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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The Nature of Paleolithic Art by R. Dale Guthrie

I recently finished reading The Nature of Paleolithic Art by R. Dale Guthrie.  Dr. Guthrie also authored Frozen Fauna of the Mammoth Steppe and dozens, perhaps hundreds, of articles for scientific journals, many of which I’ve read.  It took me almost a month to read The Nature of Paleolithic Art because it’s 500 pages and has small print and numerous pictures on every page that are worth careful examination.  The book is a brilliant creation, taking decades of research and writing to complete.  It’s well-written and the line drawings replicating the cave paintings show Dr. Guthrie is a talented and patient artist.  Because I can’t live in the Pleistocene as I so often fantasize on this blog, I wanted to get inside the heads of the humans who actually did.  Dr. Guthrie does this with his detailed analysis of their art.  Most books about paleolithic art have been written by art historians, anthropologists, and archaeologists, but this book is the first written from the point of view of a vertebrate paleontologist, making it unique.  I noticed amazon.com didn’t have much information about this book, so I will remedy this with a chapter-by-chapter review.

The first chapter is entitled “Drawn from Life.”  It consists of a discussion of how this work compares to others on the subject.  This is where Dr. Guthrie introduces one of the important themes of his book: Most paleolithic art was drawn realistically and the images were not representations symbolizing magic or religion, a view held by many anthropologists.  I agree with Dr. Guthrie.  To me this seems rather obvious–too many scholars look for something deep and complex when there is a much simpler explanation.  The people living in Europe then depended on hunting and that is what they depicted.  This chapter also covers the ecology of Pleistocene Europe.  Humans lived on the ecotone between southern European forests and the vast mammoth steppe that stretched from the British Isles to Alaska.  And there are detailed descriptions of cave geology, preservation, and taphonomy.

The second chapter is “Paleolithic Artists as Naturalists” which was perhaps one of the most interesting for me (well…that and the sex chapter).  He finds usable information about extinct species and extirpated subspecies from cave paintings.

Page from The Nature of Paleolithic Art.  The top drawings depict the most common large mammals living in Eurasia during the Pleistocene including Woolly mammoths, woolly rhinos, Megaloceros–a giant extinct deer, elk, caribou, aurochs–wild cattle, bison, musk-oxen,  horses, asses, ibex, sable antelope, cave bear, brown bear, lions, hyenas, wolves, and humans.

For example the cave paintings inform us that European lions had no manes, and horses in southwestern Europe had some striping, an adaptation for living in brushy habitat.  Dr. Guthrie shows the reader how the cave paintings represent real animal behavior–there are depictions of mating and flight response.

Chapter 3 is “Tracking down the Pleistocene Artists.”  Dr. Guthrie conducted a study that analyzed the hand prints on the cave walls.  Statistical differences between age and sex exist in the measurements of finger and palm size.  The cave painters made the hand prints by spitting a mouthful of red ocher over their hands.  Based on hand measurements, Dr. Guthrie determined most but not all the cave painters were boys aged 12 and under.

A statistical analysis of hand measurements suggests most the cave painters were boys aged 12 and under.  The kids making the hand prints were likely the same kids who were drawing the animals.

Although many cave paintings are masterpieces, most look like something a third grader might doodle.  The highest quality paintings are famous, but they’re vastly outnumbered by little known drawings that were done by less talented or less experienced artists.

It’s no coincidence that nearly every cave with paleolithic art was discovered by teenaged boys.  During the paleolithic just like in the present time, adventurous boys would be the most likely members of society to venture into caves.  Because life expectency was so low then, children made up a bigger percentage of the population then than they do now and teenaged boys would have been a significant segment of society.  Contrary to popular belief, paleolithic people didn’t live in caves but inhabited open air sites, temporary huts, and rock shelters.  This explains why most of the cave artists were young boys.

Chapter 4 is “Testosterone Events and Paleolithic Imagery.”  This one is about the evolution of human behavior and art.  He explains the evolutionary reason why paleolithic men and women differed in the partition of labor and why modern politically correct attitudes stifled early studies on the role evolution played in making men the hunters while women were better able to perform tedious tasks such as sewing clothes.  Younger men with higher levels of testosterone than women took more risks when hunting and were also more likely to explore caves.  Accordingly, the art on caves is more representative of a young male’s point of view.  Much information about women’s contributions is missing–the clothes they made are organic and long gone.  Boys painting on cave walls rarely drew people wearing clothes, even though they must have, considering the harsh climate.  There are rare exceptions.  The few pictures depicting clothes show paleolithic people wearing parkas, hoods, and boots.

Chapter 5 is “The art of Hunting Large Mammals.”  Dr. Guthrie begins by reviewing the evolution of hunting behavior in hominids.  He uses evidence from physiology, sociobiology, ecology, and accounts from the ethnographic record to show that hunting was a driving force in human evolution.  He believes hunting created the modern social bond between man, wife, and child.

Incidentally, Dr. Guthrie believes the red spots on some cave paintings of Pleistocene horses represent the tracking of blood from wounded animals.  This is an alternative explanation for the ones I gave in a previous blog entry– https://markgelbart.wordpress.com/2011/12/02/pleistocene-spotted-horses/

Another page from the book.  These are line drawings of cave paintings.

The chapter on hunting is a long one covering paleolithic weapons, the use of disguises, tracking wounded game, and harpooning fish.

Chapter 6 is “Full-figured Women in Ivory and Life.”  He explains the common depiction of full-figured fat women represents the female sex when they were most fertile. In most hunter-gatherer societies, women are rarely fertile due to a combination of environmental stress and the care of an already existing baby or toddler.  Women were most likely fertile during times of plenty when they had no young children nursing.  Men evolved to identify when women were most fertile.  And, of course, young boys drew pictures on cave walls and sculpted the famous figurines because women with big boobs and big butts were what was constantly on their minds, along with hunting large mammals.

Dr. Guthrie doesn’t go so far as to suggest the possiblity that the Venus of Willendorf represents sex slavery as I did in a previous blog entry– https://markgelbart.wordpress.com/2011/10/14/the-venus-of-willendorf-pleistocene-sex-object/

But he does dismiss the notions they represent fertility or goddess cults.

I don’t agree with Dr. Guthrie when he writes that paleolithic people chose their mates carefully.  The population was so low then that people probably had a hard time even meeting members of the opposite sex who were not related to them, and they had to accept what they could get.

Paleolithic people had many sexual items and enjoyed practices we consider modern.  Cave paintings prove paleolithic women wore lingerie.  Many cave paintings depict buxom women wearing nothing but bracelets, belts, and boots.  Paleolithic dildoes (made of stone) are very common.  One broken sculpture suggests they played bondage games.

Chapter 7 is “The Evolution of Art Behavior in the Paleolithic.”  Here, he discusses the evolution of play and how art is an extension of play.  Art contributed to the survival of paleolithic people because it helped make their brains more creative which did have practical uses.  Creativeness is heritable.

Chapter 8 is “Bands to Tribes.”  Very little paleolithic art is abstract, but the development of agriculture led to an increase in the use of abstract symbols in art.  Humans needed to invent abstract symbols to account for stored foodstuffs.  Agricultural civilization changed the human experience but not all for the better–humans suffered more malnutrition from starch-based diets, they contracted diseases spread from domesticated animals, and they experienced more warfare from being in economically unequal societies.  Not a single paleolithic drawing known depicts a shield or warfare, though individual man on man violence was rarely drawn.

Chapter 9 is “Throwing the Bones.”  This was the only chapter I found uninteresting.  It’s about the evolution of the belief in the supernatural.  There’s not enough concrete evidence left about early human’s supernatural beliefs, making this part of the book too vague and unnecessarily long-winded.  That’s really the only negative criticism I have of the book.  Sometimes, Dr. Guthrie overwrites and gives 5 or 6 examples when 1 0r 2 would have been enough.  Otherwide, I enjoyed the book very much.

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

The South Central Salient of the Helmeted Musk-ox (Ovibos cavifrons or Bootherium bombifrons)

Portrait of the woodland or helmeted musk ox from the Illinois Museum of Natural History

The way scientists assign scientific names to extant and extinct species can be confusing.  The rule is simple–the scientific name given by the scientist who first describes the first specimen ever discovered (also known as the “type specimen”) is the one that supercedes all other later names.  Complications arise when other scientists discover new fossil material of the same species and mistakenly believe they’ve discovered a new species, and they assign a completely different scientific name to the specimen.  Decades often pass before other scientists compare the fossils and determine they’re one and the same species.  The extinct helmeted musk-ox provides a case study of this confusion.  Scientists discovering fossils of this wide-ranging species from all over the continent have assigned many different scientific names to this species including Bos bombifrons, Bootherium bombifrons, Symbos cavifrons, Ovibos cavifrons, Bison appalachicolus, Liops zuniensis, Symbos australis, Bootherium nivicolum,  Symbos converifrons, Ovibos giganteus, and Bootherium brazosis.  This sounds like a joke, but it’s not.  It created a real mess for later scientists to straighten out.

Fossil hunters first found a helmeted musk-ox fossil in 1804 at the Big Bone Lick Fossil site in Kentucky.  The first scientist to look at it put it in the Bos genus which is the same one domesticated cattle belong to.  It wasn’t until 50 years later that it was recognized as a type of musk-ox.  Extreme sexual dimorphism caused the proliferation of species names for just one animal.

The horns on a male helmeted musk-ox were much larger and robust than those on the female.  Scientists mistakenly thought they were from two different species.  Note the difference between the male and the female horns (f & e) in this diagram.  Diagram from the below referenced paper written by R. Dale Guthrie.

Male helmeted musk-oxen are so much larger than females that for a long time scientists believed they were seeing different species: males were classified as Symbos cavifrons, and females were classified as Bootherium bombifrons.  Finally, in a paper written in 1989 Jerry McDonald and Clayton Ray thoroughly studied all the fossil material and determined they were one and the same species.  Because Bootherium bombifrons was the older name, that is now considered the official scientific name for the species.  I mistakenly thought Ovibos cavifrons was the official name, and it makes sense because its close living relative, the woolly musk-ox goes by the scientific name of Ovibos moschatus. It seems the woolly and helmeted musk-ox should be in the same genus, but they’re not.

I’ve noticed a curious geographical distribution of helmeted musk-ox fossils.

Distribution map for helmeted musk-ox.  This map includes just the skulls, so I added a dot for a musk-ox fossil found in Nashville, Tennessee, and drew the line to illustrate the salient.  Helmeted musk-ox must have been an adaptable animal to range this far.  Map from the below referenced paper written by McDonald and Ray.

Helmeted musk-oxen fossils come from Bayou Sara in south central Louisiana, Texas, and Mississippi north to Alaska and west to northern California and east to the continental shelf off what today is New Jersey.   Their range seem to have extended south along the Mississippi River.  A south central salient of its range is notable.  Fossil sites in the piedmont region of the southeast are so rare there is no telling where its southeasternmost range occurred.  None have been found in Florida’s abundant sites, indicating its probable absence there.  Fossil sites in Nashville, Tennessee and Saltville, Virginia yield helmeted musk-oxen specimens, but it may have been absent from the southeastern coastal plain.  Looking at the line I drew on the above map, it’s likely helmeted musk-oxen did range over northern Alabama and the ridge and valley region of northwestern Georgia. 

If they could survive the warmer climates of Mississippi, Louisiana, and Texas, it couldn’t have been climate that prevented them from colonizing the southeastern coastal plain.  Perhaps, because long-horned bision were already abundant here and occupied a similar niche, helmeted musk-oxen never could become established.  Maybe, it’s just chance they never migrated into the region.  Or maybe they were present but in such low numbers as to be invisible in the fossil record. 

The extinct helmeted musk-ox differed from the living woolly musk-ox in many characteristics.  As evident from its much wider range, the helmeted musk-ox was much more adapatable.  It had longer legs allowing it to run greater distances and with more speed.  It was taller and more slender, suggesting it had more endurance.  Scientists found fur on one specimen.  The hair was shorter and finer–evidence that it did not have a heavy woolen coat like its living cousin.  The two species did coexist in parts of Alaska and unglaciated Canada, but Dr. Guthrie sees evidence of habitat parturation.  Helmeted musk-oxen lived in arid grassy steppes in this region whereas woolly musk-oxen inhabited more mesic tundra.  Dr. Guthrie favors the common name helmeted musk-ox over woodland musk-ox because the species was just as likely to be found on grassy steppes and savannahs as open parkland woods.  I agree with him and from now on will refer to it on this blog as the helmeted musk-ox.

Evidence from fossilized feces and plant fragments in fossil teeth show that helmeted musk-oxen ate a wide variety of plant foods including sedges, grasses, blueberry bushes, and willow twigs.  In fact one sample of fossilized dung consisted of nothing but willow twigs.  Some times their feces was pelletized.  Dr. Guthrie states that this is evidence of a capability to eat a lot of dried plant foods without having to eat snow for water.  It’s an adaptation of moisture conservation, enabling the species to survive frigid arid environments. 

Helmeted musk-oxen were able to live in temperate climates where human populations eventually became high.  I believe this is the reason they became extinct while woolly musk-oxen avoided human overhunting in remote regions of the arctic.  It’s ironic that an animal that was more adapatable died out because of this adaptability.  I disagree with scientists who think natural environmental changes caused their extinction.  This highly adaptable animal enjoyed a wide range during the Pleistocene as the above map shows.  This means they inhabited a great variety of habitats from Alaskan grassy steppe to prairies to open forests interspersed with meadows.  Suitable environments  for helmeted musk-oxen, especially in the midwest and upper south, never completely disappeared.  The foods they ate–grasses, sedges, blueberry bushes, willow trees–always remained abundant throughout much of the continent.  Moreover, their fossils are known from deposits as old as 300,000 years BP, meaning they survived previous transitions from glacial to interglacial.  I see no change in the environment that would cause their extinction, other than the increase in the number of people hunting them.  Dr. Guthrie suggest bison outcompeted musk-oxen on the prairies, but this makes little sense–musk-oxen and bison coexisted for hundreds of thousands of years.

Woolly musk-oxen survived extinction because they inhabit remote regions of the arctic.  Even here, human hunting reduced their numbers.  Human hunters wiped out woolly musk-oxen  in Alaska before the introduction of firearms, though the beasts have been reintroduced here.  Still, there are large areas of suitable habitat in Alaska where woolly musk-oxen are absent due to human hunting.   During the Ice Age woolly musk-oxen were more widespread living as far south as Spain.  Undoubtedly, climate change and the resulting contraction of barren tundra has played a role in diminishing habitat for this species, but suitable habitat for helmeted musk-oxen expanded following the retreat of the glaciers, especially in the midwest.  Suitable habitat in the upper south remained the same. 

I hypothesize men exploited the musk-ox’s habit of standing in a defensive circle to face down predators.  It may prove effective against wolves or big cats as long as they don’t panic and begin running (as seen in this video http://www.youtube.com/watch?v=pb6Rke7jiTc ) but it was catastrophically fatal for helmeted musk-oxen when a gang of humans confronted them.  Humans could use projectile weapons to slaughter entire herds standing stationary in one place.

Some scientists claim the scant evidence that humans hunted helmeted musk-oxen suggests they played no role in their demise.  This argument frustrates me.  There isn’t a single skeleton of a human from the Clovis era in North America.  Why should we expect to find remains of their meals?  Nevertheless, there is some evidence of humans exploiting helmeted musk-oxen.  Clovis age arrowheads associated with musk-oxen bones and with bovine blood on them were found at the St. Mary’s reservoir in Alberta, Canada.  And a human “modified” musk-oxen bone turned up at the fossil site in Saltville, Virginia (a pre-clovis site).  Scientists who argue against the human overkill model of extinction never say how much evidence would be enough to convince them.

References:

Guthrie, R. Dale

“New Paleoecological and Paleoethological Information on the Extinct Helmeted Musk-oxen from Alaska”

Ann. Zool. Fenninci 28: 175-186 Feb. 1992

McDonald, Jerry; and Clayton Ray

“The Autochthonous North American Musk-Oxen Bootherium, Symbos, Gidleyea (Mammalia: Artiodactyl: Bovidae)”

Smithsonian Contributions to Paleobiology #66 1989