the term "sweepstakes".
North and South America were separated from one another by water from
the time of the dinosaurs until the Central American land bridge formed just a few
million years ago. Each continent evolved its own animals, independent of the
other—except somehow a South American ground sloth became a winner. This was the
ancestor of one of the Chihuahuan Desert's Ice Age giant ground sloths,
Megalonyx. As with other ground sloths, late comers all, it died out at the end
of the Ice Age. Nevertheless, several million years of happy residence in North America
accrued to this animal that beat the odds.
Contributor: Arthur H. Harris, Laboratory for Environmental Biology, Centennial Museum, University of Texas at El Paso.
Desert Diary is a joint production of the Centennial Museum and KTEP National Public Radio at the University of Texas at El Paso.