The Presence of Caribou in Southeastern North America during the Pleistocene and it Paleoecological Implications

 

The reindeer, legendary conveyor of Santa’s sleigh, is an Holarctic animal, meaning it lives south of the Arctic Circle in both North America and Eurasia.  In North America the reindeer is more commonly known as caribou.  When Europeans colonized the New World caribou lived as far south as upstate New York, but today their range in North America is restricted to Canada and Alaska.  During Ice Ages, however, almost all of their present day range was under glaciers–unsuitable habitat even for such a cold hardy animal.  Caribou range shifted south then, and caribou fossil material has been found at numerous southeastern sites including Bell Cave in Alabama, Yarbrough Cave in Georgia, 3 caves in Tennessee, off the North Carolina coast, off Myrtle Beach, and in Charleston, South Carolina (the most southeastern known occurrence).  Apparently, caribou occurred at least as far south as the piedmont region.

Reindeer and Caribou are the same species.

Caribou fossils have been found associated with an interesting mix of species at the above-mentioned fossil sites, though it’s unclear if they all lived at those localities during the same climatic phases.  Cave and offshore sites can collect the bones of animals from many different time periods.  Nevertheless, caribou bones have been found with the remains of giant beavers, flat-headed peccary, long-nosed peccary, woodland muskox, white tail deer, stag-moose, horse, tapir, mastodon, ground sloth, jaguar, and dire wolf.  Pleistocene caribou in eastern North America likely preferred open spruce woodlands interspersed with prairies.  This habitat would have also been favorable for horse, flat-headed peccary, bison, and mammoth.  By chance caribou remains haven’t been found with the latter 2, but they probably co-occurred at some locations.  Dire wolves, habitat generalists, likely co-occurred with caribou as well and probably preyed on them.

Baker Bluff Cave in northeastern Tennessee has well stratified deposits that contain many vertebrate bones from 2 different climate phases.  Information from this site can help determine the faunal composition that co-occurred with caribou.  The oldest deposits at Baker Bluff Cave are interpreted as representing a temperate forest consisting of oak, northern pine, birch, beech, etc.  Gradually, this environment gave way to the open spruce woodland/prairie as the climate became colder and drier during the Last Glacial Maximum.  White-tailed deer remains are abundant throughout all layers of the deposit, and they co-occur with caribou in Canada today, so undoubtedly they were a contemporary of Pleistocene caribou.  Long-nosed peccary, a forest edge species, like white-tail deer, likely co-occurred with caribou as well.  Mastodon, giant beaver, and stag-moose inhabited wetland environments adjacent to caribou habitat, and I’m certain they were contemporaries with caribou.  Woodland musk-ox, another likely contemporary, foraged in shrub habitat near caribou range.

A jaguar tooth found at Baker’s Bluff Cave was excavated from the lowest oldest level.  This is evidence Pleistocene jaguars inhabited cool temperate forests, but it seems unlikely they survived in the region when the forest gave way to boreal environments.  However, caribou may have also occurred in the southeast during interstadials.  (Good carbon-dating of regional caribou fossils has yet to be conducted.)  It’s impossible to determine from available data whether jaguars inhabited the same range as caribou.  The same can be said for the tapir, a species that preferred thick forest.

Cave deposits contain an even greater abundance of small vertebrate fossils.  Most smaller animals are more restricted to certain environments than larger species, and their composition better reveals what natural communities of this locality were like.  The Baker Bluff Cave deposits are particularly interesting.  Fossil material of species still found in the region today (gray squirrels, eastern chipmunks, southern flying squirrels) were present throughout the deposit but were less common during the open spruce woodland/prairie phase.  By contrast some species that today live to the north and west of the region (13-lined ground squirrels, least chipmunks, northern flying squirrels, badgers, pine martens, fishers, magpies) were also found throughout the deposit but were less common during the cool temperate forest stage.  Red squirrels were also less common during this phase but more common after the landscape changed.  Fossil remains of 13-lined ground squirrels have been excavated from sites throughout the southeast but no longer occur east of the Mississippi.  Fossil material of birds that prefer open spaces such as upland sandpiper and prairie chicken were excavated from Bell Cave and Yarbrough Cave.  The presence of these species is evidence prairie habitat was common in the region during Ice Ages.  Pine marten specimens, dating to the Pleistocene, were discovered as far south as northern Alabama, and Pleistocene fisher specimens turned up in northern Alabama and north Georgia.  This is evidence of boreal environments in the upper south.

I hypothesize Ice Age ecosystems in southeastern North America were more diverse than they are today due to rapid climate fluctuations.  Climate phases of warm wet interstadials (but cooler on average than today) and cold arid stadials alternated but the response of the floral and faunal composition to these rapid climate changes lagged behind.  Some climate phases lasted for a few thousand years or perhaps just centuries or even decades.  They weren’t long enough to completely eliminate habitat for species with warm temperate affinities, nor did they last long enough to extirpate habitat favorable for species with boreal affinities.  This explains why eastern chipmunks co-occurred with least chipmunks, and why caribou may have shared the range with jaguars and tapirs.  During cold phases though prairie and boreal forest expanded, oak woodlands persisted on some tracts of land, especially south-facing slopes.  During warm phases oak woodlands expanded, but spruce forests persisted on north facing slopes.

Herds of caribou formerly wandered through Georgia followed by packs of dire wolves and prides of lions.  The herds traveled through fingers of prairie between open woods consisting of pine and spruce and oak where turkeys foraged on the ground and fishers chased gray squirrels through the tree tops.  Landscapes of present day Georgia are unrecognizable by comparison.

Reference:

Guilday, John; H. Hamilton, E. Anderson, and P. Parmalee

“The Baker Bluff Cave Deposit, and the Late Pleistocene Faunal Gradient”

Bulletin of the Carnegie Museum 1978

Tags: Baker Bluff Cave, caribou in southeastern North America during the Pleistocene, Guy Wilson Cave, paleoecological implications