Posts Tagged ‘ursus americanus’

A Polar Bear (Ursus maritimus) Fossil in Breck Smith Cave, Kentucky?

September 16, 2012

Several old publications mention a polar bear fossil that was found circa 1916 in Breck Smith Cave which is 8 miles west of Lexington, Kentucky.  Apparently, 3 women who were exploring the cave discovered the bones, and they took them to an “authority” at the University of Kentucky. He identified them as polar bear.  Unfortunately, the specimen was never described in the scientific literature, and as far as I can determine, the ownership of this unique fossil has long been forgotten.  Because the presence of polar bears in northern Kentucky would have interesting ecological implications, I would like to locate the fossils and have a modern expert examine them.  If anyone knows where they are, please contact me.

Polar bear killing a seal.  If the fossil specimen from Breck Smith Cave was correctly identified, seals must have also been present in the Ohio and upper Mississippi Rivers during the Ice Age.  Walrus fossils have been excavated from 2 sites in Michigan.  As far as I know, those are  the closest pinniped fossils to Breck Smith Cave.

From the available information I don’t know for sure who the “authority” was that identified the polar bear fossil (or fossils), but I suspect it was Arthur Miller, head of the Kentucky University Geology Department from 1892-1925.  I strongly suspect he misidentified the specimen because the associated fossils imply a temperate environment.  Bones of raccoon, gray fox, woodchuck, wolf, bison, and man were found in the cave with the supposed polar bear fossil.  Today, polar bears are exclusively found in arctic marine environments.  I think it’s more likely the specimen is from a grizzly bear (Ursus arctos) or even a black bear (Ursus americanus).  Grizzly bears are closely related to polar bears and occasionally interbreed with them in the wild and in captivity.  A grizzly bear fossil was found at Welsh Cave as I related in my last week’s blog entry about the Kentucky Bluegrass Country.  However, there must have been a specific diagnostic feature for the scientist who identified the specimen to suggest the fossil specimen was from a polar bear.  Polar bears are almost entirely carnivorous, and their teeth are quite different from those of grizzly and black bears.  If he made the diagnosis based on teeth, he may have been correct.  There’s also the slight possibility that a man carried the polar bear fossil from the arctic to Kentucky.  Maybe he considered it a magic talisman of the great white bear.

Let’s assume the identification is correct, and it was not carried for a thousand miles by people traveling from the arctic to Kentucky.  How did polar bears, a species that depends largely on seals and whale carcasses, live in northern Kentucky?  Even during the Ice Age, northern Kentucky was not exactly polar bear country.  The Laurentide Glacier reached southeastern Ohio during the Last Glacial Maximum, but northern Kentucky was mostly prairie with fingers of boreal forests then.  Glacial advance during the Illinois Ice Age 100,000 years earlier than the most recent one was greater but still barely reached the Ohio River.  If polar bears did range into northern Kentucky during the Ice Ages, seals, their favored prey, must have been present on the Ohio and upper Mississippi Rivers.  Fossil hunters may want to look for seal specimens on the river bottoms here.

It’s not surprising that a scientist could have misidentified fossils from the Ursus genus.  Recent studies of the Ursus genome show a close relationship between black bears, grizzly bears, and polar bears.  (Grizzly bears and brown bears are one and the same species.) The first study of polar bear DNA determined they diverged from grizzly bears ~130,000 years ago.  Coincidentally and conveniently, this corresponds with the earliest known polar bear fossil which is from Norway and dates to ~130,000 BP.  A second study of polar bear DNA wasn’t as convenient–it suggested polar bears diverged from grizzly bears closer to ~600,000 years BP and as a species was much older than from what’s known in the fossil record.  Polar bears live in an environment where fossils are rarely found.  Most arctic fossils are deeply emerged in frigid waters, probably never to be found.  The most recent study of Ursus genetics looked at the whole genome, and it paints a much more complicated picture.  This study found that grizzly, black, and polar bears all diverged from a common ancestor between 4-5 million years ago.  This corresponds temporally with the beginning of the Pliocene when Ice Ages began occurring, causing continental changes in the environment and creating differentiating habitats for new species of bears.  Though black bears and grizzly bears diverged ~5 million years ago, the genetic evidence indicates these 2 separate species occasionally interbred until about 100,000 BP.  The genetic evidence also indicates that although grizzly bears and polar bears diverged as long ago as 5 million BP, these 2 species have periodically interbred in the past and they still do.

A second generation polar bear-grizzly bear hybrid.  A genome wide study suggests grizzly  and polar bears diverged about 5 million years ago but periodically interbreed.  The genome of brown bears living on the Alexander Islands in Alaska is made up of 5%-10% polar bear DNA.  Curiously, grizzly and black bears also diverged about 5 million years ago and periodically interbred until about 100,000 years BP.  Maybe that explains why Pleistocene black bears were as big as modern day grizzlies.

Polar bears probably interbreed with grizzly bears more frequently  during phases of global warming when their favorite habitat shrinks, and they come into contact more often.  Hybrids raised by grizzly mothers have a greater chance of survival because they learn to survive in a more varied habitat.  Middle Pleistocene polar bears were more genetically diverse than they are today, perhaps because the cycles between Ice Ages were shorter during this time period than they were in the Late Pleistocene.

References:

Brown, Joseph Stanley

GSA Bulletin 33 1922

Cooper, C.L.

“The Pleistocene Fauna  of Kentucky” within The Paleontology of Kentucky edited by W.R. Jilson

The University of Kentucky Press 1931

Webb, Miller et. al.

“Polar and Brown Bear Genomes Reveal Ancient Admixtures and Demographic Footprints of Past Climate Change”

PNAS 2012

http://www.pnas.org/content/109/36/E2382/1

Pleistocene Bears of Southeastern North America

March 10, 2011

Nothing demonstrates wilderness more than a robust population of free roaming bears.  During the Pleistocene before people were around to kill them and destroy their habitat, there must have been tens of thousands of bears living within the boundaries of what today is Georgia.  It’s possible that 5 different species could have been found here in the same time span, though we can be more sure there were at least 3 sharing the same range.  Today, only 1 species of bear resides in Georgia–an estimated 5100 black bears still roam the mountains, the Okefenokee Swamp, the Altamaha and Ocmulgee river bottoms, and Houston County.  Occasional stragglers leave these last strongholds and raid urban dumpsters and suburban bird feeders, but these occurrences are rare.  One study of Georgia bears determined that suitable habitat can support 1 bear for every 3 square kilometers.  That means ideally, Pleistocene Georgia hosted a population of 30,000-40,000 bears.  (*Georgia is about 60,000 square miles. 1.86 square miles =3 square kilimeters.  Moreover, during stadials Georgia’s land mass increased by about 10,000 square miles due to the fall in sea level.)

Here’s a review of every known bear species that lived during the Pleistocene in southeastern North America.

Black bear–Ursus americanus

Photo from google images of a black bear in the Okefenokee Swamp.

Ursus abstruscus is the probable evolutionary ancestor of American and Asian black bears which once consisted of a geographically continuous population.  Glacial ice separated the two populations at the beginning of the Pleistocene, resulting in two different species.  Bjorn Kurten notes that Pleistocene black bears grew as large as modern day grizzlies.  I believe Pleistocene black bears were larger and fiercer than their modern day descendents because they had to survive confrontations with saber-tooths, giant panthers, jaguars, and packs of dire wolves.  Cavers and scientists discovered black bear fossils at Ladds and Kingston Saltpeter Cave in Bartow County, and the Isle of Hope Site in Chatham County.  They’re also commonly found in Florida fossil sites but only a few have been recorded from South Carolina.

Florida spectacled bear–Tremarctos floridanus

Photo of a spectacled bear, Tremarctos ornatus,  from google images.  This is the only living species from the once widespread short-faced bear family.  It is a close relative of the extinct Tremarctos floridanus.  Of course, scientists have no way of knowing whether Tremarctos floridanus was also spectacled, but they call it that anyway.

Now extinct, this was likely the second most common species of bear in southeastern North America during the Pleistocene.  Only 1 specimen has ever been recovered in Georgia (at Ladds), but its fossils have commonly been found in Florida and South Carolina.  It’s thought of as primarily a vegetarian, but a recent study of Pleistocene bears concluded that all were opportunistic omnivores that would eat anything they could obtain.  Tremarctos’s range in the late Wisconsinian Ice Age seems to have been restricted to the southeast.  During warm interglacials it expanded as far north as Kentucky.  It probably just lived in the coastal plain of Georgia and South Carolina as well as Florida during colder climatic stages.

Lesser short-faced bear–Arctodus pristinus

Photo of a fossil jaw bone of Arctodus pristinus from Additions to the Pleistocene Mammal Fossils of South Carolina, North Carolina, and Georgia by Albert Sanders.

Photo of fossil bear teeth from the above mentioned publication.

It’s unclear from the fossil record whether this species co-existed with its larger cousin, the giant short-faced bear, or was simply ancestral to it.  Its fossils have only been recovered from a few eastern sites in Florida, South Carolina, Maryland, and West Virginia.  Teeth attributed to this species overlap in size with those of Arctodus simus.  Florida fossils of this species, including those from Leisey Shell Pit, indicate this animal lived from the early to mid-Pleistocene (~1.8 million-300,000 BP), whereas giant short-faced bear fossils in Florida date to the late Pleistocene (~300,000-~11,000 BP).  However, fossils of the lesser short-faced bear were found in South Carolina sediments thought to date from the Sangamonian Interglacial (~132,000-~118,000 BP) which is also considered late Pleistocene.  These South Carolina specimens haven’t been radiometrically dated, so no one knows exactly how old they are.  Perhaps this species did survive as a relic species in some geographical locations until the megafauna extinction.  Arctodus pristinus is considered more of a general feeder; Tremarctos floridanus a more herbivorous species; Arctodus simus a more carnivorous bear.

Giant short-faced bear–Arctodus simus

Dan Reed’s photo-shopped reconstruction of a giant short-faced bear.   

The giant short-faced bear ranks up there with mammoths, mastodons, ground sloths, and saber-tooths as among one of the most spectacular creatures of this era.  Studies suggest it lived by aggressive scavenging.  It’s extremely acute sense of smell detected blood from a great distance.  Then, the beast would relentlessly trot toward the source of the appetizing odor, and its sheer size would intimidate the partially satiated carnivore that actually made the kill into surrendering the carcass.  Arctodus simus fossils are more common in western fossil sites, but a few have been discovered in the southeast, proving it did occur here, at least sporadically.  An Arctodus simus skeleton rested in the Fern Cave system in Jackson County, Alabama which borders northwestern Georgia, until it was discovered by cavers in 1970.  In addition a number of teeth from this species have recently been discovered in north Florida fossil sites, and some Arctodus simus material was also discovered in Virginia.

Grizzly bear–Ursus arctos

Photo of a grizzly bear and cub from google images.

Welsh cave in Kentucky yields grizzly bear fossils dating to about 12,000 BP.  This is the easternmost known occurrence of this species.  Grizzly bears roam hundreds of miles, so it’s likely if they lived in Kentucky then that they must have entered Tennessee.  But the lack of grizzly bear fossils in other southeastern states suggests they never penentrated the region in significant numbers.  Still, I believe a few irregular stragglers may have wandered into what’s now north Georgia.  It may be that the existence of 3 or 4 other species of bears prevented grizzly bears from colonizing much of the southeast during the Pleistocene, and then man arrived, creating another obstacle blocking their migration into the region.  Grizzly bears are a relatively recent addition to North America’s mammalian fauna, but they did live on the continent prior to the LGM, 30,000 years BP.  They’re the same species as the Eurasian and Alaskan brown bears.

If I could live in the Pleistocene (part 4).

For those unfamiliar with this blog, I occasionally fantasize living during the Pleistocene but with modern conveniences, such as an adobe house with woodstoves, solar heating, electricity, and a time tunnel that connects me to the modern world.

I’ve thought of a simple way to observe bears from my abode.  Connected to my Pleistocene house is a 5 story watchtower designed in the shape of a lighthouse in which I can view the surrounding landscape.  I would take a barbecue grill to the fifth story which has a canopy but an open window stretching for 360 degrees around.  There, I would grill meats.  The aroma should attract bears and other carnivores from miles around.  A bear could potentially climb up the side of a light-housed shaped building, so I would have to have some kind of designed guards that would prevent this. 

I would avoid hunting bears, if possible.  I think modern hunters who kill bears are jerks.  I can understand why the pioneers did it.  They didn’t have grocery stores and had to eat and make use of what they could obtain.  But there is no reason to hunt bears today, unless they prove a danger to tourists.  They don’t reproduce as rapidly as deer, and it’s just not ecologically necessary to hunt them.

Bears were a valuable source of meat and fat for early settlers.  Early accounts reveal an important dish of the Indians.  The Indians frequently diced up venison (which is very lean) and fried it in bear fat.  Bear fat was also the number one source of cooking fat in New Orleans in 1800.  It was gradually replaced by lard as the settlers brought in hogs.