Archive for the ‘Pleistocene Mammals’ Category

Genetic Study Suggests Fox Squirrels (Sciurus niger) and Gray Squirrels (S. carolinensis) May Interbreed

September 14, 2019

Naturalists have observed male fox squirrels chasing female gray squirrels.  Male Squirrels chase female squirrels during mating season, and if they catch the opposite sex, it demonstrates their fitness for procreation.  Fox squirrels have never been observed actually mating with gray squirrels, and as far as I can determine, nobody has ever reported an hybrid between the 2 species.  However, a new study suggests they may interbreed or have interbred in the past.

Fox squirrel a coat of many colors

Black fox squirrel.

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Melanistic fox squirrel I photographed outside Spring Island, South Carolina.  This was before I had the benefit of a telephoto lens.  Click to enlarge.

It is estimated there could be as many as 25,000 black squirrels in the east of England

Melanistic gray squirrel.

The mutation for having a black coat (melanism) arose twice in fox squirrels from 2 different populations–an example of convergent evolution.  Western fox squirrels have 1 allele associated with melanism, while eastern fox squirrels have a different allele associated with melanism.  (An allele is defined as 1 of 2 or more alternative forms of a gene that arose by mutation and are found on the same place in the chromosome.)  Scientists believe the alleles for melanism in fox squirrels arose for different reasons.  The black coat on western fox squirrels helped them stay warm and more active in a region with colder climate.  The black coat on southern fox squirrels helps camouflage them because it makes them harder for hawks to see in a shady canopy.  The allele for melanism in western fox squirrels is exactly the same as found in melanistic gray squirrels.  Statistical models suggest the most likely explanation is interbreeding between fox and gray squirrels, though they can’t rule out 2 other explanations.

The allele for melanism may have originated in the common evolutionary ancestor of both species.  Alternatively, the allele for melanism may have arisen first in gray squirrels and was passed on to fox squirrels.  But the most likely explanation is it arose in fox squirrels and was passed on to gray squirrels during interbreeding.

Melanistic gray squirrels are more common in the northern region of their range because the darker coat keeps them warmer when they are outside during winter.  The authors of this study believe the black coat helped gray squirrels colonize newly deglaciated territory following the end of the last Ice Age when the climate was still quite cold.  They didn’t estimate how long ago fox squirrels passed on the melanistic mutation to gray squirrels.  It seems likely this may have occurred a long time ago when both species had recently split from their common ancestor.

Gray squirrels were introduced to England and have now almost completely displaced native Eurasian red squirrels ( Sciurus vulgaris).  Melanistic gray squirrels are replacing the original population of gray squirrels that outcompeted red squirrels in England.

It’s easy to tell the difference between gray and fox squirrels.  The latter are generally twice the size of the former.  A juvenile fox squirrel may be about the same size as an adult gray squirrel, but it is still easy to identify the correct species.  Gray squirrels generally have a white belly, while fox squirrels are solid-colored on the torso and belly.  Fox squirrels often have masks; gray squirrels almost never do.

Reference:

McRobie, H.; N. Moncrief, and N. Mundy

“Multiple Origins of Melanism in Two Species of North American Tree Squirrels (Sciurus)”

BMC Evolutionary Biology   2019

 

 

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17,000 Year Old Cougar Crap Found in Argentina

September 7, 2019

When I was researching cougars for my book about 12 years ago and typed the word into a google search, the page was dominated by information about older women who wanted to have sexual relationships with younger men.  This was an unexpected result.  I wanted to learn more about the big cat,  Puma concolor, not about older women seeking younger men.  I see that has changed since then and there are more balanced results with equal representation between the 2 different definitions.

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Female cougar and young.  I hypothesize Pleistocene adult cougars were spotted.

Cougars were a common large predator throughout most of North America from about 500,000 years BP, until European colonization.  They apparently share a common ancestry with an extinct species of pseudo-cheetah known as Miracinonyx inexpectus.  The cougars that lived in North America then were an extinct ecomorph that was replaced from a population of cougars originating in eastern South America after the great Pleistocene megafauna extinction.  Recently, a cougar coprolite (fossilized feces) was found inside a rock shelter in Catamarca, Argentina.  This region is mountainous and dry, explaining why it was so well preserved.  Scientists used DNA to identify the turd came from a cougar.  They also found DNA belonging to Toxascaris leonine, a parasitic roundworm.  This is the oldest parasitic DNA ever recorded.  Scientists previously thought this species of roundworm was brought to North America inside the guts of domesticated dogs and cats, but this coprolite dates to 17,000 years BP before domesticated pets were brought to the New World.  The species of cat ancestral to the cougar likely brought this parasitic roundworm across the Bering Land Bridge millions of years ago.

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Toxascaris leonine.

Cougars often ingest roundworms when they eat rodents.  Ingested eggs hatch in the small intestine, and the worms mate and lay eggs that are then passed in the feces.  Rodents consume the eggs and are in turn eaten by the cats and the lifecycle continues.  Adult worms can reach lengths of 3-7 inches.  This species of roundworm can make cats sick, but not as bad as other species that can cause fatal parasitic infections.  T. cati and T. canis  may travel to an animal’s lungs, causing death.  Most kittens are infested with T. cati  through their mother’s milk.  Most survive and naturally get rid of the parasites.  De-worming medications cure infections too.

Reference:

Petrigh, R.; J. Martries, M. Monding, and M. Fugass

“Ancient Parasitic DNA Reveals Toxascaris leonine Presence in Fossil Pleistocene of North America”

Parasitiology 146 (10) 2019

Saber-tooth Cats (Smilodon fatalis) and Dire Wolves (Canis dirus) Did Not Compete as Much as Previously Thought

August 10, 2019

Image result for Charles Knight classic painting of La Brea tar pits dire wolf

This classic painting of dire wolves contesting a carcass with a saber-tooth may give the wrong impression.  A new study suggests their diets didn’t overlap as much as previously thought.

A new study analyzing the isotopic chemistry of tooth enamel from carnivores excavated from the La Brea Tar Pits determined there was not as much overlap in the diets of saber-toothed cats and dire wolves as previously thought.  An earlier study examined the isotopic chemistry from bone collagen of La Brea carnivores, and the results of that study suggested the big 3 carnivores (saber-tooths, dire wolves, and giant lions– Panthera atrox) competed for the same prey items.  However, bone collagen can decay and become contaminated, altering the accuracy of the results.  Tooth enamel is more durable, and scientists believe it provides more accurate results.  This new study concluded both saber-tooths and giant lions were ambush predators that lived in woodlands or forests and fed upon forest-dwelling herbivores such as deer, tapir, and woodland bison.  Dire wolves and coyotes (Canis latrans) lived in more open environments and chased down horses, camels, and plains bison.  The diet of saber-tooths, giant lions, and Pleistocene cougars (Puma concolor) resulted in mathmatical values of isotopic bone chemistry identical to those of modern cougars.  The diet of coyotes changed over time.  During the Pleistocene coyotes scavenged meat from megafauna.  Following the extinction of the Pleistocene megafauna, coyotes evolved toward a reduced size and fed more on bone, smaller animals, and even fruit.  The diets of timber wolves (Canis lupus) and cougars did not change following the extinction of Pleistocene megafauna.

The results of this study did not surprise me.  Saber-tooths and giant lions were built for ambushing prey in the cover of thick vegetative growth found more in woodlands than grasslands.  So of course it makes sense they preyed upon animals in those environments.

Reference:

Desantis, L; et al

“Causes and Consequences of Pleistocene Megafauna Extinction as Revealed from Ranch La Brea Mammals”

Current Biology 29 (15) 2019

Sicily During the Late Pleistocene

May 19, 2019

Over the past few weeks I read The Sicilian by Mario Puzo, author of the famous Godfather series.  He also wrote the screenplays for The Godfather and Christopher Reeve Superman movies.  His early novels were critically acclaimed but didn’t sell, so a publisher suggested he write a novel that focused on the mafia.  In his earlier novels the mafia played just a small role.  He followed this advice only to see The Godfather rejected 20 times before he finally found a publisher.  The Sicilian is every bit as good, and I’m surprised it hasn’t been adapted for the cinema.  Mario Puzo doesn’t describe the nature of Sicily much in his novel.  He does describe the island as quite arid, and he frequently mentions the “red hawks” soaring in the sky.  As a supplement to enjoying this novel I engaged in a brief study of Sicily’s natural history.

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The “red hawks” referred to in his book were probably red kites (Milvus milvus), a threatened species.

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Location of Sicily.  

Sea level fluctuations during the Pleistocene led to intermittent land bridges connecting Sicily to mainland Europe and as a consequence Sicilian flora and fauna descend from species arriving from that continent.  The location of the island in the Mediterranean Sea moderated climate, and species that disappeared from most of Europe during severe Ice Ages found refuge on Sicily.  The region is now known for mild wet winters and hot dry summers.  Average annual temperatures were likely slightly cooler during stadials.  Myrtle, oak, and cork trees covered lower elevations, while oak-beech forests occupied higher elevations.  Volcanic mountains and abundant rivers vary the landscape.

Species of large animals living on Sicily during the late Pleistocene included bison, aurochs, horse, fallow deer, red deer, roe deer, wild boar, brown bear, cave lion, hyena, wolf, and giant tortoise.  2 unique species lived on the island then–a dwarf elephant (Palaeoloxodon mnaidriensis) and the dwarf Sicilian hippo (Hippopotamus pentlandi).  The dwarf elephant was closely related to the extant Asian elephant.  It weighed just 3000 pounds, and the species also occurred on the nearby island of Malta.  Both the dwarf elephant and the Sicilian hippo became extinct shortly after man colonized Sicily about 14,000 years ago.

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Artist’s depiction of P. mnaidriensis along with a few swans.  I don’t believe it is drawn correctly to scale, unless this is the depiction of a juvenile.  Dwarf elephants were small but they weren’t this small.

People gradually eroded the quality and quantity of wildlife on Sicily, and they utterly destroyed the natural ecosystems.  Most of the island was deforested during Roman rule, leading to prolonged droughts, and the last wolves were  exterminated during the 1920s.  Though 150 species of birds live on the island, including flamingoes and several species of eagles, many are endangered.  However, the island is home to Nebrodi Mountains National Park where roe deer, wild boar, hares, Eurasian red squirrels, crested porcupines, wild cats, and foxes still roam.  Small towns founded during the Byzantine Empire are scattered throughout the park, and farmers keep rare breeds of horses and black pigs here.  The oldest chestnut tree in the world (more than 2000 years old) grows on Mt. Etna.

I’m going to read a book about the human history of Sicily next and will write a blog article about it when I’m finished.

Reference:

Bofiglo, L. et. al.

“Bio-chronology of Pleistocene Vertebrate Faunas of Sicily and Correlation of Vertebrate Bearing Deposits with Marine Deposits”

Il Quaternario 16 (1BIS) 2003

 

Pleistocene Microfauna Inherited the Earth

April 8, 2019

The biblical passage “Blessed are the meek: for they shall inherit the earth” always makes me think of the late Pleistocene megafauna extinctions.  The passage is part of Jesus’s sermon on the mount and is found in Matthew 5:5, though for some reason Luke omits it.  Most biblical scholars believe the word meek in this passage means powerless, and it represents the slaves and the small powerless Christian sect within the Roman Empire.  A large segment of the Roman Empire’s population consisted of slaves, and the Christian religion appealed to them because of the concept that their miserable lives might be rewarded in the afterlife, if they believed in Jesus.  Ironically, after the Roman Emperor Constantine made Christianity the official religion of the empire centuries later, Christians no longer acted meek–they oppressed all other religions. The late Pleistocene extinctions make me think of this passage because so many powerful animals such as giant lions, saber-tooths, short-faced bears, dire wolves, mastodons, mammoths, ground sloths, and giant bison all disappeared from the face of the earth; but small animals continued to live and were just as common as they’d always been.  Among them are 2 of the smallest mammals on earth–the southern short-tailed shrew (Blarina carolinensis) and the eastern pipistrelle (Pipistrellus subflavus).

Photo of a short-tailed shrew my cats killed last week.

The southern short-tailed shrew weighs between .5-1 ounce.  They hunt in burrows near the surface but also scurry though more permanent burrows located up to 2 feet underground.  They eat half their own weight in food everyday.  Their diet consists of worms, spiders, centipedes, insects, snails, amphibians, and mice.  During winter they can subsist on fruit, acorns, and fungi.   They are smaller than mice but can subdue them with a venomous bite.  Southern short-tailed shrew specimens have been recorded from at least 23 Pleistocene-aged fossil sites, including the Isle of Hope in southeast Georgia.

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Eastern pipistrelle.

The eastern pipistrelle weighs between .1-.3 ounce and is about the size of a large moth.  Their wingspan reaches a width of only about 2 inches.  They feed upon flying insects.  Both eastern pipistrelles and short-tailed shrews navigate in the dark by using echolocation.  Fossil specimens of this species have been found from at least 19 Pleistocene-aged fossil sites including Ladds in north Georgia.

Of course, not all species that inherited the earth are meek.  Man is a notable exception.

 

New Species of Mastodon (Mammut pacificus) Recognized

April 1, 2019

I didn’t have to search for this science news.  A link to the complete scientific paper appeared on my facebook page last week, and I knew right away this important new study was blog worthy.  Some pundits complain about the way social media intrudes on privacy, but I love how information relevant to my interests is directed to me.  If people are worried about their privacy, they should not go on the internet.

For almost 100 years paleontologists thought just 1 species of mastodon occurred in North America during the Pleistocene.  They believed the American mastodon (Mammut americanum) ranged from coast-to-coast and from the Rio Grande to Alaska.  However, 10 years ago some scientists noticed mastodon skeletal material from the Rancho Labrea Tar Pits in California differed from mastodon bones found elsewhere in North America.  Mastodon bones are relatively uncommon from Rancho Labrea where they are greatly outnumbered by mammoth (Mammuthus colombi) specimens.  Open dry environments prevailed around this site during the Pleistocene–an habitat favored by grass-eating mammoths.  Mastodons were semi-aquatic browsers, preferring to feed upon leaves, twigs, fruit, and wetland vegetation.  Within the last 10 years scientists discovered 700 mastodon bones during construction of the Diamond Lake Reservoir in Riverside County California.  This was enough material for scientists to anatomically compare California mastodons with American mastodons, and they concluded they were indeed 2 different species.

Map showing distribution of 2 mastodon species is from the below referenced paper.  Click to enlarge.  The red dots represent M. pacificus; the blue dots represent M. americanus.  Scientists aren’t sure which species ranged into Oregon.  It’s not a comprehensive distribution map for M. americanus.  I’m aware of 5 additional locations where mastodons were found in Georgia but not represented on this map.  American mastodons were more abundant in eastern North America than western.

Paleontologists named this new species M. pacificus because all specimens of this species have been found within 620 miles of the Pacific Ocean.  Apparently, this species occurred in California, southern Idaho, and possibly Oregon.  Mastodon material found in Oregon is not diagnostic, meaning there is not enough to make a species identification.  All mastodon material north of Oregon (from Washington, the Yukon, and Alaska) belongs to M. americanum, the species found throughout most of North America north of the Rio Grande.

The Pacific mastodon differs from the American mastodon in several ways.  Their molars are smaller and more narrow.  They also tend to have more sacral fused vertebrae. Pacific mastodons had 6, whereas American mastodons usually had 4 or 5 (but sometimes 6).  Pacific mastodons had thicker femurs in proportion to the length of their legs, but their tusks were smaller in diameter.

Geographical barriers likely caused the divergence of these 2 species.  Habitat favorable for mastodons was more scarce in western North America.  High mountain ranges frequently covered by glaciers during Ice Ages, and large deserts separated these 2 species.  Over time the isolated California population evolved into a different species of mastodon.

Reference:

Dooley, A.; et. al.

“Mammut pacificus sp. nov., a Newly Recognized Species of Mastodon from the Pleistocene of Western North America”

Peer J March 2019

2 New Studies of Pleistocene Lions

January 6, 2019

There were 3 species of lions living on earth during the late Pleistocene.  The African lion (Panthera leo) is the only species still extant.  The cave lion (P. spelaea) ranged across Eurasia from Britain to Beringia which included Alaska and Yukon above the Canadian Ice Sheet.  The giant American lion (P. atrox) lived in North America south of the Ice Sheet from California to Florida.  Some taxonomists formerly thought the 3 lions were the same species, but recent analysis of anatomy and genetics determined they were 3 distinct species.

2 new studies of Pleistocene lions were published last year.  The first study described an unusually large lion skull found in Natodermi, Kenya.  This specimen is estimated to be 196,000 years old. On average cave lions and giant American lions were larger than African lions.  P. atrox was the largest species of lion, averaging 25% larger than African lions, and 1 specimen is estimated to have weighed over 1000 pounds.  (See https://markgelbart.wordpress.com/2017/01/31/panthera-atrox-the-1007-pound-giant-lion/ )   However, the specimen described in this new paper (catalogued as #KNM-ND59673) belonged to an individual that may have been larger than any cave lion specimen ever described and even larger than all but 2 known American lion specimens.  The size comparison estimates in this paper were based on dental dimensions.  The authors of this paper believe this individual was part of an extinct population that grew to a larger size because they hunted an extinct species of large buffalo (Syncerus antiquus).  They think it was a subspecies of African lion related to the ancestors of the 2 regional haplotypes of lion that still occur today.  Genetic evidence suggests northern lions diverged from an ancestral population of lions 147,000 years ago, while southern lions diverged 189,000 years ago.  This specimen was found on the border between the 2 modern haplotypes.  Although they don’t think it was a distinct species, they can’t completely rule it out–there just isn’t enough evidence.  It seems likely some Pleistocene African lions were just as large as the other 2 species.  Lions originally evolved in Africa but fossil evidence from that continent is more rare than in Eurasia and North America.

 

196,000 year old African lion skull.

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Pleistocene lions may have grown larger in Africa to help them bring down this large extinct species of buffalo.

The 2nd study described 4 specimens of cave lion found in Medvedia Cave located in the Zapadne Tatry Mountains.  These mountains border northern Slovakia and southern Poland. Referring to this species as the “cave” lion is misleading.  Most individuals never went inside a cave during their entire life.  A cave environment is just 1 of the rare places where their remains could be preserved.  Medvedia Cave is the highest altitude that a lion fossil has ever been found.  The authors of this paper think lions searched through caves for hibernating bears, and groggy bears may have been an important part of high altitude lions’ diets because other substantial prey was scarce here.  Some scientists think cave lions were solitary hunters or perhaps hunted in pairs, unlike social African lions that live in large prides.  I disagree with this notion.  Adult male lions grow too large and bulky to hunt prey effectively, and they depend upon females to bring them food.

Lions were more widespread during the Pleistocene because human populations were sparse.  Humans have outcompeted lions since then.  If not for the rise of humans, lions would still be just as widespread as they used to be.

Reference:

Manth, F. ; et. al.

“Gigantic Lion, Panthera leo, from the Pleistocene of Natodermi, eastern Africa”

Journal of Paleontology 92 (2) Novemeber 2018

Sabol, Martin; Juraj Gullar and Jan Harrat

“Montane Record of the Late Pleistocene Panthera spelaea (Goldfuss 1810) from Zapadne Tatry Mountains (northern Slovakia)”

Journal of Vertebrate Paleontology  38 (3) 2018

See also: https://markgelbart.wordpress.com/2016/01/07/uf9076-a-complete-skull-and-jaws-of-a-giant-lion-panthera-atrox-found-in-the-ichetucknee-river-florida/

There was No Such Species as the Fugitive Deer (Sangamona fugitiva)

December 16, 2018

During 1920 Oliver Hay, a noted paleontologist of that era, named a new species based on a tooth discovered in a Tennessee Cave 35 years earlier.  He believed it was from an extinct species of deer, and he gave it the scientific name of Sangamona fugitive because he thought it may have been common during the Sangamonian Interglacial, though most specimens of this proposed species came from deposits dating to the Wisconsinian Ice Age.  For the next 60 years scientists assigned additional specimens found at fossil sites located in Tennessee, Illinois, Maryland, and Iowa to this species.  The fugitive deer was thought to be a species intermediate in size between a white-tail deer and an elk.  However, during the early 1980s a paleontologist by the name of George Churcher looked at all the specimens assigned to this species and determined they were actually the bones of white-tail deer, elk, or caribou.  Some were from large white-tails and others were from small elk, explaining why they seemed to fall between the range of the 2 species.  Churcher declared Sangamona fugitive an invalid species.  No such animal ever existed.  Taxonomists refer to this as a nomen nudem or naked name because it was assigned to a non-existent animal.

I was unaware of Churcher’s study when I wrote about the fugitive deer in my book and in a few of my earliest blog entries.  His paper is buried in the middle of an obscure special bulletin of the Carnegie Museum.  I did come across this paper a few years ago, but I never felt motivated to write about it until now.  I’m in the middle of researching future topics for my blog and ran into a delay with a couple I had planned, so I finally decided to note this old mistake that originated from a long dead paleontologist.

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Most bones mistakenly assigned to the fugitive deer actually belonged to white-tail deer or elk.

The fossil record suggests there were just 4 species of deer living in southeastern North America during the late Pleistocene.  White-tail deer lived throughout the entire region.  Caribou and the extinct stag-moose (Cervalces scotti) periodically colonized the upper south during cooler climatic stages of the Ice Age.  Elk probably didn’t enter the upper south until 15,000 years ago.  Mule deer may or may not have occurred in western Arkansas.  A single specimen of the South American marsh deer found in Florida was probably a misidentified white-tail deer bone.  (See: https://markgelbart.wordpress.com/2013/02/28/sabertooth-cave-in-citrus-county-florida/ )

Reference:

Churcher, George

“Sangamona: the Furtive Deer”

Bulletin of the Carnegie Museum: Contributions in Memorial to John Guilday 1984

ABC Bears

November 5, 2018

During the Ice Age the coast of southeast Alaska was studded with ice floes and perfect habitat for seals and polar bears.  The interior of Alaska was mostly grassy steppe, the preferred habitat of brown bears.  About 16,700 years ago the icy habitat along the southeast coast of Alaska began to melt and polar bear populations became stranded on Admiralty, Baranet, and Chichagof Islands; also known as the ABC islands.  Here, the habitat began to become more favorable for grizzly bears, and young males looking for new territory not already occupied by adult males colonized the islands.  A genetic study of 1 specimen from this island group determined these colonizing male brown bears mated with female polar bears, creating an hybrid population  (Ursus arctos x U. maritimus).  Gradually, the population of brown bears swamped the DNA of this region, so today polar bear DNA makes up just 6% of their X  chromosome (the female chromosome is XX; the male is normally XY).  Polar bear DNA has also been found in specimens of the extinct Irish brown bear.  DNA evidence suggests polar bears diverged from brown bears about 4 million years ago, but there has been periodic hybridization in regions where the 2 species overlap.

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Location of the ABC islands.

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Top 2 photos are polar bear/brown bear hybrids in captivity.  Bottom right is a polar bear; bottom left a brown bear.  The 2 species rarely do hybridize in the wild.

A few months ago, Discovery Channel aired a program about the ABC bears that I lambasted in this blog article https://markgelbart.wordpress.com/2018/06/04/the-fear-island-special-that-aired-on-animal-planet-last-night-was-full-of-shit/ .  Previously, Discovery Channel has aired programs about Bigfoot, mermaids, and the extant existence of a 60 foot long extinct species of shark.  I assumed this program was completely bad pseudo-science, but 1 of my readers alerted me to the scientific merits of this program and also informed me that I wrongly assumed the ABC islands were the same as the Kodiak islands.  The Kodiak islands are on the other side of the Gulf of Alaska, so I errored geographically by hundreds of miles.  And the expedition on this program did have scientific merit because they were seeking just the 2nd DNA sample from an ABC bear.  However, I still think this program was full of shit…just not as full of shit as I initially assumed.  Here is why I stand by my first opinion:

1. The participants acted as if they were the first researchers to ever obtain DNA evidence from a bear on the island, though a study of 1 specimen had already been published.  They already had a good idea what they were going to find, and it was not a great mystery as they promoted.

2. The Indian guide claimed he saw 6 bears ceremonially bury another dead bear.  What unscientific bull crap.

3. I don’t buy the size estimate claim.  It was based on an up close trail cam photo.  Weigh it or just shut up.

Reference:

Cahill, J; et. al.

“Genetic Evidence for Island Populations Conversion Resolves Conflicting Theories of Polar Bear Evolution”

PLOS Genetics 2013

 

Pleistocene Pine Voles (Pitymys pinetorum)

October 16, 2018

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.

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

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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