Home » Posts tagged 'pliocene'
Tag Archives: pliocene
Next week is Christmas, Hanukkah started this week, there is Boxing Day, Yule, Kwanzaa, even Festivus and Hogswatch, not to mention the old classic Saturnalia and a whole host of others. Busy week for those wanting to celebrate. In honor of that, I came as close as Arkansas fossils allow to a well-known, traditional, seasonally-associated animal. Were you able to figure it out?
If you guessed reindeer, you were wrong. Sadly, there is no record of reindeer ever having lived in Arkansas that I can find. If there were, I would have used it. So no skeletons of Rudolph for us. The closest thing to a reindeer that has been found in Arkansas are fossils of the common white-tailed deer, which is so common in the state that it not infrequently becomes one with motor vehicles, much to the dismay of both deer and driver.
So what could this be besides a deer, reined or not? Reindeer are in the genus Rangifer, which are in the family Cervidae, along with deer. Cervids are artiodactyls, mammals best known for having cloven hoofs, thus the term “even-toed ungulate.” Unfortunately, Arkansas is not really known for artiodactyls either, other than pigs, and somehow, pigs did not seem an appropriate holiday animal. So what to do?
There is another animal that is often associated with the holidays, especially in the Christmas tradition, that being the donkey. I am sure you’ve heard of the story of Joseph leading a donkey upon which rode Mary to Bethelem and what Nativity scene is complete without a donkey? Donkeys, of course, are in the same genus as the horse, Equus, which are perissodactyls, the odd-toed ungulates. So allow me to introduce you to Scott’s Horse, Equus scotti, named after the paleontologist William Berryman Scott, a Princeton paleontologist known for his work on Cenozoic mammals.
Almost everyone is familiar with horses today. They stand as an iconic symbol of the Wild West, an integral image of the American cowboy and the Native Americans that roamed through the plains. Horses are also one of the most commonly used examples of evolution, with the line from Hyracotherium to Equus in virtually every evolution textbook ever written. All the discussions talk about how they got bigger and lost most of their toes as adaptations for running, and grew higher-crowned teeth to deal with the tough grasses they started to eat that replaced the softer, lush forest plants.
What is less well known outside of those who study evolution and paleontology is that this process was not a straight chain from tiny, forest-dwelling horse ancestor to the modern horse. The horse lineage diversified, evolving into multiple niches. This shouldn’t really be too much of a surprise, considering the diversity seen in horses today, with everything from burros and Shetland ponies to Clydesdales and zebras. Most of them died out before the modern horses we see today arrived. Scott’s horse was one of these extinct forms.
Another thing that is not well known outside of paleontologists is that the modern horse originated in North America, but are not the ones living here today. Horses evolved during the Pliocene, five million years ago. Adaptations allowed them to survive the change from forests to more open, grassy plains, driving their evolution. From North America, they spread into South America through Central America and into Asia and Europe across the Bering land bridge. The Bering Sea Straits were dry at this time because the ice ages during the Pleistocene lowered water levels, allowing passage between the continents. Horses, along with many other animals, like mammoths and camels (also originally American), crossed through the land bridge to populate lands on either side.
At the end of the ice ages about 11,000 years ago, every species of the American horse, including E. scotti, died out, along with all of the other megafauna. Horses continued to thrive in South America and Eurasia, but for over 10,000 years, their North American homeland was barren of horses. It was not until the Spanish conquistadors brought them back that horses once again thrived in North America. Thus, we can thank the Spanish for bringing back a quintessentially American product.