Two Pleistocene Carnivore Dens Near Miami, Florida (Part 2)

Scientists unearthed thousands of bones from the Cutler Hammock site during the mid-1980’s.  The fossils were identified, catalogued, and sent to the University of Florida Museum.  Many of the specimens remain unstudied in detail, and this rich assortment offers an opportunity for paleontologists looking for research material.  The site itself was not completely excavated and is potentially available for future study.  Originally, it was a cone-shaped sinkhole cave filled with sediment, rocks, and fossils. The lower half was below the water table.  The suface was 5 meters by 6 meters wide and from 3 meters to 5 meters deep in various places.  Workers bulldozed sand over the unexcavated section, making it easy for future scientists to re-dig but protecting it from unauthorized fossil hunters.    It’s located on land that is part of Deering Estate Park–a protected environmental, historical, and archaeological preserve of 444 acres in extent.  The preserve is a rare natural area within the suburban sprawl of Miami, Florida and includes endangered pine rocklands, tropical hardwood hammock, mangrove woods, and salt marsh.

The Deering Estate.  Deering was an industrialist who decided to protect his estate from development in perpetuity.  The Cutler Hammock fossil site is located on this property.

Gary Morgan and Steve Emslie studied many of the large vertebrate bones found at Cutler Hammock, and they wrote the paper from which I mined most of the information I used for this blog entry.  They noticed a high number of bones here had gnaw marks on them and concluded this former cave served as a carnivore den during the Pleistocene.  The most common large carnivore fossils found at this site were from dire wolves (Canis dirus), totaling 42 individuals.  This is the third largest dire wolf assemblage in the world behind the La Brea Tar Pits and San Josecito Cave in Mexico.  They also found bones from 9 spectacled bears (the extinct Tremarctos floridanus), 5 coyotes (Canis latrans), 4 jaguars (Panthera onca), 3 bobcats (Lynx rufus), 1 sabertooth (Smilodon fatalis), 1 American lion (Panthera atrox), 1 cougar (Puma concolor), and 1 black bear (Ursus americanus).   The authors of the study suggest the cave was a rendezvous site for packs of dire wolves and not a place where pups were birthed.  They speculate the cave was near a source of water that attracted various prey species.  In another paper Gary Morgan mentioned that the coyote fossils found at Cutler Hammock were unusually small.  Some think they may actually belong to dogs (Canis familiaris) brought by man.  If so, it’s possible the bones may be from yellow dogs, the American dingos, which readily revert to the wild state and are capable of surviving without humans.

Photos of deer and peccary bones gnawed by dire wolves at the Cutler Hammock site.  Click to enlarge. From the below referenced paper.

Photo of dire wolf lower jaw and dire wolf teeth found at the Cutler Hammock site.  Click to enlarge.  Also from the below referenced paper.

Most of the bones from prey species have puncture marks–a telltale characteristic of canid gnawing.  The extinct long-nosed peccary (Mylohyus nasatus) was the most common victim of dire wolves, numbering 75 individuals of which one-third were juveniles.  Horses were the next most common dire wolf victim, though 17 of the 19 individuals were juveniles.  Next in descending order of abundance were white-tailed deer, bison, llamas, and 1 mammoth that was probably scavenged.

Tremarctos floridanus was a close relative of the extant spectacled bear (Tremarctos ornatus) of South America.  Spectacled bears are primarily vegetarian but occasionally eat meat.  Bones scavenged by bears show recognizable differences from bones scavenged by canids.  None of the Cutler Hammock bones show evidence of bear gnawing.  (Hint to professional paleontologists: the authors of this study didn’t examine the bones for evidence of big cat gnawing.  It’s a potential topic for future research.)  Scientists also found bones from mastodon, Harlan’s ground sloth, and the pampathere (a 300 pound grass-eating armadillo) at Cutler Hammock but these showed no evidence of being gnawed upon.

A hearth and bones from 3 adult and 2 juvenile humans (Homo sapiens) were found just above the level where Pleistocene fossils were found.  This material dates to ~11,100 calender years BP.  A human bone found associated with dire wolf bones (in situ) was found as well.  The radiocarbon dating on this bone is considered unreliable.  It’s possible this human bone is as old as the dire wolf bones.  However, there has been much bioturbation at this site.  Land crabs dig holes in this locality, and their actions can mix bones of different ages together.  Or humans may have buried the corpse into the fossil deposit.  Nevertheless, this human bone has dire wolf gnawmarks on it–evidence this person was scavenged (or even killed) by dire wolves.

The below referenced article lists all the vertebrate species identified from Cutler Hammock, and as I read through the list, I noticed a few interesting bird species I neglected to mention in my discussion from part 1 of this blog entry.  The extinct hawk-eagle (Spizaetus grinnelli) flew the skies of Pleistocene south Florida.  It was larger than its closest living relative, Spizaetus ornata.

South American hawk-eagle.  It some times takes prey 5 times its size.  A bird like this lived in Ice Age Florida.

An extinct species of caracara (Milvago reidei), closely related to the living yellow crested caracara, also of South America, lived on the open plains of Florida then.  Passenger pigeons (Ectopistes migratorius) must have occasionally darkened the skies.

The Monkey Jungle Hammock site is thought to have been a carnivore den site as well but as far as I know no study has been conducted on the morphology of bones found there (Another hint to paleontologists.)

Reference:

Emslie, Steve; and Gary Morgan

“Taphonomy of a Late Pleistocene Carnivore Den in Dade County, Florida”

Late Quaternary Environments and Deep History: Tributes to the Career of Paul Martin

Edited by David Steadman and Jim Mead

Hot Springs South Dakota Inc. Reasearch Papers Volume 3 1995

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Bearzilla: The Biggest Bear in History

With a massive presence and a terrifying roar Arctotherium angustidens rampaged over South America about 2 million years ago, chasing frightened predators away from their kills and gorging itself on the scavenged meat.  These giant bears reached a weight of 3500 pounds, so to sustain this bulk, they needed to eat approximately 50 pounds of meat per day.  They occasionally captured wounded or sick prey animals, and they likely consumed some vegetable matter, but their primary survival strategy was “kleptoscavenging.”  Like their distant North American cousins, the giant short-faced bear (Arctodus simus), Arctotheriums trotted long distances, covering grand territories, and with their keen sense of smell they could detect the scent of blood from miles away.  They followed their nose to the source and used their great size to intimidate big cats, wolves, and terror birds from the meat those successful carnivores had worked so hard to procure.

Size comparison between Arctotherium angustidens and Homo sapiens.  This was probably the biggest species of bear in earth’s history.

The bones of an old male Arctotherium were discovered in 1935 during the construction of an hospital in La Plata, Argentina.  The skeleton was not described in the scientific literature until 2010.  The scientists re-examing the specimen determined the individual suffered and recovered from several injuries, likely incurred from battling other male bears.  The old bear also had arthritis.  From the bones they estimated a mass of 3500 pounds.

By about 800,000 BP Arctotherium angistidens no longer occurs in the fossil record.  Some scientists suggest it became extinct due to competition from other predators, but I disagree with this notion.  Instead, I think they evolved into a more herbivorous bear because of environmental changes.  A large “kleptoscavenger,” like Arctotherium, can only survive in an environment with abundant prey animals and predators.  Grasslands can support this kind of biomass, but forests don’t.  I propose that cyclical climatic conditions caused South American grasslands to convert to woodlands.  Arctotherium angistidens was forced to eat more vegetable matter in this woodland environment and eventually evolved into different species, culminating in Arctotherium wingei.  The latter species was as herbivorous as its distant cousin, the still extant spectacled bear (Tremarctos ornatus) and was adapted to live in a similar forested environment, until it went extinct at the end of the Pleistocene.

Bears, cats, and wolves invaded South America when the Central American landbridge rose above sea level 3 million years ago.  The South American versions of bears and saber-tooths initially grew larger than their North American cousins, perhaps because prey animals were larger and slower here.

Arctotherium was in the same family as the North American short-faced bears which included the giant short-faced bear (Arctodus simus), the lesser short-faced bear (Arctodus pristinus), and the Florida spectacled bear (Tremarctos floridanus).  The lesser short-faced bear was probably ancestral to the giant short-faced bear.  The giant short-faced bear was mostly carnivorous but ate some plant matter, while the spectacled bear was mostly herbivorous but ate some animal matter.  A. pristinus was more of an omnivore than the other 2 species.  Fossils of the giant short-faced bear and the spectacled bear have been found at late Pleistocene sites in southeastern North America, but the latter is far more abundant.

Photo from a 1960 issue of Sports Illustrated of the hunter standing next to the taxidermic mount of the biggest wild polar bear ever recorded.  He shot and killed it in Alaska. It weighed 2210 pounds.  This was about the average size of the extinct giant short-faced bear.

Scrape marks on the side of Riverbluff Cave, Missouri.  They are 15 feet high and were made by the giant short-faced bear.  The bear stood 12 feet tall on its back legs and must have reached up with its arms over its head to reach that height.

Size comparison between the giant short-faced bear and a Yellowstone grizzly.

As the top above photo shows, the largest wild polar bear ever recorded was shot in Alaska in 1960.  It weighed 2210 pounds.  This was only slightly larger than an average male giant short-faced bear.  I’m sure a few individuals of the latter species exceeeded that size.  They reached that great size from a combination of genetics and a high protein diet.  Scientists estimated  the giant short-faced bear required 35 pounds of meat everyday.  In environments with fewer prey animals, they may not have reached a particularly large size.  Grizzly bears (Ursus arctos) are the exact same species as the Kodiak bear.  The former average about 500 pounds, yet the latter reach weights of 1500 pounds.  Kodiak brown bears enjoy a high protein diet rich in salmon, while grizzly bears are forced to survive on roots, berries, rodents, and only the occasional scavenged kill.  A Yellowstone grizzly cub, if moved to Kodiak Island, would probably grow much larger on a diet of all the salmon it could eat than it would if it stayed in Yellowstone.  The largest brown bear in captivity grew to 2100 pounds–a mass equal to the average weight of a giant short-faced bear.  This bear had a more favorable diet in its zoo environment than it would have in the wild.

See also: https://markgelbart.wordpress.com/2011/03/10/pleistocene-bears-of-southeastern-north-america/

Reference:

Soibelzan, L.H.; B.W. Schubert

“The Largest Known Bear, Arctotherium angustidens, from the early Pleistocene Pampan Region of Argentian with a Discussion of Size and Diet in Bears”

Journal of Paleontology 85 (1) 69-75 2011

Pleistocene Bears of Southeastern North America

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.