Archive for the ‘Pleistocene Mammals’ Category

The Unknown Mating Habits of Saber-toothed Cats (Smilodon fatalis)

February 5, 2017

The average male saber-toothed cat was only slightly larger in overall body size than a female saber-tooth, but they had significantly larger mandibles and upper canines (the fangs).  This is in contrast to most species of cats today.  Most male cats and especially lions are much larger than the average female of their species.  The mating habits of Smilodon are completely unknown, and we can only speculate about them based on the knowledge that they differed in size above the neck, but not much elsewhere aside from the sexual organs.

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Smilodon had low sexual dimorphism in body size, but males had significantly larger mandibles and upper canines.  Did males share their larger kills with females as way to attract them?

I believe saber-tooth mating habits may have been notably different from those of all extant species of cats.  The saber-toothed and the scimitar-toothed cats ( Dinobastis or Homotherium ) belonged to an extinct subfamily of cats known as the Machairodontinae.  The Machariodontinae diverged from all other cats an estimated 13 million years ago, very early in cat evolution, and they have no close living relatives today.  They were more closely related to other carnivores than modern day species of cats are.  Perhaps they lived in matriarchal societies like the spotted hyena ( Crocuta crocuta ), another species that shows low sexual dimorphism (the females are actually slightly larger than the males).  Or maybe, as in the wolf ( Canis lupus only the dominant male and female of the pack were allowed to mate.  However, scientists disagree over whether saber-toothed cats were social or solitary animals.

Some scientists argue evidence from the La Brea Tar Pits of severely injured saber-tooths that survived traumatic debilitating injuries suggests they must have lived in groups.  But others believe that even a severely injured saber-tooth could have lived for a long time by scavenging.  A saber-tooth in a bad mood due to pain could have easily intimidated smaller predators from their kills. Moreover, their small braincases also indicates they didn’t live in groups.  I suspect they were solitary cats, though mothers probably hunted cooperatively with nearly grown cubs when she was training them how to hunt.

The males were able to bring down larger prey than the females because their bites, aided by the larger jaws and fangs, were deadlier.  Perhaps this was an element of their mating system.  Females that came to scavenge the male-killed prey were tolerated by the males, and the heavy meal caused them to go into instant heat.  Maybe females followed the most successful hunting males with the frequent nutritious meals triggering more frequent ovulation.

I’ve always been fascinated over how recently this strange exotic animal became extinct–only ~10,000 years ago.    It’s frustrating not to be able to know more about how it lived.  Relying on guesswork is just not as satisfying as knowing.

References:

Christiansen, P.; and John Harris

“Variation in Craniomandibular Morphology and Sexual Dimorphism in Pantherines and the Sabercat Smilodon fatalis

Plos One Oct 2012

Meachen-Samuels; J.A.; W.J. Binder

“Sexual Dimorphism and Ontogenetic Growth in the American Lion and Sabertoothed Cat from Rancho La Brea”

Journal of Zoology 2010

Mammoths and Mastodons were Year Round Residents of the Ohio River Valley during the Late Pleistocene

January 27, 2017

The bones and teeth of an extinct animal provide scientists with information about the life history of that particular individual.  Recently, 2 scientists analyzed the chemistry of 8 mammoth ( Mammuthus columbi ) and 4 mastodon ( Mammut americana ) teeth collected from Hamilton County, Ohio and Bullitt and Gallatin Counties, Kentucky–in other words, the Cincinnati area.  They determined 11 of these animals spent their entire lives in what was to become the Cincinnati area.  They also learned 7 of the mammoths ate different plant foods than the mastodons, but the diet from 1 individual mammoth did overlap with mastodon diets.

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Hamilton County, Ohio

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Mammoths and Mastodons lived year round in the Ohio River Valley.  They were 2 completely different species of proboscidean.

Scientists are able to determine where an animal lived during its lifetime by measuring the ratio of strontium and strontium isotopes in their teeth.  Strontium leaches from local bedrock into the water supply, and animals absorb the strontium into their bones when they drink.  Different geographical regions exhibit different ratios of strontium isotopes, so it’s possible to figure out where an animal spent time during its life.  A previous study of mastodon and mammoth teeth collected from Florida determined mastodons there migrated back and forth from central Florida to central Georgia, while Florida mammoths did not migrate.  But this study suggests most of the mastodons that lived in the Ohio River valley did not migrate.  However, there were exceptions.  The strontium ratio from 1 specimen indicated this individual wandered north from either north Georgia or southern Tennessee to the Ohio River valley.  The authors of this study estimated this could have been accomplished in as little as 5 days based on how fast modern elephants can travel.

The bone chemistry tells us mammoths mostly ate grass, while mastodons ate plants that grew in forested environments.  But again there was 1 exception–1 mammoth that fed upon forest vegetation.  During the Last Glacial Maximum much of this region was a cool arid steppe environment.  After the nearby ice sheet retreated, the steppe was transformed into an open spruce parkland, then eventually an oak and hardwood dominated forest.  This mammoth apparently adapted to the latter changes.

Mammoths and mastodons had no need to migrate away from the Ohio River.  The rich floodplain habitat and numerous mineral licks provided enough nutrition to support year round populations of both.

Reference:

Baumann, Eric; and Brook Crowley

“Stable Isotopes Reveal Ecological Differences among now Extinct Proboscideans from the Cincinnati Region, USA”

Boreas 2015

Donald Grayson’s Disingenous Case Against Overkill

January 23, 2017

I almost chose not to read Donald Grayson’s most recent book, Giant Sloths and Sabertooth Cats: Extinct Mammals and the Archaeology of the Ice Age Great Basin.  Grayson is a long time skeptic of the hypothesis that man overhunted Pleistocene megafauna to extinction, and he has authored and co-authored a number of papers explaining his position.  In my opinion overhunting by man is the only explanation for the extinction of Pleistocene megafauna that makes sense.  I’ve read his papers and consider his arguments highly illogical and unfair.  But I did purchase his book because I try to absorb all the knowledge I can about my favorite subject–the late Pleistocene ecology of North America.  I don’t have to agree with an author about everything to enjoy their work.  I saw his chapter on extinction was short, just a small portion of the book, and I assumed he would simply rehash his tired old case against overkill.  However, I was shocked at the way he misrepresented the results of a paleoecological study.  He implies the results of this study support climate change models of Pleistocene megafauna extinctions.  In fact this paper specifically states the opposite.

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Donald Grayson’s newest book.  His chapter on extinction is marred by gross deception.

Don Grayson, photo by Mary Levin, UW Photography, 2011

Donald Grayson is an archaeology professor at the University of Washington.  

On page 287 of the above book, Grayson wrote “…paleoecologist Jacquelyn Gill and her colleagues took a close look at tiny bits of Ice Age history extracted from 3 lakes and marshes in New York and Indiana.”    Grayson fails to mention the data from the lakes in New York was gathered in a study led by Guy Robinson (1).  (I will number the studies mentioned in this blog post and list them below.)  Guy Robinson’s team took samples of sediment from some New York lakes and marshes, radiocarbon dated different chronological layers of it, and measured and analyzed the volume of pollen, charcoal, and dung fungus spores in each layer.  The volume of dung fungus spores is used as a proxy to estimate populations of megafauna.  They determined local extinctions of megafauna were staggered throughout 2 thousand years, and they concluded this ruled out climate change as a cause of the megafauna extinctions.  If climate change caused the extinctions, they believed the extinctions at these different sites would be simultaneous.  Instead the local extinctions occurred at different times at different sites, and it appears as if nomadic humans were overhunting megafauna at 1 site, then moving on to another, though these local extinctions occurred shortly before the Clovis cultural era.  Increases in charcoal while megafauna populations were declining is additional evidence of probable human impact.  Jacquelyn Gill, the lead author of the paper (2) Grayson referred to in his book,  details a similar study of an Indiana lake.  The authors of this study also found that megafauna populations declined before the Clovis cultural era but also before climate caused changes in the local plant composition.  They believe human impacts are still a “plausible” cause of megafauna extinction, and they wrote “our data thus rule out the hypothesis that (i) climate-forced changes in vegetation drove the megafaunal decline, and (ii) no-analogue plant communities were created by megaherbivory.”  Megafauna became locally extinct here before the pollen evidence suggests changes in the plant community occurred.  They believe humans can still be implicated in megafauna extinctions at this site because increases in charcoal indicated humans were setting fire to the landscape during the period of megafauna decline, and there is evidence of human butchery of mammoths in southeastern Wisconsin during this same time period, suggesting that humans were likely hunting them at this location as well.

It is very dishonest of Grayson to imply these studies support climate-change models of extinction when the authors of these studies specifically state the opposite.  He should have at least informed his readers of their conclusions and explain why he has a different interpretation of the data.  The authors of these studies do note that megafauna decline occurred during a warm phase of climate, but they believe, if climate played a role, it had to be some other mechanism besides climate-driven changes in the environment.  The accepted logic behind climate change models of extinction is that changes in climate decreased the plant foods necessary to maintain viable populations of megaherbivores.  These studies show this is not the case.  Moreover, fossil coprolites show the plants Ice Age megafauna ate are still common on the landscape today, and isotopic studies indicate they were not picky feeders, but instead ate a wide variety of foods.  I think the warm climate phase provided a greater variety of edible plant foods for humans, thus increasing human populations which in turn was detrimental to megafauna.

There are many regions in North and South America where the environment did not change substantially during the most recent glacial-interglacial transition including the pampas of Argentina, southern California, and southeastern North America, especially Florida and the coastal plain.  Climate change models of extinction just don’t make sense in these regions.  Most species of megafauna enjoyed continent wide distributions, and they endured 30 glacial-interglacial transitions over the past 2 million years without suffering extinctions, yet they did become extinct about the same time man appears in the archaeological record.  This can’t be coincidence.

Grayson focuses his arguments against overkill on the Clovis blitzkrieg model of extinction.  This model proposes humans rapidly overhunted megafauna to extinction within the 500 year period of the Clovis cultural era.  There is another model of overkill: humans were responsible for overhunting megafauna, but it took place over several thousand years and also involved a change in fire regime and other human impacts.  This is known as the protracted overkill model and it is the one I favor.  Grayson ignores this model.  He doesn’t acknowledge the likelihood that pre-Clovis humans impacted megafauna populations.  I’m sure he would point out the lack of archaeological evidence for this.  His main objection to the blitzkrieg model is also a lack of archaeological evidence…he believes there are not enough kill sites (direct evidence that humans killed a beast) to justify the overkill hypothesis.  This objection is unreasonable.  99.999…etc% of the individuals of a species that ever lived left no fossil evidence at all.  It is ridiculous to expect to find fossil evidence of the last individuals of a species that just happened to be killed by men.  Moreover, Grayson never quantifies how many kill sites archaeologists would need to find before he would be convinced humans were responsible for the demise of the megafauna.  He needs to put an exact number on it or cease his objections.  Despite the odds against it, there are numerous kill sites and evidence of human-butchered megafauna bones.  Grayson dismisses over half of them, sometimes unfairly, though sometimes his skepticism is warranted.

Grayson falsely claims the overkill hypothesis has “little going for it” and he sounds annoyed on pages 279 and 280 of his book when he laments its acceptance in the popular media.  He might be annoyed because in recent years the  overwhelming number of paleoecological and statistical studies suggest man at least played some role in megafauna extinctions.  Grayson glosses over a statistical study led by G.W. Prescott (3) that determined both man and climate played a role in the end Pleistocene extinctions.  But 2 recent studies of worldwide extinction chronology (4) (5) determined extinctions are more closely tied to human expansion than climate change.  In the study led by C. Sandom they note extinctions have been severe in climatically stable regions.  They write: “Human arrival was a necessary factor for extinctions, whereas climate variation was a contributory one, enhancing regionally the effects of anthropogenic impacts on additive rather than synergistic ways.”

References:

(1) Robinson, G.S. ; L.P Burney and D.A. Burney

“Landscape Paleoecology and Megafaunal Extinction in Southeastern New York”

Ecological Monographs 2005

(2) Gill, J.L.; J.W. Williams, S.T. Jackson, K.B. Lininger, and G.S. Robinson

“Pleistocene Megafauna Collapse, Novel Plant Communities, and Enhanced Fire Regimes in North America

Science 2009

(3) Prescott, G.W. et. al.

“Quantitative Global Analysis of the Role of Climate and People in Explaining Late Quaternary Extinctions”

PNAS 2012

(4) Aravjo, Bernardo et. al.

“Bigger Kill than Chill: the Uneven Roles of Humans and Climate on Late Quaternary Megafaunal Extinctions”

Quaternary International 2015

(5) Sandom, C. et. al.

“Global Late Quaternary Megafauna Extinctions Linked to Humans, not Climate Change”

Proceedings of the Royal Society 2014

http://rspb.royalsocietypublishing.org/content/281/1787/20133254

 

A Recent Study of Pleistocene Armadillo DNA Yields 2 Surprising Results

January 19, 2017

An extinct species of armadillo ( Dasypus bellus ) ranged throughout southeastern North America during the Pleistocene.  (A much larger species, Holmesima septentrionalis, was restricted to Florida and the lower coastal plain.)  Scientists have described D. bellus , known by the common name of beautiful armadillo, as being remarkably similar to the extant 9-banded armadillo ( D. novemcinctus ).  The most notable difference between the 2 species is size–the beautiful armadillo was twice the size on average as the 9-banded armadillo.  The latter species began to expand its range into southeastern North America from Mexico within the last 150 years, and today is very common and on the increase in the region.  In a previous blog entry I hypothesized the 9-banded armadillo was a dwarf mutation of the beautiful armadillo, and it was currently recolonizing former parts of its range.  (See: https://markgelbart.wordpress.com/2012/08/19/is-the-9-banded-armadillo-dasypus-novemcinctus-a-dwarf-mutation-of-the-pleistocene-species-dasypus-bellus/ ) However, scientists were recently able to extract DNA from 2 Pleistocene-aged armadillo specimens, and they determined the history of the 2 Dasypus species is more complicated and even more interesting than previously thought.

An armadillo I saw at Scull Shoals State Park, Georgia.  2 species of similar armadillos occupied southeastern North America during the Pleistocene including this 1.

Scientists extracted DNA from an armadillo specimen found in Brynjulfson Cave, Missouri and from another specimen excavated from Medford Cave, Florida.  (They tried many other specimens but these were the only 2 that still yielded viable DNA.)  They determined the DNA of the Missouri specimen was distinct enough from modern 9-banded armadillo DNA to be considered a distinct species.  So much to my surprise, the beautiful armadillo is not the same species as the 9-banded armadillo.  But the Florida specimen held an even bigger surprise…it was a 9-banded armadillo and it dated to over 10,000 years ago.  This means both beautiful armadillos and 9-banded armadillos lived in southeastern North America during the Pleistocene.  The former went extinct while the latter was temporarily extirpated from the region but has just recently made a comeback.

The scientist who originally described the specimen from Florida noted its similarity to the 9-banded armadillo but chose to identify it as a beautiful armadillo because that was the species thought to occur there during the Pleistocene.  This individual was as large as a beautiful armadillo, showing that size alone is not enough to diagnose correct species identification.  Unfortunately, most subfossil specimens no longer contain DNA due to permineralization or decay.  All the specimens labeled ” D. bellus ” in the scientific literature should be re-labeled as ” D. species ” until scientists make a more detailed anatomical analysis of the genus, so that these 2 species can be better distinguished.

So why did the 2 species disappear from southeastern North America near the end of the Pleistocene?  Cold arid climate cycles probably caused range reductions and local extinctions, but armadillos likely re-expanded during warmer wetter climate phases.  Today, 9-banded armadillos may use manmade roads to facilitate their range expansion because it’s less strenuous to travel along cleared roadsides (though dangerous because highways are littered with armadillo corpses). During the Pleistocene armadillos probably followed trails trampled clear by herds of megafauna. This facilitated range expansion during favorable climate cycles.  The extinction of the megafauna may have played a role in the demise of armadillos that could no longer expand their range after climate deterioration caused extirpations. This isn’t a completely adequate explanation–Florida never got too cold and dry for armadillos.  The authors of the below referenced study suggest frequent manmade fires may have been detrimental to armadillos.  Native Americans set fire to the woods annually.  Modern day fire suppression may be another reason 9-banded armadillos have been able to recolonize former territory.

Reference:

Shapiro, Beth; Russell Graham, and Brandon Letts

“A Revised Evolutionary History of Armadillos (Dasypus) in North America Based on Ancient Mitochondrial DNA”

Boreas August 2014

 

 

 

 

Pleistocene Mammals of the Levant

January 14, 2017

Long before the stories in the bible supposedly took place, the Levant was a beautiful wilderness sparsely populated by humans.  The Levant is the region encompassing the modern day boundaries of Israel, Lebanon, Syria, Jordan, and Iraq.  For millions of years climatic fluctuations have caused a waxing and waning of 2 different types of environments here–Mediterranean evergreen oak woodlands and Irano-Turanan steppe consisting of deciduous oak trees and grassy understories.  Habitat for both forest species and grassland fauna has been available during every climatic stage.  The region is also a gateway between Eurasia and Africa, so animals from 3 continents converge here, making it rich in diversity.  African species such as elephants, giraffes, rhinos, hippos, gazelles, hartebeest, warthog, macaque, hyena, lion, leopard, cheetah, and Cape Hunting dog formerly lived side by side with Eurasian species including aurochs, bison, horse, ass, camel, deer, wild boar, ibex, wolf, and brown bear.

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Map of the Levant.

The fossil record suggests the fallow deer ( Dama dama ) was the most common large herbivore in the Levant for over 2 million years.  This species prefers fairly dense woodlands, so their abundance in the fossil record surprises me because I always think of this region as arid.  However, during Ice Ages, the climate in the Levant was cooler and rainier than it is today, though drier climate phases did occur cyclically.  The extinct giant deer ( Megaloceros giganteus ) and elk ( Cervus sp. ), known as red deer in Europe, also made the Levant their home.  The wild ibex ( Capra aegargus ), ancestor of the domestic goat ( C. hircus ), was common on rocky hillsides; gazelles, hartebeest, and an extinct species of warthog roamed the grassy plains.

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Fallow deer.

During warmer climate cycles hippos inhabited Lake Kinnaret.  Long chains of lakes often existed along the Jordan River, and during some climatic stages Lake Kinnaret joined the extinct Lake Amora and the Dead Sea to become 1 giant primeval lake known as Lake Lisan.  Oddly enough, geologists believe Lake Lisan was a freshwater lake in the part that covered the current site of Lake Kinnaret, while the rest of the lake was salty.

A primitive genera of elephants known as stegodon became extinct in Africa about 1 million years ago, but they still lived in the Levant for hundreds of thousands of years past their African extinction.  Stegodon survived until the end of the Pleistocene in southeastern Asia.  Two species of elephants roamed the Levant during the Late Pleistocene–the steppe mammoth ( Mammuthus trogontherii ) and the straight-tusked elephant ( Paleoloxodon antiquus ).  The former evolved into the woolly mammoth during a later Ice Age.  Straight-tusked elephants were a temperate species that couldn’t survive the climate deterioration of the last Ice Age in most of Eurasia.  However, the Levant probably provided a refuge for this species then.  I hypothesize humans overhunted straight-tusked elephants to extinction in their final refugia.  And I believe the same fate befell the temperate species of rhino ( Stephanorhinus hemiotoechus ) that occurred throughout Eurasia.  The Levant likely served as a refuge for these 2 species of megafauna during previous glacials, but human populations and/or hunting skills increased enough to permanently eliminate these slow breeding animals sometime within the timespan of the most recent Ice Age.

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Stegodon.

The lion ( Panthera leo ) that lived in the Levant was the same subspecies as the Asiatic lion found today in 1 small area of India–the Gir Forest.  This big cat survived in remote regions of the Levant until the 19th century.  There is still a small population of leopards in the Levant.  Two species of wolves ranged through the Levant–the timber wolf ( Canis lupus ) and the Egyptian wolf ( C. lupaster ).   Though the latter species occasionally interbreeds with golden jackals ( C. aureus ), a genetic study determined they are more closely related to C. lupusA single specimen of Cape Hunting dog ( Lycaon pictus ) was excavated from Hayonim Cave, Israel.  The paper written about this site incorrectly states this as the only fossil material of Cape Hunting dog ever found outside Africa, but fossils of closely related species have been discovered in Alaska and Texas.

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Asiatic lions in Gir Forest–the same subspecies lived in the Levant until the 19th century.

Pleistocene megafauna suffered fewer extinctions in the Levant than in the Americas.  Wildlife there co-occurred for a longer time with low populations of primitive humans and had time to evolve better avoidance strategies.  Moreover, many Levant species that did become extinct in the wild still live on as domesticated descendents.  Nevertheless, most of the megafauna species were extirpated from the Levant by the 20th century.

References:

Marder, Ofer; et. al.

“Mammal Remains of Rantis Cave, Israel and mid to late Pleistocene Paleoenvironment and Subsistence in the Levant”

Journal of Quaternary Science 2011

Stimer, Mary; and Ofer Bar-Yozef

“The Fauna of Hayonim Cave, Israel: A 200,000 Year Record of Paleolithic”

American School of Prehistoric Research 48 2009

The Super Squirrel

January 3, 2017

The eastern gray squirrel ( Sciurus carolinensis ) outlasted many of the magnificent extinct species of Pleistocene megafauna because they are well adapted to survive in environments modified by man.  They are just as much at home in suburbs, city parks, and 2nd growth forest of the countryside as they are in the middle of a pristine wilderness.  Unlike western gray squirrels ( S. griseus ), they are not shy around man and will nest in backyards or even attics.  They are nimble squirrels, able to jump from tree top to tree top in the young dense forests that replace abandoned agricultural lands.  And they have a unique way of spreading their populations.  Every September, juvenile eastern gray squirrels begin to expand their range and forage for acorns and nuts.  After they have spent enough time  burying acorns in a certain area, they establish an home range there.  This process is known as the “September shuffle.”  During colonial times when there were still vast tracks of timber, this September shuffle could seem like a massive migration, especially during years of poor mast production following a year of heavy mast production that increased squirrel numbers. (See: https://markgelbart.wordpress.com/2012/08/24/squirrel-migrations/ )

Eastern gray squirrels thrive everywhere they’ve been introduced–England, Ireland, Italy, South Africa, western Canada, and Australia (where they were eventually eradicated by man).  Much to the consternation of English naturalists, they have almost completely displaced native European red squirrels ( S. vulgaris ) on the British Isles.  There are several possible reasons for this displacement.  Eastern grays are carriers of a virus that may be fatal to European red squirrels.  They may also disrupt red squirrel mating and outcompete them for food, and they are simply better adapted to living adjacent to people.  But the most compelling ecological explanation involves comparing European and American Ice Ages.

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The American eastern gray squirrel in Brandon Hill Park, Bristol, England.  Gray squirrels are better adapted to living in deciduous woodlands than native red squirrels and they are displacing them.

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The Eurasian red squirrel is being displaced by introduced American gray squirrels in Great Britain and Italy.

In Europe glaciers covered a greater percentage of territory than they did in North America.  Most of the unglaciated region consisted of grassy or shrubby mammoth steppe with pockets of spruce and pine growing in moist protected areas.  Some southerly lowlands supported more extensive conifer forests.  The deciduous oak forests that dominate most of Europe today were restricted to narrow strips along the Mediterranean coast.  Because glacial stages were 5-10 times longer than interglacials, European red squirrels became better adapted to live in conifer forests.  However, in North America, even during the severest stadials, there were always extensive oak and oak/pine forests that supported large populations of gray squirrels.  Eastern grays evolved the ability to digest acorns better than red squirrels can.  Although eastern grays are not native to Europe, they are a better fit for the interglacial oak forests that exist there today.  Ecological displacement of 1 species by another has occurred thousands of times during earth’s history.  People may object to the displacement of European reds by eastern grays because man played a role in the introduction of the latter, but it is not unnatural or detrimental to the overall ecosystem in this case.

Eastern grays along with California ground squirrels, introduced fox squirrels ( S. niger ), and turkeys are displacing and outcompeting western gray squirrels on the Pacific coast of North America.  All seem to be better adapted to anthropogenic environments.  Western grays are now restricted to deep wilderness preserves.  Introduced eastern gray squirrels are also displacing American red squirrels ( Tamiasciurus hudsonicus ) in British Columbia.

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The American red squirrel is being displaced by gray squirrels in some parts of its range as well.

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Taxidermic mounts of eastern and western gray squirrels. The western is larger with a bushier tail.  Introduced Eastern gray squirrels and fox squirrels, as well as native California ground squirrels and turkeys are outcompeting western grays in suburban areas of California heavily modified by man.

Eastern gray squirrels have co-existed with fox squirrels for hundreds of thousands of years but are more common in many areas, including Richmond County, Georgia where I live.  Eastern grays quickly recolonize agricultural land replaced by dense 2nd growth forest, while fox squirrels prefer mature forests with widely spaced trees.  Because most of southeastern North America was clear cut between 1865-1945, gray squirrels have been quicker to return and spread throughout their range.  Without human introduction fox squirrels may never return to formerly clear cut land.

Eastern gray squirrels boldly live next to people and their unique September shuffle makes them a super squirrel, able to expand their populations and survive where other squirrels can’t.

Reference:

Bruemmer, Corrie; Peter Lurz, Karl Larsen, and John Gurnell

“Impact and Management of Alien Eastern Gray Squirrel in Great Britain and Italy: Lessons from British Columbia”

Proceedings of the Conference on the Biology and Management of Species and Habitats at Risk 1999

 

 

Black Bear (Ursus americanus) Diversity during the Pleistocene

December 19, 2016

Fossil evidence suggests North American black bears evolved from an Holarctic population of bears about 3 million years ago.  The founding preceding species is known as Ursus abstrusus in North America and Ursus minimus in Eurasia but they were likely the same animal.  Eurasian black bears ( Ursus thibetanus ) diverged from North American black bears during some climate phase when the ancestral populations became geographically isolated.  Before this divergence moderate climate allowed forested conditions to exist across the Bering land bridge.  But deteriorating climate transformed the land bridge to tundra when it wasn’t submerged under the Bering Sea.

Genetic evidence indicates western populations of North American black bears diverged from their eastern counterparts about 1.8 million years ago.  This corresponds with the beginning of the Pleistocene.  Although weak Ice Ages occurred during the preceding Pliocene, they became much more severe at the onset of the Pleistocene.  Glaciers covered most of Canada and the upper elevations of the Rocky Mountains, blocking gene flow between eastern and western populations of black bears.  Some mixing occurred (and is presently occurring) during interglacials, but because glacial climate phases are 5-10 times longer than most interglacials, isolation between eastern and western populations has  been the norm.

An ancient isolated population lives along the coast and islands of British Columbia.  Glaciers covered most of British Columbia during the Last Glacial Maximum but a strip of land along the coast, including the now submerged continental shelf, hosted a temperate rain forest with a population of black bears.  These forests were probably snow-covered for much of the year, an environmental condition that may have selected for white bears.  The white color may also help improve success hunting for salmon.  The lighter color is harder for the fish to see during the day. Today, this region is home to the highest incidence of white-coated black bears, variously known as Kermode or spirit bears.  On mainland British Columbia 1 in 40 black bears have white coats, while on some of the British Columbian islands 1 in 8 have white coasts.  (They are not albino.)  White bears in most black bear populations are extremely rare in other regions, though when the species was more common there were occasional individuals with white coats.  A white-coated bear was killed in a 1760 ring hunt (See: https://markgelbart.wordpress.com/2014/07/27/the-pennsylvania-mammal-holocaust-of-1760-a-rare-record-of-an-old-fashioned-varmint-drive/ )  Black bears may also be cinnamon, blonde, or even blue.

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The Kermode or Spirit bear–a white color phase of the black bear most common along the coast of British Columbia.  It’s an Ice Age relic population.

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Blue color phase cubs of a black bear mother.

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Cinnamon color phase mother with black and blonde (?) phase cubs.

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Blonde black bear.

During the Pleistocene before humans reduced black bear populations, many grew as large as grizzlies, and they had a much greater genetic diversity.  However, they competed with giant short-faced bears ( Arctodus simus ) and Florida spectacled bears ( Tremarctos floridanus ).  In open environments I think the former may have excluded black bears much in the same way grizzlies kept black bears from ranging into California valleys.  Spectacled bears co-existed with black bears in the same forested habitats for over a million years, and the environment in many places was rich enough to support both species.  Black bears were more adaptable than both of these now extinct species.  I hypothesize that unlike giant short-faced bears, they learned to fear man.  The ability to hibernate during cold weather also made them more widespread and successful than spectacled bears which were probably limited to regions with warmer climate.

Reference:

Marshall, H.D. and K. Ritbad

“Genetic Divergence and Differentiation of Kermode Bear Populations”

Molecular Ecology 2002

Wooding, Stephen and R. K. Ward

“Phylogeography and Pleistocene Evolution in North American Black Bear”

Molecular Biology and Evolution  1999

The Former Abundance of California Grizzly Bears (Ursus arctos)

December 13, 2016

An image of a grizzly bear adorns the California state flag, although the species hasn’t been seen in the state since 1924.  The irony of a state symbol that can no longer be found locally is emblematic of the environmental decline suffered nationwide because there are many place names (Panther Creek, Elk Knob, Pigeon Mountain, etc.) all across the country named after animals long absent from that particular region.  Biologists believe existing wilderness in California could support a population of 600 grizzly bears, but the U.S. Fish and Wildlife Service rejects proposals to reintroduce them.

Though a grizzly bear is on the California state flag, authorities refuse to allow reintroduction of the species to the state, since its extinction there circa 1924.

 

“Thieving Grizzlies in a California Wheat Field” by Albert Pennoyer.

Grizzly bears, the same species as the Eurasian and Alaskan brown bear, crossed the Bering Land Bridge ~50,000 years ago.  Fossil and genetic evidence suggests they colonized North America before the Last Glacial Maximum when glaciers expanded and blocked the route between what today is Alaska and the rest of the continent.  Grizzly bear subfossils dating to the late Pleistocene have been found as far east as Kentucky, Ohio, Ontario, and Quebec; but the range of this species has retracted westward since the end of the Pleistocene.  Grizzly bears probably roamed California for 40,000 years before their extirpation there.  They did survive the end Pleistocene extinctions that terminated the existence of so many other species of megafauna.  I believe they survived this extinction because unlike American species they had co-evolved with low populations of primitive humans for over a million years. This gave them time to evolve 3 adaptations that helped them survive alongside people for millennia: a) they learned to avoid people when possible, b) but females with cubs attack humans that they do come into close contact with, and c) they hibernate during severe winters when humans are more likely to take the risk of hunting a large dangerous animal because of desperation for food.  When hibernating they are out of sight and more difficult to find hidden away in dens.

The abundance of such a large iconic animal in California must have been reminiscent of many scenes that Paleo-Indians witnessed during the Pleistocene.  Most of California provided ideal habitat for grizzly bears, and they occurred everywhere in the state with the exception of the desert.  Grizzly bears like mostly open environments with some trees, while black bears ( Ursus americanus ) prefer mostly forested environments with some meadows.  Grizzly bears excluded black bears from the valleys, though their ranges overlapped in the more forested mountains.  Southern California valleys and the coastal region of northern California hosted grassy oak savannahs and brush oak chaparrals where grizzlies could feast on 4 foot tall clover and acorns that fell from over 5 different species of oak.  Along the coast they scavenged beached whales and other marine life.

Rose clover blooms in spring, Trifolium hirtum, Carlsbad, California

Large meadows of 4 foot tall rose clover (Trifolium hirtum) were an important food source for California grizzlies.

Blue oak savannah in California.  Grizzlies loved to forage for grass and acorns in this environment.

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Beached whales and other marine life were an important source of food for California grizzly bears.

Here is a passage from the below referenced book that gives an account of how common grizzly bears were during European colonization of the region.

“George Yount was among the first American pioneers in California, arriving in February, 1831.  Of grizzlies in the Napa Valley (where the town Yountville carries his name) he said ‘they were every where–upon the plains, in the valleys, and on the mountains…so that I have often killed as many as five or six in one day, and it was not unusual to see fifty of sixty within twenty-four hours.’ When Don Agustin Janssens rode between San Marcos and Santa Ynez in 1834 he said, ‘All the way we saw bears and it was winter and the acorns were dropping.’ John Bidwell, in the Sacramento Valley in 1841, saw sixteen in one drove and said that ‘grizzly bear were almost an hourly sight, in the vicinity of streams, and it was not uncommon to see thirty or forty a day.’  Even in Humboldt County, where much land is forested and unfavorable for the species, there is early mention of nine seen in one place, and again of ’40 bears in sight at once from a high point in the Mattole country,’ where a great extent of open land could be seen; all or most of these presumably were grizzlies, since black bears then were uncommon.”

One county of California-San Luis Obispo– was known as the “Valley of the Bears.”  Bear jerky from bears killed in this valley saved the first Spanish settlement in California at Monterey Bay when the settlers were in danger of starvation in 1770.

Grizzly populations temporarily increased in California from 1800-1860, thanks to the large Mexican ranches and their enormous herds of livestock.  Grizzlies directly hunted some and scavenged others that suffered natural deaths.  Grizzlies often lured curious cattle to them by lying on their backs with their paws waving in the air.  They pounced on cows venturing too close.  During droughts ranchers shot large numbers of cattle, horses, and sheep to prevent overgrazing, and grizzlies exploited this additional source of easy protein.  (Severe droughts strike California every decade.  These droughts are likely unrelated to anthropogenic global warming.)   The bears also foraged butchering grounds.

The Mexican ranchers didn’t always have good quality firearms, so they killed grizzlies with lassoes.  A group of men on horseback would lasso the bear and drag, strangle, or stress the animal to death.  It took great skill for both man and horse to lasso a grizzly, and it was very dangerous.  A grizzly might shake loose and charge.  In some cases a grizzly would seize the rope and pull the horse and rider toward it paw over paw.  If the rope was tied to the bridle, this could be disastrous for the horse and man.

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Rancheros lassoing a grizzly bear.  The early Spanish settlers in California often didn’t have good rifles, so they lassoed grizzlies, dragging or strangling them to death.  This took great skill but was extremely cruel.

Staged fights between bears and bulls were a popular “sport” in California during the 19th century.  Every major town had a bear-bull fight on every holiday.  The bear and bull were attached to each other with a 20 yard long leather strap, and they fought until 1 or both suffered fatal injuries.  The Mexican ranchers captured powerful large bears, so when Mexico owned California the bears usually won these cruel contests.  But when the U.S. gained control of the state, most of the bears supplied for these contests were small individuals captured in traps by miners, and the bulls usually won.  In 1 contest a bear was pitted against a cougar.  Surprisingly, the much smaller cat killed the bear.  A majority of Americans rejected this Spanish/Mexican custom, and local governments began passing ordinances against these spectacles, but they didn’t completely stop until grizzlies were extirpated here.

Between 1850-1890 the population of humans in California increased from 92,597 to 1,213,390.  This doomed California grizzlies.  Americans brought superior firearms capable of more efficient killing, and there were just too many conflicts between people and grizzlies.  The valleys where grizzlies thrived were also prime agricultural lands.  Farmers and ranchers would not tolerate grizzlies eating their crops and livestock.  City people did not want grizzlies busting into their homes to consume the contents of their cupboards.  Miners were afraid of getting mauled when they carried their pouches of gold dust to the nearest bar or brothel.  California grizzlies were ruthlessly hunted until about 1924 when there were none left in the state.

Reference:

Storer, Tracy and Lloyd Tevis

California Grizzly

University of California Press 1955

The Strange Little Star-nosed Mole (Condylura cristata)

December 2, 2016

Strange.  Cryptic.  Uncommon.  Unique.  These are all words that could be used to describe the star-nosed mole.  The alien-looking structure on the end of its nose is known as an Eimer’s organ.  All 30 species of moles have this organ, but none have one that is as developed as the star-nosed mole’s.  The Eimer’s organ is used to detect prey in underground darkness and water, but scientists aren’t sure how it works.  Some think it senses tacticle stimulation, while others believe it senses the electrical fields of prey. It may sense both.  In any case over half of a star-nosed mole’s brain is used to process information gathered by its Eimer’s organ.

The star-nosed mole is a semi-aquatic subterranean mammal, living in meadows and woods adjacent to streams, ponds, and marshes.  They also occasionally occur in drier habitats.  Their underground tunnels often lead to water.  Incredibly, they can smell underwater by blowing a bubble that sticks to the end of their nose.  They are the fastest feeder on the planet, able to detect and consume prey in .2 seconds.  Scientists believe they evolved this rapid feeding mechanism and well developed Eimer’s organ to help them survive wet muddy environments where there is a dense population of small insects.  Star-nosed moles feed upon insects, worms, mussels, snails, crustaceans, salamanders, frogs, and fish.

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Star-nosed mole.

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Range map for the star-nosed mole.  This map doesn’t include Richmond, County Georgia where I reside.  Star-nosed moles do occur in east central Georgia.  My cat killed a specimen and left it on my back porch about 10 years ago.  They likely have a more extensive range than this map indicates but are rare and haven’t been reported in many areas of their range.

As far as I know, I am the only person to report the presence of star-nosed moles in Richmond County, Georgia.  According to the scientific literature and accepted range maps, star-nosed moles don’t occur in east central Georgia.  But about 10 years ago, a cat killed a star-nosed mole in my back yard.  My lot is on a sandhill plateau approximately 1/2 mile from a creek and wetland.  All other cat-killed moles in my yard were the much more common eastern mole ( Scalopus aquaticus ).  There is no chance of misidentification–the star nose is obvious.

Star-nosed moles may have been more widespread in southeastern North America during cool Ice Ages.  Over half of their present day range was under glacial ice then, and their range shifted south.  Pleistocene-aged remains of star-nosed moles have been excavated from caves in Arkansas and Missouri–far outside their present day range.  Cool moist stages of climate with low evapotranspiration rates supported more boggy environments favored by star-nosed moles.  However, it’s possible star-nosed moles still occur in those states but exist in cryptic populations yet to be discovered (or recognized and reported) because it is an uncommon animal that lives underground and is not often seen.

Video about the star-nosed mole.

Reference:

Catania, Kenneth

“A Nose that Looks Like a Hand and Acts Like an Eye: the Unusual Mechanism of the Star-nosed Mole”

Journal of Comparative Physiology 85 (4) 1999

Pleistocene Manatees (Trichechus manatus)

November 28, 2016

Mammoths and mastodons no longer roam North America, but a relative of the elephants can still be found in Florida.  The manatee belongs to the superorder paenugulata which includes the proboscidea (elephants), the hyracoidea (hyraxes), and the sirenia (manatees and dugongs).  Strange as it may seem, these quite different looking animals are somewhat closely related.  Manatees share many anatomical characteristics with elephants.  Their incisors resemble elephant tusks, and the toenails on their flippers exactly match those found on elephant toes.  Manatees use their lips to feed on vegetation, much like elephants use their trunks when foraging for food.  And manatee teeth are replaced by horizontal forward movement– the same process of dental development that occurs in elephant mouths.  A scientist first recognized the anatomical similarities between manatees and elephants in 1945.  Recent genetic studies confirm this early cladistic analysis.

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The proboscidea, hyracoidea, and sirenia orders belong to the same clade–the paenugulata.

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All of these species of manatees are still extant except for Steller’s Sea Cow which was overhunted  to extinction in 1768.

The species of manatee still extant in Florida today ecologically replaced an extinct species of dugong during the late Pliocene or early Pleistocene.  This species is known as the West Indian manatee because it occurs along the Caribbean island coasts–also known as the West Indies.  Manatees occasionally swim as far north as Massachusetts during summer but return to waters off the coast of south Georgia and Florida before winter.  West Indian manatees can’t survive cold water temperature.  Fossil evidence shows manatees have long straggled north of their winter range–remains of manatees dating to the Pleistocene have been found near the coasts of South Carolina, Virginia, and New Jersey.  There is some evidence that manatees were extirpated from Florida during the coldest stage of the last Ice Age.  Fossils of manatees dating to before the Last Glacial Maximum in Florida resemble a subspecies no longer found in the state.  Manatees from the Caribbean recolonized Florida following the end of the last Ice Age.  Pleistocene-age manatee bones have been excavated from over 24 sites in Florida, and men hunted them as soon as Indians arrived in the region.

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Manatees in the St. Mary’s River, Georgia.  I saw manatees when I visited Wakulla Springs, Florida.

West Indian manatees feed upon over 60 kinds of aquatic plants such as eel grass and turtle grass, and they incidentally ingest snails and small fish while munching on vegetation.  The extinct Stellar’s sea cow ( Hydromalis gigas ) ate kelp.  Stellar’s sea cow was the largest species of manatee, formerly reaching lengths of 30 feet.  It was the only species of manatee adapted to live in cold water.  They evolved a layer of blubber to help them cope with the frigid temperatures of the north Pacific.  Sea cows were widespread during the Pleistocene, ranging as far south as Monterey Bay, California, but by 1747 when they were first discovered by Europeans, they were already relegated to a small relic population off Commander Island located in the remote Bering Sea.  They were overhunted to extinction by 1768.

Some archaeologists speculate Paleo-Indians first reached North America by following a route along the Pacific coast, but they have no concrete evidence.  The reduction in the population and range of Stellar’s sea cow may be indirect evidence supporting this hypothesis.  Prehistoric seafaring people likely overhunted Stellar’s sea cow and extirpated them over most of their former range.  Sea cows reproduced slowly and were easier to hunt than whales.  Kelp beds, the habitat they preferred, have remained abundant throughout their decline and extinction, so ecological change can’t be the reason they became extinct.

All extant species of manatees are in danger of extinction today precisely because of the slow reproductive rate that doomed Stellar’s sea cow.  Manatees reproduce fast enough to replace populations lost to cold snaps, red tides, and other causes of natural mortality, but the addition of deadly boat propellers to their environment may be pushing them over the edge.