The giant ground sloth from London’s Natural History Museum was once a dominant species in North America. (Credit: Ballista)
Today, if you searched all of North America north of Mexico, you would find only 17 species of land mammals that could be called megafauna, a term for animals that exceed 100 pounds. If you exclude the rare predators and arctic animals, you are left with just 10 species: pronghorn, mountain goat, bighorn sheep, bison, elk, moose, mule deer, white-tailed deer, black bear, and grizzly bear.
If not for the end-Pleistocene extinctions just 13,000 years ago, there would still be another 40 species of North American megafauna. They would include five species of deer or moose, two llamas, a camel, three horses, four ground-sloths ranging from 400 pounds to 3 tons, a 600-pound armadillo, a 2,000-pound turtle-like glyptodont, two ox-like species, a 5-ton mastodon, a 6-ton woolly mammoth, and a 9-ton Columbian mammoth. Did I mention the 400-pound beaver? Before you jump into your time machine for a true North American safari, be advised that there were also scimitar-cats, American lions, and sabertooths, each as big as or bigger than an African lion. There were three huge bears, including the 1,800-pound giant short-faced bear, the largest mammalian predator that ever walked the Earth.
Now let’s return to the forlorn fruit of the Osage orange. Nothing today eats it. Once it drops from the tree, all of them on a given tree practically in unison, the only way it moves is to roll downhill or float in flood waters. Why would you evolve such an over-engineered, energetically expensive fruit if gravity and water are your only dispersers, and you like to grow on higher ground? You wouldn’t. Unless you expected it to be eaten by mammoths or ground-sloths.
According to my field guide, Osage-orange has a limited natural range in the Red River region of east-central Texas, southeastern Oklahoma, and adjacent Arkansas. Indians used to travel hundreds of miles for the wood, prized as the finest for making bows. Then European settlers planted it widely as living fences, taking advantage of the tree’s ability to spread via shoots from lateral roots. But Osage-orange persisted, and became widely naturalized long after the invention of barbed wire rendered them useless to farmers. The tree can now be found in 39 states and Ontario. If Osage-orange does so well elsewhere, why was it restricted to such a small area?