Pleistocene Pine Voles (Pitymys pinetorum)

Evolutionary biologists like to study rodent fossils.  Rodents occur in high population numbers, and their rapid generational turnover means evolutionary change occurs faster than with larger slower breeding animals.  Scientists recently studied pine vole teeth from 2 caves in Kentucky and 1 cave in Georgia that date to the last Ice Age and compared them with modern day pine vole teeth.  Pine vole teeth from Hilltop and Cutoff Caves in Kentucky date to about 30,000 years ago, and the pine vole teeth from Yarbrough Cave in Georgia date to about 23,000 years ago.  Pine voles are still a common species, occurring all across eastern North America.  Despite their name, they prefer living in moist deciduous forests where they tunnel under tree roots and feed on roots, seeds, fruit, fungus, and insects.  Their fossorial existence keeps them safe from owls and hawks, though snakes can enter their burrows.  Pine voles are considered arvicolid rodents because their teeth cusps are in the shape of alternating triangles.  Other common arvicolid rodents include meadow voles, lemmings, muskrats, and cotton rats.

Pine voles weigh just an ounce.  They mostly live underground but occasionally venture to the surface.

Pine vole range.  Pine vole is a misnomer.  They prefer moist deciduous woods, not pine forests.  Nobody knows why the common name is pine vole.

The pine vole teeth from the Kentucky Caves show the pine voles living then were the same size as modern day pine voles living in the region.  However, pine voles living in north Georgia during the Ice Age were larger than modern day Georgia pine voles and about the same size as northern pine voles.  Scientists believe this was in response to colder temperatures.  Bergmann’s rule states that animals living in colder climates generally grow to a larger size because they are better able to retain body heat.  The authors of this study can’t determine whether this large size was the result of inbreeding with northern populations of larger pine voles that colonized the region or natural selection of the local population.

Reference:

Martin, Robert; and K. O’Bryan

“Size and Shape Variation in the Late Pleistocene Pine Vole (Mammalia: Arvicolidae: Pitymys Pinetorum) First Lower Molars from 3 Caves in Kentucky and Georgia”

Paludicola September 2014

Colorful Fox Squirrels–Were they the More Common Squirrel in the Southeast During the Pleistocene?

The extinction of the megafauna saddens me.  America’s wilderness areas are devoid of mammoths, mastodons, ground sloths, and so many other animals, and an ungodly long drive is required to see the remaining species such as bison and elk, unless a person is lucky enough to live somewhere near Yellowstone National Park or in Alaska.  But at least squirrels and rabbits are still abundant in most places.  They are every bit as interesting as the extinct species of megafauna and during the Pleistocene the total biomass of smaller animals probably outweighted that of the larger beasts, so they were common then too.

Tree squirrels are relatively rare in fossil sites because they live in wooded habitats.  When they die, their bodies mix with acidic leaf litter which dissolves bones, if a scavenger doesn’t come along and munch them down first.  Thanks to predatory birds, squirrel fossils do occur in cave deposits.  Hawks and owls capture squirrels, carry them to roosting sites in caves, and often sloppily drop pieces of squirrel where the cave environment preserves them.  Yarbrough Cave in Bartow County Georgia yields the remains of 5 squirrel species–woodchucks, chipmunks, gray squirrels, fox squirrels, and 13-lined ground squirrels.  This cave deposit dates to the Last Glacial Maximum (~20,000 BP carbon date average based on 4 sample dates).  The variety of squirrels is evidence of a diversity of habitats.  Gray squirrels prefer young dense forests; fox squirrels like open mature woodlands; chipmunks inhabit boulder-strewn woods; woodchucks live in open meadows; and 13-lined ground squirrels are denizens of prairie.

Although Pleistocene environments in Georgia consisted of many constantly changing stages of succession, I think 0pen mature forests would have been the most common type.  Frequent fires, megafauna foraging, insect infestation, tree diseases, windthrows, and drought eventually convert dense young forests into open parkland environments with widely spaced large older trees lucky enough to survive the ravages of nature.  Gray squirrels are more common today in Georgia because young dense forests predominate, following the clear cutting of yesteryear.  These squirrels escape predation by jumping from tree to tree which is possible in forests with closely spaced trees, but bigger clumsier fox squirrels run along the ground to reach the safety of a tree.  They’re better adapted to open forests.  Therefore, fox squirrels may have been the more common squirrel of the late Pleistocene in the upper south.  (Fossil evidence suggests they didn’t arrive in Florida until very late in the Pleistocene.)

This fox squirrel was recently spotted in Ringgold, Georgia which is in the northern part of the state where fox squirrels are said to be rare to absent.  This proves they still live in this region.  The lady who took this photo didn’t know what this animal was and posted it online.  Notice to college biology students searching for a thesis idea:  No recent study has been conducted on fox squirrel populations in Georgia.

Mounted fox squirrel killed by a hunter in Georgia.  I lifted this and the following photos from the Georgia Outdoor News forum.  Check out their political forum.  They aren’t exactly open to progressive politics. 

Another mounted fox squirrel killed in Georgia by a hunter.  Note the orange color phase.  Fox squirrels in northeastern Ohio are orange but have no white marking on their nose.  Fox squirrels are locally common on the southeastern coastal plain.

 

 

Note all the color variations on these fox squirrels killed in just 1 locality on the South Carolina coastal plain.

In present day Georgia and South Carolina fox squirrels occur locally on the coastal plain.  They are reportedly rare to absent in the piedmont and mountains, though the the top photo proves they’re not extinct in the region.  In the southeast they seem to prefer open pine forests with a few oaks.  Curiously, in the midwest they’re restricted to hardwood forests.  On average they weigh twice as much as gray squirrels and come in a much greater variety of colors.

I grew up in Niles, Ohio, a small town in northeastern Ohio.  Big orange fox squirrels were the only kind of squirrel I ever saw there.  Our house was surrounded by an oak-dominated woods on 2 sides.  Unlike the orange color phase of southeastern fox squirrels, the ones in Ohio had no white marking on their nose.  I also saw gray and black fox squirrels at a park next to Niagara Falls.  In Georgia I’ve only seen a fox squirrel once.  It was a black one among a dozen gray squirrels poaching pecans in a Burke County orchard.  They are reportedly common on golf courses in the South Carolina coastal plain.  I haven’t seen a fox squirrel in 20 years.  I’m trying to determine how I can find some time to scope this species out on a beach trip next month.

Caribou (Rangifer tarandus) in Pleistocene Georgia

It always fascinates me that caribou used to roam what’s now Georgia. The presence of caribou in the Pleistocene south is confirmed from fossil finds in Yarbrough Cave, Bartow County, Georgia; Bell Cave in northern Alabama; Charleston, South Carolina; and at least 3 sites in Tennessee–Baker Bluff Cave, Beartown Cave, and Guy Wilson Cave.  Caribou fossils have not been found in the abundant fossil sites in Florida, so its southernmost range limit occurred somewhere along a line drawn through what’s now middle Georgia, South Carolina, and Alabama.  The present day range of eastern woodland caribou was completely under glacial ice during much of the last Ice Age, so of course, they must have ranged further south.

What a majestic beast.

I have some questions about caribou in Pleistocene Georgia that I suppose may never be answered.  Were they year round residents or did they migrate here seasonally?   Today, barren ground caribou are known for their long distance migrations, but eastern woodland caribou are reported to stay in the same area their entire lives.  Did caribou live in the south during cold phases of climate or were they here during interstadials as well.  The caribou fossil from Charleston, South Carolina comes from strata thought to date to a warm interglacial.  There is a scientific method that can be used to answer the first question.  So far no scientist has chosen to chemically analyze the tooth enamel of fossil bones of southern caribou.  By determining the strontium isotope ratios in the tooth enamel they can compare it to that of extant mammals and mathmatically estimate where the extirpated southern caribou spent their time.  Scientists have used this technique with mastodons and mammoths.  Scientists determined from mastodon fossils found in Florida that they had spent time in central Georgia, but mammoths in Florida did not migrate long distances.

Robert Martin, a professor at Murray State and author of Missing Links: Evolutionary Concepts and Transitions in Time, first identified two caribou molars from Yarbrough Cave.  In an email he informed me there was also unsorted material from the cave but was unclear whether this consisted of more caribou specimens.  Murray State donated all of the fossils to the Florida Museum of Natural History where they probably rest in the bottom of a basement drawer.  The original fossil discoveries were made in 1991 but they have yet to be described in detail in the scientific literature with the exception of a few teeth of southern bog lemmings.  I had to ask Dr. Martin which parts of the caribou they found in the cave. 

Caribou are the only member of the deer family that have antlered females.  Male caribou shed their antlers after the rut is over, but females retain theirs through the winter.  The females dig craters in the snow, exposing lichen and grasses–their food supply.  They defend these territories against other females and antlerless males.  The females with the biggest antlers have the best chance of maintaining their top condition for next year’s pregnancy, and it improves the survival rate for the present year’s calf.  In regions with light snows where it’s unnecessary to dig craters, female caribou have smaller or no antlers.  Therefore, southern female caribou probably had smaller antlers.

For most of the year cow caribou fear or are antagonistic toward bulls.  During the rut the bull caribou approach the cows by lowering their head and bleating like a calf approaching to nurse.  (This reminds me of human foreplay–tit sucking.)  The female will stop and urinate, and the male will smell the urine to test whether she’s in estrus.  The vomerosonal organ in the nostril is used to detect the pheremone levels.  Primates lost this organ along their evolutionary pathway, but humans still wrinkle their noses at funky odors.

Reindeer warble fly.  They lay eggs under the hides of caribou.  Eskimos enjoy eating the larva–a fatty, salty snack, according to R. Dale Guthrie.  Reindeer meat is lean, and the average human would starve on such a high protein diet with no fat.  The warble fly larva provided valuable fat for people living in the Pleistocene.  Reindeer warble flies must have expanded their range into Georgia during the Ice Age.

Reindeer warble flies (Oedenagena tarandi) torment caribou all summer.  Their larva live under the hide during the winter and emerge during the spring.  Caribou meat is a healthy source of protein but is so low in fat that most humans would starve to death if they only ate this kind of meat.  Eskimos and Pleistocene Europeans eat or ate the warble fly larva which is high in fat.  It’s a valuable dietary supplement.  Warble fly larva is even depicted in paleolithic art alongside the more famous cave paintings of mammoth, bison, and horses.  Reindeer warble flies almost certainly enjoyed an expanded range during the Pleistocene and flew in Georgia then.

Yarbrough Cave

The area around this cave is clear cut, and the owner would “just as soon fill the cave in or level it.”  Many real estate developers are ignorant Nazis whose God is money.

View from inside the cave.

Yarbrough Cave is a small one about 120 feet long with a couple of small side passages.  Some woodland Indian artifacts have been excavated here.  All of the Pleistocene fossils in this cave come from a surprisingly small area–a 5 foot square, 6 foot deep hole in a side passage known as the Peccary Room.  The fossils date from between ~15,000 BP-~ 19,000 BP (from 2 different specimens), the end stage of the Last Glacial Maximum.  Like most other Pleistocene fossil sites in Georgia, the species represent a variety of habitats that must have existed nearby–woodlands, grasslands, and wetlands.  13-lined ground squirrels require extensive treeless prairies, but the other 6 species of squirrels show that forests must have been predominant.  Beaver, muskrat, river otter, and raccoon prove wetlands occurred here as well. Many more microfossils were lost here when some nameless blundering scientist botched the removal of a large section of matrix.  He probably lost all the bird bones.  There’s probably more fossils to be found here with a little digging and as I mentioned earlier the fossils already found here have yet to be described in detail.  Anyway, here’s the list of Pleistocene fossils that were excavated from Yarbrough Cave between 1988-1991. * denotes extinct species

short tailed shrew–Blarina brevicauda

least shrew– Cryptotis parva

eastern mole–Scalopus aquaticus

eastern pipistrille-Pipistrelus subflavus

big brown bat–Eptesicus fuscus

*giant ground sloth (probably Harlan’s)–Megalonychid sp.

*beautiful armadillo–Dasypus bellus

rabbit sp.?–Sylvilagus sp.

eastern chipmunk–Tamias striatus

13-lined ground squirrel–Spermophilus tridecemlineatus

red squirrel–Tamiasciurus hudsonicus

gray squirrel–Sciurus carolinensis

fox squirrel–Sciurus niger

southern flying squirrel–Glaucomys volans

northern flying squirrel–Glaucomys sabrinus

woodchuck–Marmota monax

beaver–Castor canadensis

mouse sp.?–Peromyscus

wood rat–Neotoma floridana

pine vole–Microtus pinetoreum

*?steppe vole–Microtus sp.

meadow vole–Microtus pennsylvanicus

muskrat–Ondatra zibethicus

southern bog lemming–Synaptomys cooperi

meadow jumping mouse–Napeozapus insignis

dire or timber wolf–Canis dirus or lupus.  The preliminary report says the fossil material compares favorably to the latter but tooth size overlaps between the 2 species  and I bet it’s from the former.  Ronald Nowak, the world’s foremost authority on Pleistocene canids, doesn’t think timber wolves ever colonized the southeast.

black bear–Ursus americanus

raccoon–Procyon lotor

weasel sp.–Mustela

striped skunk–Mephitis mephitis

river otter–Lutra canadensis

cougar–Puma concolor

bobcat–Lynx rufus

*long-nosed peccary–Mylohyus nasatus

*flat-headed peccary–Platygonus compressus

white tail deer–Odocoileus virginianus

caribou–Rangifer tarandus

References

Guthrie, R. Dale

The Nature of Paleolithic Art

The University of Chicago Press 2006

Martin, Robert

“A Preliminary List of Late Pleistocene Mammals from the Peccary Room of Yarbrough Cave, Bartow County, Georgia”

Palidicola 3 (2) 33-39 May 2001

http://www.forums.caves.org/viewtopic.php?f=8&t=5308

What was the Deer-Hunting like in Pleistocene Georgia?

Deer-hunting season begins in Georgia this month.  The only native species of deer modern hunters can hunt in state is the white tail deer (Odocoileus virginianus) which numbers close to 1.2 million, making it the second most common large mammal in the state, behind man.  This season, hunters are allowed to take an astonishing 10 antlerless and 2 antlered deer, suggesting either a shortage of hunters or an overpopulation of deer.

The fossil record provides evidence that white tail deer were a common large mammal species during the Pleistocene too.  Their bones are found in almost all Pleistocene-dated sites in state.  They’re a species that prefers forest edge habitats, and the dynamic ecosystems of the Ice Age with fire, rapid climate fluctuations, and megafauna  destruction of trees, created extensive areas of this type of habitat.

Photos I took of white tail deer at Fripp Island, South Carolina.  The deer here are numerous and have little fear of humans.  Nevertheless, they should not be approached or fed because they are unpredictable wild animals and dangerous.  They can use their hooves to stomp people.  Deer have been known to kill dogs.

I suspect elk (Cervus canadensis) may have been the second most common kind of deer in what’s now Georgia during the Ice Age, ranging as far south as the fall line between the piedmont and the coastal plain.  Elk fossils from Kingston Saltpeter Cave in north Georgia, and near Charleston, South Carolina are the southernmost record of this species.  None have been found in Florida’s abundant fossiliferous deposits.  I think this is evidence of an abrupt difference in climate between the piedmont region of southeastern North America and the coastal plain.

Scientists don’t know much about the extinct fugitive or stilt-legged deer (Sangamona fugitiva).  It was like a white tail deer but approached an elk is size, maybe being slightly smaller.  The deer lived in east central North America from Missouri to West Virginia and a definitive record comes from Hamblen, Tennessee.  It probably occurred in northern Georgia because Dr. Clayton Ray found a tooth that may or may not have been from this species–the specimen was in too dodgy a condition to identify with certainty.

That caribou (Rangifer caribou) lived in northern parts of southeastern states during the Ice Age fascinates me.  Caribou fossils discovered in Bell Cave, Yarbrough Cave in Georgia, and near Charleston, South Carolina are evidence this species lived much further south than it did in historical times.  Were they stragglers or members of large migrating herds that regularly travelled through Georgia?  I wish I knew.

The stag-moose, or elk moose (Cervalces scotti) is kind of misnamed for it wasn’t closely related to a moose or an elk.  It was named so because it slightly surpassed a moose in size and sported antlers similar to those of the elk.  However, it was a distinct species, now extinct.  Its fossils are occasionally found in places like Ohio or New York.  One tooth of this species was discovered in Magnolia Phosphate Mine near Charleston (as I noted in a previous blog entry about the site)–evidence a small population roamed the upper south.

Pleistocene venison may have had a bitter flavor.  According to pollen records, wormwood (Artemesia) flourished more abundantly in the south than it does today.  This plant still commonly occurs in western localities, such as in Yellowstone National Park.  Reportedly, game that’s been eating wormwood acquires a bitter taste.  I can attest to the fine qualities of wild Georgia white tail deer meat–it tastes like dry beef, and I think the wild venison is better than New Zealand farm-raised animals, which though also good, tastes more like lamb.

Cougars vs. Jaguars

Cougars and jaguars co-existed for at least 500,000 years throughout North America, and today still co-exist in many areas of South America and Mexico.  Both species are adaptable enough to occupy a wide variety of environments, including deserts, lightly wooded savannah, flooded swamps, and tropical rain forests.  They also feed upon many of the same prey species.  This spawns two questions: what ecological differentiation allows two big cat species to co-occur on the same range, and what factors allowed cougars to remain in much of North America where jaguars were extirpated?  A number of scientific studies help solve these ecological mysteries.

Comparison of cougar and jaguar diets

Studies of jaguar and cougar diets consistently show significant differentiation.  Although cougars and jaguars tackle many of the same species, the latter selects for larger sized individuals.  One study of co-occurring jaguar and cougar populations in Venezuala–a region consisting of woodland, savannah, and swamp–found the following differences in prey size selection between the two species.

…………………………………….Cougars……………………………Jaguars………………

Small size prey…………………17%……………………………………1%……………….

Medium size prey……………..31%……………………………………14%……………..

Large prey……………………….52%……………………………………85%…………….

For example in this region collared peccaries are an important diet item for both species, but cougars exclusively take small juveniles, while jaguars take mostly adults and sub-adults.  Both big cats took a wide range of prey species with cougars taking 12 different kinds of animals and jaguars taking 10.  Jaguars preyed more heavily upon capybaras here than cougars did.  Jaguars also preyed upon white-lipped peccaries–an aggressive species that cougars completely avoided.  White-lipped peccaries live in large groups and frequently come to the aid of their comrades and attack predators.  They’ve been known to kill jaguars and even humans.

Illustration by John James Audubon

Another study of jaguar diet, this one in southern Brazil where flooded plains are the predominant habitat, found that the jaguar diet there included 31% cattle, 24% caiman, 21% peccary, 4% feral hog, 3.0% marsh deer, 3.2% giant anteater, 2% capybara, 1.6% brocket deer, and about 10% other.  438 prey items were recorded, showing that jaguars will take what’s generally available.  Incidentally, both jaguars and cougars are capable of killing the alligator-like caiman, but take them less than would be expected based on their abundance.

Illustration by John James Audubon

A third study, this one in Mexico where both jaguars and cougars mostly prey on deer, peccary, and armadillo, also found that jaguars select for larger prey items.  This study concludes that the “cougar’s ability to exploit smaller prey gives them an advantage over jaguars when faced with human-induced habitat changes.”  This conclusion brings to obvious light one of the reasons why cougars survived throughout much of North America where jaguars didn’t.  After Indians overhunted much of North America’s megafauna, jaguars had difficulty finding the larger prey they preferred.  The extinction of two Pleistocene species of peccary in North America was probably devastating.  Indians even overhunted white tail deer into scarcity as John Lawson, an early European explorer (circa 1704) noted when he pointed out that deer were rare around large Indian settlements in South Carolina.  But cougars could survive in these areas on rabbits, possums, raccoons, and turkeys.

I agree that the preference for larger game that no longer exists is one factor that’s limited the jaguar’s range in North America, but I think there are other factors.

Evolution of size, coat color, adaptability to cold, and personality traits

The fossil record suggest jaguars, along with dire wolves, were the most common large carnivores (excluding omnivorous bears) in southeastern North America during the Pleistocene.  Yet, cougars found their niche here too.  During the Pleistocene both species were somewhat larger than the present day versions of these species.  Rancho La Brean specimens of cougars show that on average they were 5% larger than those of today, while Pleistocene jaguars approached modern day tigers in size.  I think this is due to the larger size and quality of prey available, particularly horses and the larger sized species of peccaries, and it’s clear these two big cats not only had a better diet, but further impetus to evolve to a greater size, so they could successfully exploit this larger prey.  One study reported that modern jaguars living in areas where cattle were introduced tend to approach the size of the larger Pleistocene jaguars, and it’s believed that jaguar populations increased following the introduction of European livestock to South America.

I theorize the spotted coat of the jaguar is another factor in its range reduction.  Indians valued the beauty of its fur and hunted them unmercifully.  There’s a possibility that Pleistocene cougars had spotted coats.  Scientists believe that cougars evolved from a kind of spotted cheetah.  Cougar kittens retain these cheetah-like spots–evidence of this evolution.  But I think many adult cougars may have been spotted until very late in the Pleistocene when man colonized the continent and hunted the spotted cougars for their coats, leaving only the dull tawny and gray coated individuals to breed, which in turn genetically swamped the spotted ones.

It has been suggested that spotted cats are more vulnerable to cold climate–another factor which may limit the jaguar’s range, but I disagree with this hypothesis.  The snow leopard of the Himalayas is an example of a spotted cat that lives in a cold region.  Moreover, jaguar fossils have been excavated from as far north as Oregon and Pennsylvania when even during the warmest interglacials, subfreezing temperatures occurred during winter. 

Jaguar fossils in Georgia have been excavated from Ladds Quarry and Kingston Saltpeter Cave.  A nearly complete skull was recovered from the former location along with giant tortoise and armadillo bones that have jaguar gnaw marks on them.  Fossils from this period probably date to a warm climate phase, but the jaguar remains from KSC are associated with the kinds of animals that live in cold and temperate climates, indicating jaguars survived colder conditions than any endured by extant populations.  Cougar fossils also were found at Ladds and in Yarbrough Cave which dates to the last glacial maximum.

One more factor in the cougar’s survival where jaguars didn’t may be evolutionary selection towards more timid individuals.  Those members of the cougar population that learned to avoid man were more likely to survive.  Timidity possibly occurred less frequently in prehistoric jaguar populations.

Cougars vs. Jaguars, wolves, and bears

So which would win in a battle between a jaguar and a cougar?  According to scientific studies, cougar and jaguar ranges frequently overlap, but they tend to avoid each other.  Certainly, a jaguar wouldn’t think it worth the effort to battle a raging mother cougar defending her kittens.  Conversely, a cougar would be out of its mind to engage in a battle with a larger, more powerful cat that bites harder than any other kind of cat in the world.  However, in one paper, international big cat expert, Howard Quigley, did cite a case of a jaguar attacking and killing a cougar.

Packs of wolves also dominate cougars in the Rocky Mountains.  Wolves occasionally kill cougar kittens, sub-adults, and even adults.  The average biomass of wolves in packs that attack a cougar outweighs the cat by a 13:1 ratio.  Rarely, cougars have been reported to kill wolves (sub-adults and adults, but not pups), but in these cases it was one-on-one and the biomass was a 1:1 ratio.  A certain percentage of cougar kills are lost to wolves and bears in areas where their ranges overlap.

References

Carvolcanti, Sandra; and Eric Gese

“Kill rates and predation patterns of jaguars (Panthera onca) in the southern pantanal of Brazil”

Journal of Mammalogy 91 (3) 722-736 2010

Hoogesteyn, Rafael; and Edgardo Mondolfi

“Body mass and skull measurements in four jaguar populations and observations on their prey base”

Bulletin of the Florida Museum of Natural History V. 39 (6) pg. 195-219 1996

Hornocker, Maurice; Sharon Negri, and Alan Rabinowitz

Cougar: Ecology and Conservation

University of Chicago Press 2002

Nunez, Rodrigo; Brian Miller, and Fred Ludjey

“Food habits of jaguars and cougars in Jalisco, Mexico”

Journal of Zoology 252 (3) 373-379

Scognamillo, Daniel; et. al.

“Co-existence of jaguar (Panthera onca) and puma (Puma concolor) in a mosaic landscape in the Venezualan llanos”

J. Zoological Society of London 259 269-277 2003