The whitetail deer is probably the oldest large mammal species in North America. Some whitetail deer fossils found in Florida date to an astonishing 3.5 million years BP. By contrast Homo sapiens as a species is roughly 200,000 years old. Whitetail deer evolved from a similar species known as Odocoileus brachyodontus that existed from about 3.9-3.5 million years BP. O. brachyodontus had different teeth and antlers from O. virginiana, but otherwise was a similar animal. The direct ancestor of O. brachyodontus is unknown, but it was probably a species closely related to the Eurasian roe deer that crossed the Bering landbridge during the late Miocene. As far as I know, a genome wide study of the deer family has yet to be completed. The roe deer is the Eurasian species anatomically most similar to the Odocoileus genus, and therefore most likely to share a common ancestor.
Deer ecologically replaced the slender 3-toed species of horses and the American rhinos that formerly occupied the browsing niche in forested environments during the Miocene. Ice Ages began occurring early in the Pliocene, and deer were better adapted to the resulting environmental changes than 3-toed horses and rhinos. South of the ice sheets, a once year round climate of warm temperatures deteriorated to cycles of summer/hot and winter/cold patterns. Drought became more frequent. Broad-leafed trees evolved to drop their leaves during long cold winters and during prolonged droughts. Deer were better able to survive in these deciduous forests.
Whitetail deer buck in its summer red coat. This is the time 0f year pioneers collected deer hides and sold them for a dollar, hence the word “buck.”
Whitetail deer in its dull winter coat that helps it blend in a deciduous woods background. Maybe it’s this adaptation that allowed it to survive when 3-toed horses couldn’t.
Whitetail deer thrive in fragmentary forests, explaining why they’ve been successful for so long. Forests in southeastern North America have always been fragmentary. Factors such as fire, windstorms, megafauna foraging, insect damage, plant diseases, and seed consumption create the patchy forest edge environments of constantly changing composition favored by whitetail deer. The teeth of whitetail deer evolved from those of O. brachyodontus to enable them to include more grass in their diet–another advantage over Miocene browsers as the amount of grassland increased when climatic conditions changed.
Contrary to what I’ve read on some websites, during the Pleistocene, whitetail deer were just as widespread as they are today. It is more accurate to say that in some regions they were less common than some now extinct species of megafauna. In south Florida for example long-nosed peccaries apparently were more abundant than whitetails. Llamas and tapirs likely competed with deer for the same resources in forested environments, while bison and horse were more successful in grasslands. But deer were present just about everywhere, and I suspect they were the most common large mammal in the mid-south, even during most of the Pleistocene.
Modern anthropogenic land usage contributes to the fragmentary habitats whitetail deer are so well adapted to. Men converted farmland to wooded suburbs, and abandoned farmland has become second growth forest. Overhunting by man is the only threat to the existence of whitetail deer. Whitetails do reproduce faster than all the extinct species of megafauna that couldn’t withstand human hunting pressure. But in the past, intense human hunting has eradicated whitetail deer populations in many areas. Deer were reported as scarce near large Indian settlements as early as 1704. By the early 20th century deer were almost extinct in Georgia, but deer from the Great Lakes region were re-introduced here, and with proper management practices they remain abundant. When I go jogging in my neighborhood I see fresh tracks daily, and I see deer sprint in front of me about once every 6 weeks. Some hunters complain deer are becoming less common, and they’re quick to blame coyotes. I think the DNR needs to take a second look at the annual limit which is now up to 10. 30 years ago, the limit was just 3. I find it ironic when hunters shoot 10 deer on their property, then wonder why they don’t see any deer the next year. “It’s the coyotes,” they say. Couldn’t it have something to do with the overgenerous season limits?
Whitetails are outcompeting mule deer (Odocoileus hemionus) in parts of the west undergoing suburbanization. The latter prefer unbroken wilderness rather than the fragmentary habitat favored by their close relatives. Mule deer evolved from an isolated population of whitetail deer some time during the early Pleistocene. Some scientists proposed that the mule deer is a recent species resulting from a hybridization of blacktail and whitetail deer, but the fossil record and genetic studies debunk this hypothesis. There are distinct fossils of mule deer dating to the mid-Pleistocene of California. Moreover, studies of mule deer genetics show that blacktails and mule deer are the same species, despite sporting marked differences in physical appearance. During the Last Glacial Maximum the Cordilleran Glacier separated mule deer from West Coast blacktails for thousands of years, accounting for the different physical traits, but they are still considered the same species by most experts.
Incidentally, Bjorn Kurten mentioned Pleistocene mule deer fossils found in Arkansas. This is about 100 miles east of the species’ current range. Whitetails are the only deer species found throughout the south, but the fossil record shows that elk (Cervus elephus), caribou (Rangifer tarandus), and the extinct stag-moose (Cervalces scotti) ranged into the mid-south during the Pleistocene. Elk likely inhabited grassy hilltops in the piedmont region of Georgia until about 1760. Elk fossils have been found as far south as Charleston, South Carolina. Caribou fossils have been recorded from north Mississippi, north Alabama, north Georgia, the continental shelf off the coast of North Carolina; New Bern, North Carolina; and Charleston, South Carolina. Most caribou fossils found in the south date to the Last Glacial Maximum, but 1 specimen came from interglacial strata. In the primeval wilderness of the Pleistocene there were probably a considerable number of stragglers that broke from huge herds located farther to the north, and these stragglers often wandered south. There were no manmade barriers stopping them. Fossils of the stag-moose have been found in Charleston, South Carolina and north Mississippi. Elk, caribou, and stag-moose never could colonize the lower south and Florida because winters were too short and mild to limit the populations of blood-sucking insects that weaken northern species of deer.
Mule deer. During the Pleistocene they ranged as far east as Arkansas. Unlike whitetails, they prefer unbroken wilderness.
Elk. William Bartram found elk bones on a grassy hilltop that I believe is located in Columbia County just above Augusta. See http://markgelbart.wordpress.com/2013/01/01/a-serpentine-barren-in-georgia-burkes-mountain/
Woodland Caribou wandered south, especially during the Last Glacial Maximum when stragglers broke off from huge herds migrating south of the ice sheets in what is now southern Ohio, Kentucky, and Pennsylvannia.
Replica skeleton of a stag-moose, aka elk-moose. Neither common name is accurate. It wasn’t closely related to either elk or moose. I prefer calling it the giant stag deer. It was slightly bigger than a modern day moose.
South American red brocket deer. All South American deer likely evolved from whitetails. There’s no convincing evidence that any South American deer species ever lived in North America, though a member of the fossil forum claims he may write a paper about material he found in Florida that can be attributed to a South American species.
I used to think an additional extinct species of deer populated the upper south–the stilt-legged deer (Sangamona fugitiva). But scientists analyzed the remains attributed to this species and determined all the material came from whitetails or elk. Sangamona fugitiva is no longer considered a valid species, and as I related last week, fossil remains of marsh deer in Florida are probably from an incorrectly identified whitetail.
All South American deer probably evolved from whitetail deer. Andean mountain deer, marsh deer, brocket deer, and pudus became geographically isolated from whitetails. The latter do range into northern South America, but environmental change throughout the Pleistocene isolated the original populations of whitetails further south in the continent, resulting in varied speciation. Dry climatic phases isolated tropical forests, causing them to become separated by vast grasslands and wetlands, and isolated populations of whitetails evolved into different species.