The Beringian Buckle Stopped Rhinos from Recolonizing North America During the Pleistocene

Many magnificent mammals roamed the Americas during the Pleistocene but one of the most spectacular was conspicuously absent.  The abscence of rhinos from Pleistocene America was for a long time an ecological mystery.  The Bering Landbridge has intermittently served as a gateway between Eurasian and American fauna.  Bison, mammoths, elk, saiga antelope, brown bears, and lions crossed from Siberia to Alaska while horses and camels crossed from Alaska to Siberia.  The Bering Landbridge emerges above sea level during Ice Ages transforming the Bering Straight from ocean to habitable land where this faunal interchange can take place.  

Map of the Bering Landbridge.  Note how vast it was.  It comprised tens of thousands of square miles. The southern half was good quality wildlife habitat but some species of animals, such as rhinos, could not survive on it, explaining why a certain proportion of animal species were filtered out of the transcontinental faunal exchange.

Recently, some paleoecological studies of areas in Alaska and Siberia that are immediately adjacent to the Bering Straight yielded evidence explaining why some animals, such as the woolly rhino (Coleodonta antiquatatas), never crossed the Bering Landbridge.  The northern half of the landbridge was likely blocked by glaciers.  The southern half consisted of moist shrubby maritime habitat drastically differing from the vast grassy steppes that existed on both sides of the Landbridge.  R. Dale Guthrie calls this habitat a “buckle in the belt of mammoth steppe,” a biome that existed from Europe across Asia and continued again in most of Alaska with the exception of the coastal regions.  The Beringian Buckle provided a barrier for some mammals, stopping woolly rhinos from colonizing America but also preventing such American species as ground sloths, short-faced bears, American donkeys, late Pleistocene camels, bonnet-horned musk-oxen, and badgers from colonizing Eurasia.  The studies also found different species of steppe-grass adapted beetles on each side of the buckle.

A riparian willow habitat in the Rocky Mountains.  This might have been similar to the kind of habitat in Beringia that woolly rhinos and certain kinds of grass-dependent beetles couldn’t survive in long enough to traverse, but woolly mammoth, bison, horses, and elk could.  On the east and west sides of the Beringian Buckle were vast steppe grasslands suitable for woolly rhinos.  However, they never could get to the east side.

Artist’s rendition of the Woolly rhino.  Note the size of its horn.

Climatic conditions over the interior regions of the continents during the Ice Ages created clearer skies and drier conditions than occur presently in Siberia and Alaska.  Temperatures were even colder than they are today, but there was less precipitation and cloud cover, creating an environment of grass interspersed with sand dunes.  The greater amount of sunlight thawed the permafrost.  Unlike today’s Alaska and Siberia, there were no spruce forests or any trees at all.  But the Beringian Buckle experienced more cloud cover and precipitation due to the region’s vicinity to the ocean.  The greater amount of precipitation and cloud cover allowed a shrubby maritime habitat to flourish, and it was quite different from the grassy steppe that covered so much of the northern hemisphere.  The Beringian Buckle served as a refuge for wet tundra plants that later recolonized Alaska and Siberia and unlike the interior of the continents then, it was studded with lakes.

Woolly rhinos weighed on average 7000 pounds, making them the 2nd largest Ice Age mammal in Eurasia.  They originally evolved 3.7 million years ago on the grassy Tibetan Plateau, long before Ice Ages began to occur.  When Ice Ages began to occur on a cyclical basis, woolly rhinos were able to expand their range across most of Eurasia.  Some scientists have tied their extinction to the end of the Ice Age when the Mammoth Steppe habitat contracted.  However, I disagree with this assessment because they originally evolved before Ice Ages began to occur, and they survived previous interglacial conditions.  I do agree that their range contracted following the end of the last Ice Age but some steppe habitat remained as happened in previous interglacials. (Areas of Mongolia where wild and domestic horses and nomadic herders still thrive is an example of suitable steppe habitat capable of supporting woolly rhinos.)  I propose the population of woolly rhinos living on relic steppe habitat after the end of the Ice Age were wiped out by men.  If not for men, I believe woolly rhinos would still exist, ready to expand their range again upon commencement of the next Ice Age.

I hypothesize a similar scenario for 2 other Eurasian species of Pleistocene rhinos.

Merck’s rhino (Stephanorhinus kirchenbergensis).  The background setting of the illustration is inaccurate.  This species preferred temperate forest habitats.

The narrow nosed rhino (S. hemitoechus) also lived in temperate regions of Eurasia but preferred meadows and prairies.

Merck’s rhino lived in temperate forests from what’s now England east to Korea and from Germany and Poland south to Israel.  It was adapted to eat forest vegetation.  The narrow-nosed rhino lived over much of the same geographic range but was adapted to open grassland habitats, eating mostly grass.  Both evolved from and replaced a common ancestor (S. hudsheimensis) that was adapted to eat both forest and grassland vegetation.  The extinction of both species coincides with the beginning of the Last Glacial Maximum when forest and meadow were replaced by the arid Mammoth Steppe habitat.  Relic habitat suitable for both temperate species of rhinos may have remained in southern Europe but relic populations of rhinos then were more vulnerable to human hunters.  If not for man, I believe both of these species would have survived on these relic habitats and recolonized Europe following the end of the Ice Age.

Climate change did cause the complete extinction of rhinos in North America before the Pleistocene began.  North America was home to several species of rhinos during the Miocene.  The hippo-like rhino (Teloeceras major) and the hornless rhino (Aphelops) were the most common large herbivores in America other than horses for about 20 million years.  Their extinction coincides with the first Ice Ages that occurred at the beginning of the Pliocene ~5 million years ago.  They may have been incapable of surviving frosts or changes in vegetation.  So it is possible that Pleistocene Eurasian rhinos succumbed to changing climate, but man is a strong suspect in my opinion.

References:

Elias, Scott; and Barnaby Crocker

“The Bering Landbridge: a moisture barrier to the dispersal of steppe tundra biota”

Quaternary Science Review 27 (December 2008)

Guthrie, R. Dale

“Origin and Causes of the Mammoth Steppe, a story of cloud cover, woolly mammal tooth pits, buckles, and inside-out Beringia”

Quaternary Science Review 20 (2001)

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Pleistocene Fossil Canid Ratios Recorded in the University of Florida Database

The abundance of Pleistocene fossil sites in Florida has allowed the university in Gainesville to become a center of information for other scientists.  Scientists excavating new fossil sites use existing fossils at the University of Florida Museum of Natural History to help identify the new specimens they pull from the earth.  It’s not always easy to differentiate closely related species–the subject of this blog entry, the canids, are notoriously difficult to distinguish.  Vertebrate zoologists and paleontologists measure and describe every part of every bone and tooth when examining new specimens.  They publish this information in scientific journals and accumulate knowledge of the size limits and shape variations of a particular species’ anatomy.  If a newly discovered fossil tooth for example doesn’t fit any known pattern of shape or size, than scientists suspect they may have discovered a new species.  The more data scientists have, the better able they are to identify new species and spot evolutionary trends over time within a species.

Fossil collecting is popular in Florida, thanks to all the sinkhole lakes and caves with basal chemistry in the soil that preserves bones.  Amateur fossil collectors have many more fossils in their collections than the University of Florida’s Natural History Museum..  Many are for sale as well.  It would be a great benefit to science, if collectors made arrangements to donate their collections to the museum upon their deaths.  Many valuable specimens have been lost when their owners die and family members, not interested in the subject, lose track of where they put the old bones.

My little study is limited to canid fossils listed on the University of Florida database and leaves out the great many more in the hands of amateur fossil collectors.  I also limited this survey to the Rancholabrean Land Mammal Age (300,000 BP-11,000 BP), leaving out Armbruster’s wolf which dominated the middle Pleistocene before being replaced by dire wolves.  Nevertheless, I think there’s enough information to suggest relative canid species abundance during the late Pleistocene.  Keep in mind, I was counting on a computer screen while scrolling down, so my numbers may be off slightly.

Listed on the Florida Museum of Natural History’s database, I counted 64 dire wolf (Canis dirus) specimens, 34 coyote (Canis latrans) specimens, 1 red wolf (Canis niger) specimen, 9 domestic dog (Canis familiaris) specimens, 0 dhole (Cuon alpinus) specimens, and 55 gray fox (Urocyon cineorgenteus) specimens.

The fossil record strongly suggests that from 300,000 BP to about 11,000 BP dire wolves were by far the most common large canid being about twice as abundant as coyotes.  Red wolves were rare but present.  Gray foxes were just as common during the Pleistocene as they are today.  These neat little foxes have the ability to climb trees, a skill that saves them from their larger relatives.  There is no evidence of dholes but as I wrote in a previous blog entry http://markgelbart.wordpress.com/2011/06/01/did-the-dhole-cuon-alpinus-range-into-southeastern-north-america-during-the-pleistocene/ , I suspect they may have periodically colonized parts of the southeast but in numbers too low to leave fossil evidence.

Dire wolves were the dominant large canid in the southeast (and all across North America south of the Ice Sheets) during the late Pleistocene.

Coyotes probably occupied a niche similar to African jackals.

Gray foxes thrived in areas where they had access to trees and could escape larger predators.

The presence of domesticated dogs in the Pleistocene fossil record puzzled and surprised me.  I almost didn’t even do a database search for Canis familiaris and only did so as an afterthought.  Most anthropologists don’t think humans domesticated dogs until after the Pleistocene about 10,000 years ago, but the fossil evidence contradicts this.  In fact scientists recently discovered the skull of a domesticated dog in a Siberian cave that dates to 33,000 BP.  They determined  this particular domesticated dog was not the ancestor of the lineage that led to today’s dogs but instead its descendents died out.  It’s probable that there were many early lineages of domesticated dogs that ceased to exist for various reasons.  Perhaps that group of people died out or stopped keeping dogs.  The popular idea that people domesticated dogs by kidnapping and raising wolf pups is a misconception.  Scientists think it’s the other way around–dogs adopted us.  Dogs are descended from the wolves which had the least flight response.  Wolves that hung closely around human campsites for access to leftovers gave birth to pups with floppy ears, multi-colored coats, and other dog traits that differentiate them from other wolves.  The gene for tameness shares a pathway with the gene for these physical characteristics.  So it’s likely that dogs adopted people in many different geographic locations wherever wolves (Canis lupus) began occupying areas adjacent to human campsites.  Obviously, dogs either followed or were brought to Florida by the Paleo-Indians.

The authors of a chapter in the book The First Floridians and the Last Mastodons suggest that all the coyote fossils found in Florida are actually domesticated dog fossils, but they only knew of a handful of coyote fossils.  Apparently, they didn’t know 34 specimens had been found.  I doubt scientists made that many misidentifications.

Dire wolves succeeded in becoming one of the dominant predators in the environments of southeastern North America where they found a wealth of prey roaming the open woodlands and savannahs.  Everything from bison and horses to deer and rabbits sustained them, and a mammoth or mastodon that died of natural causes provided a feast.  Coyotes successfully co-existed with dire wolves by scavenging large predator kills and by hunting rodents.  Red wolves must have been restricted to islands and perhaps deeply wooded swamps where they could survive on deer and small game.  Their niche must have been areas with lower densities of prey as opposed to grasslands that hosted large herds of ungulates.  Following the extinction of the megafauna and dire wolves, forests replaced grasslands and red wolves increased in number and drove coyotes completely out of the south.  But after European settlers wiped out the red wolves, coyotes returned.

References:

Ovodov, Nikolai, et. al.

“A 33,000 Year Old Incipient Dog from the Altai Mountains of Siberia: Evidence of the Earliest Domestication Disrupted by the Last Glacial Maximum”

Plos One 6 (7) 2011

http://www.flmnh.ufl.edu/databases/vp/intro.htm

The Dunwoody Nature Center

I attended my nephew’s bar mitzvah in Dunwoody, Georgia last weekend.  Dunwoody consists of dozens of subdivisions and plenty of shopping centers and absolutely no rural farmland.  I didn’t hold out much hope for a nice nature walk here–the traffic is terrible.  But at least the developers left a lot of trees standing.  I decided to walk from my sister’s house to a little park known as the Dunwoody Nature Center and I discovered a surprising gem.

This white oak was about 4 feet in diameter.  White oak is a common tree in Dunwoody.

From the composition of the trees left standing most of Dunwoody must have once hosted a pretty nice dry upland forest.  Too bad developers converted it into a crowded suburb.  Today, white oaks, black oaks, southern red oaks, shortleaf pines, and loblolly pines are the dominant trees.  The Dunwoody Nature Center slopes sharply down toward Wildcat Creek, the name of which is a relic to its former status as a wilderness.  The woods here are dominated by beech, white oak, sweetgum, river birch, and loblolly pine.  I was stunned to see a woodlot of mostly beech trees in central Georgia.

A mature beech tree growing on the edge of a rocky creek.  It’s surrounded by many immature beech saplings.

Fossil pollen studies show beech was a common tree in the south during the end of the Ice Age when the Laurentide glacier began melting and releasing more moisture in the atmosphere creating a climate that was still cool but more rainy than it was during the height of the Ice Age.  The presence of abundant beech in the fossil record is indirect evidence of massive flocks of passenger pigeons.  Passenger pigeons fed on acorns–in some places completely eliminating the oak seed crop…and the beech’s competition.  Although beech trees produce an edible nut, they can also spread from roots and could survive their seed being consumed by passenger pigeon flocks.  Since the passenger pigeon’s demise, oak forests have been replacing beech forests in many areas.  So I was delighted to see this remnant beech forest in central Georgia.

Wildcat Creek flows through a granite outcropping.  Here is a miniature waterfall.

Two little league baseball fields take up about half the space of the park.  The park is heavily used by dog and toddler walkers.  It’s popularity shows that the planning commission in charge of developing Dunwoody should have arranged for the purchase of more land for more parks.

The Beauty of Pleistocene Swans (Cygnus buccinator)

Photo from google images of a trumpetor swan.

No animal symbolizes the beauty of the Pleistocene more than the trumpetor swan (Cygnus buccinator).  I suppose we can consider it a stroke of good fortune that this species didn’t become extinct with the spectacular megafauna of that bygone era.  Contemporary efforts to protect the bird and help re-expand its range have even been moderately successful.

Modern range map of the trumpetor swan.  It occurred as far south as South Carolina during colonial times.  During the Pleistocene there was likely a sizeable population of this species in the southeast where it is completely absent today.  Fossils of this species have been recovered from northern Alabama and Florida.  Overhunting by men extirpated this species from much of its former range.

Before European settlement of North America trumpetor swans were more common and widespread, migrating as far south as South Carolina during severe winters.  But during the Pleistocene they ranged even further south.  Bell Cave in northern Alabama and several sites in Florida have yielded fossils of this bird.  Ice Ages provided ideal habitat for this species.

Audubon mentions that trumpetor swans prefer a moderate climate.  Ice Age summers in the south were generally cooler and winters were still moderate, so swans would have had a favorable climate in this region then.  It seems likely that Pleistocene trumpetor swans bred and nested on the abundant glacial lakes near the boundaries of the great ice sheets. Then during winter they didn’t have far to migrate because the distance between glacial lakes and favorable wintering habitat in the south was much less than the distances they have to travel today.  Perhaps a segment of the population remained and nested in the south year round, much like modern day sandhill cranes of which some migrate and some are permanent residents.

Map of the Laurentide glacier.   During the LGM swans didn’t have far to migrate between summer nesting grounds near glacial lakes and winter habitat in the south.  Some segments of the population probably lived year round in the south.

Swans inhabit ponds and small lakes with aquatic plants growing on the bottom upon which they feed. Extensive beaver ponds and marshes, and oxbow lakes were the kinds of abundant habitat in the south available to the big birds then.  Swans nest and take cover on beaver dams, muskrat lodges, and islands where they’re relatively safe from mammalian predators. If hungry enough, mammalian carnivores will expend the energy to swim and search for food in wetlands, but it’s not their first choice when looking for an easy meal.  During stadials, islands on braided rivers were common, giving swans lots of favorable habitat.  This wouldn’t have kept swans safe from eagles, however.

Photo from google images of a bald eagle killing a swan.  Eagles of several kinds were common during the Pleistocene.

Grinnell’s crested eagles, golden eagles, and bald eagles were capable of hunting and killing swans during the Pleistocene.  But swan defense mechanisms were adequate enough to maintain substantial populations.  Swans weigh up to 30 pounds and a blow from their wing is powerful enough to break human bone.   They can also flee by submerging and swimming for some distance.  They’re most vulnerable to eagles and human hunters when in flight.

Swans have an interesting method of feeding.  While they swim on the water, they lower their long necks to reach the aquatic plants growing on the bottom.  Because they have longer necks than geese, they can outcompete them for food by eliminating all the fodder within a goose’s reach.  Swans also graze grass on land; and they eat snails, reptiles, and small mammals.

If I Could Live In the Pleistocene (Part Three)–The Turkey Trap

(For parts 1 and 2 of this irregular series, see the September archives.)

I imagine living in my snug adobe brick house on December 10th, 41,000 BP.  Though this is during an interstadial, a warm wet climatic phase occurring within the time span of the Wisconsinian Ice Age, the weather currently is dry and cold; the temperatures are dropping to 10 degrees Fahrenheit at night, and all three of my wood stoves are turning wood I chopped into fire and smoke and indoor warmth.  I’m hungry for meat, but I’m a little tired of eating venison and peccary, and in this cold weather I don’t feel like getting wet checking my fish traps on the river.  This year, no bison came close enough to my home for me to kill and butcher, so I have no beef.  Instead, I’ll settle for turkey.

Turkeys were abundant during the Pleistocene, large flocks of perhaps 100 or more roam the woods around my house in the Pleistocene piedmont region.  I awoke to the sounds of their gobbling this morning.  Fossils of turkeys in Georgia have been recovered from Kingston Saltpeter Cave and Ladds Mountain, both in Bartow County, which is halfway between Atlanta and Tennessee, so that’s the real evidence they were common here.  There were two species of turkey, at least in Florida, during the Pleistocene, including the common one found today Maleagris gallipavo, and Maleagris leopaldo or anza, western species that colonized the southeast during glacial stages when a corridor of grassy scrub habitat extended along the gulf coast on land now submerged by the Gulf of Mexico.  Warm tropical climate allowed even more species of turkey (at least 7) to live across North America during the Pliocene.  Turkeys evolved in America from a peacock-like ancestor, Rhegiminornis calbates, during the Miocene.  Fossils of this ancient species were discovered in Florida.

Habitat in the Pleistocene piedmont of what’s now Georgia was almost ideal for turkey.  Modern day wildlife game managers work with farmers and lumber companies to maintain turkey managment areas that include fields half-covered with small trees and shrubs.  Turkeys forage for weed seeds and insects in the fields but can retreat to brush to escape predators such as great-horned owls and bobcats.  In addition they like fields that border forests of mature trees that provide roosting sites and mast.  Pollen evidence from the Nodoroc site in Winder, Georgia suggests the piedmont region of what’s now Georgia (about 29,000 years BP) was 75% forest and 25% meadow–an environment in which turkeys would thrive.  Fire, drought, rapid climate fluctuations; and megafauna browsing, grazing, and trampling maintained open areas within the forest where turkey populations probably were high most of the time. 

In late fall and early winter male turkeys are in good condition, living in bachelor flocks and fattening on acorns.  So now is the time of year to catch and eat them (Of course, I’m referring to my imaginary Pleistocene existence.  Hunting season for present day turkeys  is in the spring), but I don’t want to aimlessly wander the wilds where in my distraction of the hunt, I might get ambushed by Smilodon fatalis or some other big cat.  Instead, I’m going to use a colonial American method that was formerly quite common and effective–the turkey trap.  There’s a modern misconception that our colonial ancestors were all gun-toting hunters.  Although it’s true that many did have firearms and did actively hunt, most did not.  In fact, gun ownership per capita was lower during colonial times than it is today.  Hardworking farmers didn’t have time nor the strength for hunting after putting in 12 hour days plowing the fields, taking care of the livestock, building fences, chopping firewood, doing household chores (like making soap from scratch and smoking hams), and making carpentry repairs on their cabins.  To catch wild game for the cooking pot, they set traps and snares.  Turkey traps were devastating for the birds.

Sketch of a colonial turkey trap.  The ditch dug under a wooden pen was baited with corn.  The turkeys followed the bait into the pen but couldn’t figure their way out in much the same way a crab trap works.  I have no idea who drew this sketch but I found it at http://woodsrunnersdiary.blogspot.com/

Colonial turkey traps consisted of a small wooden shed and a ditch baited with corn.  The ditch extended under the shed.  The turkey went into the ditch, ate and followed the corn into the shed or pen.  They’d hop up into the shed to eat more corn…but didn’t have the sense to escape by following the ditch back outside.  The colonists could then simply open a hatch to the pen, grab the bird, and execute it.  These traps could yield many birds at once.  According to J. J. Audubon, colonists occasionally forgot to check on the traps, perhaps they were too busy working or they got tired of eating turkey, and dozens of turkeys would starve to death and rot, making the whole area stink.  Audubon also reported that predators occasionally were attracted to these turkey pens–he once discovered a black wolf feeding on trapped turkeys.  In my Pleistocene world I block the entrance to my turkey trap when not in use because I abhor waste.

Reportedly, wild turkeys have better flavor than domestic turkeys, and they have more dark meat but less white.  The chances of catching one much larger than supermarket turkeys are also much higher.  Modern domestic turkeys are bred to have white skin and extra large breasts, and they’re most often harvested when they reach 15 pounds.  Domestic turkey breasts are so large, the meat must be embalmed with a salt water solution to keep the birds from drying out during roasting.  They’re bred to have white skin because it is more visually appealing than the black skin of the wild birds.  They are sold as 15 pound birds because that’s about the right size for roasting.  Wild turkeys that I catch in my Pleistocene turkey trap can weigh as much as 30 pounds.  I don’t bother roasting them.  Instead, I stew the thighs and drumsticks in a crockpot.  I shred the cooked meat and smother it in a gravy made from the liquid they cooked in.  I thicken it with a roux of butter and flour and season it with salt, sage, and thyme.  The shredded meat and liquid makes an excellent base for a Brunswick stew with vegetables grown in my Pleistocene garden (crushed tomatoes, corn, lima beans, potatoes, onions) and seasoned with salt, and red and black pepper.  The dark meat makes good ground meat and mixed with half venison yields an delicious meatloaf.  I smoke the breasts and wings.  The smoked breast meat is good for sandwiches; the smoked wings season a pot of red beans.  The breast meat can also be cut into filets and breaded and fried or cooked in a pan sauce with wine, mushrooms, and garlic.  Turkey carcasses make soup stocks superior to that made from chicken, so I have a ready supply of broth for the kitchen as well.