Posts Tagged ‘Ice Age’

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

November 26, 2012

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.  

Full-size image (83 K)

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)

The Eerie Call of the Common Loon (Gavia immer immer)

January 29, 2012

The call of the loon sounds ghostly.  I imagine the howling of dire wolves and the eerie calling of loons made living in the Pleistocene kind of spooky.  Loons are in the order Gaviformes which is always the first order listed in books about North American birds, meaning they are considered the most primitive avian group living on the continent. Of all the North American birds they must be the closest living relatives of the dinosaurs.  Perhaps some species of dinosaurs had a smilar vocalization.  Below is a link to a youtube video from the Cornell University ornithology department that includes eerie cries of loons.

http://www.youtube.com/watch?v=4ENNzjy8QjU

Common loon.

Loons dive under water and catch small fish–their primary prey, though they also feed upon aquatic invertebrates, insects, and some water plants.  They can take large fish as well, but need to drag them to shore and mangle them before dining.  Loons like to nest on uninhabited islands in lakes, explaining why they migrate north during spring to places like Minnesota where there are lots of lakes.  I always thought of loons as a strictly northern bird, but a few years ago a checklist and count of waterfowl on Clark Hill Lake included a few dozen common loons.  I didn’t know they spent winters in wetlands across the south and have never seen one.  They’ve been reported from many counties in Georgia but are most numerous near the coast where small fish are always plentiful.

Counties in Georgia where common loons have been sighted.  The map should include Lincoln County where they’ve been seen on Clark Hill Lake. The common loon winters in Georgia but doesn’t nest here.  Its present day nesting grounds were under glacial ice during much of the last Ice Age.  Did it nest in Georgia then?

During the Ice Age the present day nesting range of the common loon was under glacial ice.  They must have nested farther south then.  The region between the southern lobe of the Laurentide glacier and the Ohio River may have had numerous small lakes created by meltwater pulses which flooded low lying areas.  Perhaps this is where they mostly nested then.  It’s possible they nested and lived year round in the southeast during the Ice Age.  The overall population probably increased as the glacier receded and opened up more favorable habitat in the north, and they eventually abandoned their southern breeding grounds, though they still return to take advantage of ice free feeding opportunities during winter.

Attached Image: Carpometacarpus, Com. Loon.jpg

A loon fossil (looks like an intact wing) found in Florida by a member of the Fossil Forum.  This is a nice specimen. Did they breed and nest in Florida then or was it just spending the winter?

Three other species of loons spend winters in Georgia.  The red-throated loon (Gavia stellata) has been reported from 19 counties; the Pacific loon (Gavia pacifica) has been reported from 4 counties; and the yellow-billed loon (Gavia adamsii) is a rare accidental reported from only 1 county.