Posts Tagged ‘whitetail deer’

The Amazing Adaptable Whitetail Deer (Odocoileus virginiana)

March 5, 2013

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 https://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.

Sabertooth Cave in Citrus County, Florida

February 28, 2013

 

Location of Citrus County, Florida.  My late grandparents used to live in Inverness located on the eastern side of the county.  The Sabertooth Cave fossil site is located near the center of the county.

My late grandparents lived in Citrus County, Florida for about 5 years during the mid-1970’s.  A manmade freshwater canal flowed past the property line of their backyard.  Developers probably dug the canal to connect residential properties with a large natural lake.  If a resident felt like boating on the lake, they had direct access to the water.  I recall enjoying many adventures when our family visited Inverness.  I caught chain pickerel and bullhead catfish in the canal.  I remember being so thrilled that I jumped up and down after landing the pickerel.  For a 10 year old with a self-esteem not unlike that of the comic strip character, Charlie Brown, successfully catching a fish was a big deal.  One day, my father and I paddled a canoe to an island in the middle of the canal.  We disembarked to do some exploring, and I almost stepped on an alligator’s head.  It hissed at me and retreated into the water.  On another occasion my grandfather took the whole family in his big new boat, and it started taking on water.  My mom nervously urged him to turn the boat around.  On my own I explored old grapefruit orchards, and the huge natural lake nearby.  I saw lots of wildlife including ospreys, limpkins, coots, anhingas, a large soft-shelled turtle, and a Florida muskrat which scolded me as I walked along the edge of the canal.

This area of Florida has always been a great place for a boy’s adventure.  In 1928 a group of boys found a natural trap cave not far from Lecanto, a town located in the center of the county.  They explored it, and 1 of the boys found a complete upper left canine of a Smilodon fatalis.  The cave was given the name Sabertooth Cave based on that specimen.

Photo of Sabertooth Cave.  I wonder how the boys explored it.  They must have used a ladder because the shaft is vertical.

The cave is actually a sinkhole trap created when acidic rainwater dissolved underlying limestone causing the ground to collapse underneath.  Animals sporadically fell inside and some birds nested in the sheltered trap, accounting for the fossil accumulation.  By 1928 the cave was accessible to the surface through 2 vertical shafts ranging from 25-40 feet deep.  George Simpson excavated the fossils that same year and catalogued them in the below referenced paper.

I’m researching for a future essay about Pleistocene deer, so I was interested in 1 particular specimen excavated from this site.  The only fossil of a species closely related to the South American marsh deer (Blastocerus dichotomous) was found here.  Based on a lower jaw,  Simpson declared it was a new species–Blastocerus extraneous.  However, in his book Fossil Vertebrates of Florida, Dr. Richard Hulbert expressed doubt that it was a valid species because no more marsh deer bones in North America had been discovered since.  I compared the illustration of the supposed marsh deer jaw bone with 1 from a photo of a white tail deer jaw bone I found on google images.  They look like an exact match.  I inquired about this species on The Fossil Forum website, and an anonymous expert informed me that Simpson didn’t have access to Key deer material for comparison.  The anonymous poster claimed that he did collect road-killed Key deer material for paleontological comparisons, and that the specimen from Sabertooth Cave was from that small subspecies of white-tail deer, not a marsh deer.  Apparently, there was a great divergence in size within the local population of white-tails as early 130,000 years ago.  During this time period marine highstands flooded the keys, and surviving Key deer must have mixed with the general population of deer. The problem with this explanation of the specimen is that marsh deer are slightly larger than white tail deer, not smaller.  Though it would be interesting if South American marsh deer once lived in Florida, I’ve concluded that Simpson was wrong, and the jawbone is just from a regular old white-tail deer.  Judge for yourself from the following images.

Canebreaks 006

An illustration of the jawbone that I believe George Simpson misidentified as coming from a species closely related to the South American marsh deer.  I just don’t see what he was seeing.  Click to enlarge.

Jawbone from a white tail deer.  Looks like a match with Simpson’s illustration.

The specimen Simpson mistakenly thought was from a South American marsh deer, possibly may  be from a Key deer, a small subspecies of white tail deer that mixed in with the general population during marine highstands when small areas of land across the state became isolated from  flooding.  Though the small subspecies often became genetically swamped, the genes for dwarfism remained in the population, allowing the subspecies to become re-established on keys .

Although I think the marsh deer specimen was a bust, Sabertooth Cave produced many exciting fossils typical of the late Pleistocene–Wheatley’s (or Jefferson’s) ground sloth, giant armadillos (pampatheres), mastodon, llama, long-nosed peccary, white tail deer, horse, tapir, capybara, saber-tooth cat, and dire wolf were the large mammal species found.  The smaller mammal species included opposum, beautiful armadillo, mole, marsh rabbit, cottontail rabbit, cotton rat, rice rat, Florida muskrat, gray fox, bobcat, and striped skunk.  Sabertooth Cave is the type locality where fossils of the Florida bog lemming (Synaptomys australis) were first found.  The Florida bog lemming may simply be a large extinct subspecies of the southern bog lemming (Synaptomys cooperi). Scientists aren’t sure. On islands large ungulates become dwarfs, while some rodents grow larger.  It’s possible during marine highstands there were many isolated  islands within vast wetlands.  That would account for key deer and large lemmings in a site located so far inland. Another interesting find at this site was the apparent co-existence of the western species of pocket gopher (Thomomys sp.) with the eastern species (Geomys pinestis).

A western species of pocket gopher from the Thomomys genus.  It lived in Florida during the Pleistocene.

Southeastern pocket gopher.  I think my cat killed 1 of these once but she wouldn’t let me take a close look at it.

Bird fossils unearthed at Sabertooth Cave were diagnosed as being those of a lesser scaup aka bluebill duck, turkey vulture, black vulture, bald eagle, sparrow hawk, barred owl, barn owl, screech owl, bobwhite quail, and turkey.  Some of these birds may have roosted here and dropped prey in the cave.  I think the vultures and eagle were attracted to animals that fell in the cave and died, and the scavenging birds in turn became trapped.  Somehow alligators and turtles fell inside the cave as well.

The species composition shows that the surrounding landscape consisted of freshwater marsh, woodland swamp, and some meadows–similar, if not exactly, the same environment that existed here til the 20th century when man ruined it.  As far as I know, scientist haven’t attempted to date the fossils found here, but most suspect they date to the Sangamonian Interglacial ~132,000-~118,000 BP.

Sabertooth canine from whence this nice fossil site got its name.

Reference:

Simpson, George

“Pleistocene Mammals from a Cave in Citrus County, Florida”

American Museum Novitas 328 October 26, 1928

http://digitallibrary.amnh.org/dspace/bitstream/handle/2246/3110//v2/dspace/ingest/pdfSource/nov/N0328.pdf?sequence=1