Archive for the ‘Pleistocene Mammals’ Category

The Younger Dryas Cold Phase may have been Exacerbated by Megafauna Extinctions

July 26, 2017

In my previous blog entry I explained how Pleistocene megafaunal extinction impacted ecosystems, but some scientists hypothesize the loss of megafauna influenced atmospheric conditions as well.  The existence of enormous ice caps during Ice Ages caused extremely unstable climate conditions as the below temperature graphs illustrate.  The climate alternated between warm phases known as Dansgaard-Oeschger Events and cold phases referred to as Heinrich Events.  The onset of these patterns was often sudden occurring within decades, though some cold phases occurred gradually.  The fluctuations were interrelated.  Dansgaard-Oeschger Events melted glaciers and eventually released too much cold fresh water into oceans, shutting down ocean currents that carried tropically heated water to northern latitudes.  Colder oceans caused temperatures on adjacent continental land masses to drop. The Younger Dryas, a cold phase that began 12,900 years ago, was an exaggerated Heinrich Event.  Scientists, led by F. A. Smith, a professor at New Mexico University, propose the collapse of megafauna populations in North and South America contributed to the severity of the Younger Dryas stadial.

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Ice core data from Antarctica illustrates fluctuations in climate over the past 500,000 years.  The brief but severe Younger Dryas cold snap can’t be seen on this chart, but supposedly it was an anomaly compared to other fluctuations.

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Ice core data from Greenland showing fluctuations in climate over the past 23,000 years.  Within decades a warming climate phase reversed, and average annual temperatures matched the coldest of the preceding Ice Age.

Large populations of megafauna produce immense quantities of manure–a source of methane (CH4), an important greenhouse gas.  Megafaunal populations collapsed shortly before the Younger Dryas began, so perhaps without the mitigating effect of this manure-sourced methane temperatures dropped further than they would have, if these animals had still been present in the environment.  Moreover, more forest replaced grasslands because there were no megaherbivores suppressing tree regeneration.  Trees help reduce CO2, another greenhouse gas.  Today, methane produced by increasing populations of livestock combined with deforestation contribute to an increase in greenhouse gas concentration and global warming.

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Modern day livestock contribute to greenhouse gas emissions.  A new hypothesis suggests the extinction of Pleistocene megafauna in North and South America contributed to the severity of the Younger Dryas cold phase when average annual temperatures suddenly plummeted to levels not seen since the Last Glacial Maximum.

Reference:

Smith, F.A.; S. M. Elliott and S.K. Lyons

“Methane Emissions from Extinct Megafauna”

Nature Geoscience 3 (6) 2010

 

The Unraveling of Pleistocene Ecosystems in Southeastern North America

July 23, 2017

The entrance of humans into southeastern North America and the subsequent extinction of megafauna species had a profound effect on the region’s ecosystems.  Evidence from other regions suggests megafauna populations began to collapse during the Boling/Alerod interstadial, a warm phase of climate following the Glacial Maximum that lasted from ~15,000 years BP-~12,900 years BP.  Megafauna populations should have been increasing during this climate phase because the increase in precipitation and warmer temperatures fostered greater plant growth and species composition diversity.  However, the improved climatic conditions benefitted people and in turn the presence of humans is almost always disastrous for wildlife.  When the men failed on a day’s hunting trip, they still had plenty of food, thanks to the women who gathered wild plant foods and trapped fish, turtles, and birds in their nets all day.  The increased precipitation also caused an expansion of wetland habitat and aquatic resources. Under these environmental conditions human populations rose rapidly, much to the detriment of large animals.  Within a few thousand years humans wiped out almost all of the large mammal species in the south, so for the first time since a few million years after the KT impact that knocked off the dinosaurs, the region was nearly devoid of large megafauna populations.

Few scientists have studied the details of megafauna extinctions in the south and how they impacted the ecosystem.  One study (Smith, F.A. 2015 referenced below)  looked at all the Pleistocene sub-fossils found in Hall’s Cave, Texas–a site with well dated chronology and a continuous record of mammals from 22,000 years BP to the present.  A statistical analysis suggests many Pleistocene mammals were positively associated with other species.  This means complex interrelationships between species probably existed, though we have no way of knowing what they were.  This blog entry is my attempt, as an educated layman, to imagine what occurred as Pleistocene ecosystems unraveled.

I propose the first animals to be overhunted to extinction in the southeast were ground sloths, pampatheres, glyptodonts, and giant tortoises.  Ground sloths and pampatheres were important keystone species because they constructed extensive deep burrow systems.  (I also believe giant tortoises, like their extant relative the gopher tortoises, dug burrows.  Unfortunately, a paleontologist labeled giant tortoises as “non-burrowing” in a 1950’s era paper, and no qualified vertebrate zoologist has ever challenged his assumption.  I am unaware of any study of Hesperotestudo   anatomy that determined whether they could burrow or not.  If they couldn’t dig their own burrows, they must have been dependent upon ground sloth and pampathere burrows.) These burrow systems provided refuge, not only for ground sloths and pampatheres (a kind of giant armadillo) but many other species as well.  They served as shelter for hundreds of species of small vertebrates and invertebrates, much like the tunnels of prairie dogs and gopher tortoises do today.  I hypothesize ground sloths were immune to snake bite venom because their burrows likely served as winter dens for rattlensakes.  Large predators, bears, and peccaries probably used abandoned ground sloth burrows for shelter.  Ground sloths excavated large quantities of subsoil too and when mixed with topsoil these mounds supported unique plant communities.  It seems likely the plants that grew around ground sloth burrows were edible for ground sloths and many other herbivores.  I recently watched an episode of Expeditions with Patrick McMillan that showed a prairie dog town surrounded by mallow flowers.  Fossil coprolites indicate globe mallow was a favorite food of 1 species of ground sloth.

I doubt ground sloths lived in dense colonies like prairie dogs.  I guess there was normally 1 active ground sloth burrow every 3-5 square miles.  Intraspecific competition, if it existed in ground sloths, may have limited population density.  The burrows helped ground sloths survive climatic extremes, and the large powerful animals were able to hold their own against predators, but they were defenseless against men with projectile weapons.  They were the easiest of all the megafauna for men to kill–the most meat from the least effort–and therefore were the first to be hunted into extinction.  The increased frequency of fires set by humans may have also contributed to their extinction.  Instinct told them to take refuge in their burrows during lightning storms when the flashes of electricity ignited natural fires, but fires set by humans could overcome them at any time of year during sunny conditions.  Ground sloths could not outrun fires.  All the animals and plants that benefitted or completely depended upon ground sloths, pampatheres, and giant tortoises had to re-adapt to their absence.

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Photo of a prairie dog colony.  Though giant ground sloths and giant tortoises probably didn’t live in dense colonies, they also dug burrows throughout their range and were important keystone species that played as an important role in ecosystems as prairie dogs do today.  They were likely the first organisms to be wiped out by humans in North America.

The largest most dangerous predators were the next group of animals to be eliminated from the landscape.  Giant short-faced bears, giant lions, and fanged cats had no fear of people, yet they were no match for groups of men with projectile weapons.  Many of these animals were killed while contesting carcasses with people.  The decline of large carnivores likely occurred simultaneously with the extermination of mammoths and mastodons.  During the Boling/Alerod interstadial mastodon populations should have been increasing because this semi-aquatic species benefitted from the expansion of wetlands.  But humans drove mammoths and mastodons away from their favorite foraging grounds and watering holes, and they disrupted their migration routes.  The reproductive rates were too slow to keep up with human hunting pressure.

African elephants influence their environment today.  In Kruger National Park elephants uproot 1500 mature trees annually.  They convert forest into open savannah.  Mammoths and mastodons likely kept environments in southeastern North America in a constant state of flux.  The environment was patchy with various stages of forest succession located adjacent to other stages–meadow next to shrubby thickets alongside 2nd growth and mature woodland.  There were groves of large seeded fruits such as Osage orange, pawpaw, honey locust, and persimmon that had been planted in the excrement of the proboscideans.  After mammoths  and mastodons were eliminated the patchy woodland and grassland transformed into a monolithic mature forest that supported few large mammals.  The loss of patchy habitat hurt populations of llama, peccary, and tapir.  Even some small animals disappeared from the region, as their favored micro-environment converted to deep forest.

Next came the slaughter of horses and bison.  With mammoths and mastodons gone, the final populations of horses in southeastern North America were hemmed into smaller grasslands because forests expanded now that trees weren’t being uprooted with the same frequency.  This made them more vulnerable to human hunters.  Bison benefitted from their co-existence with horses.  Bison feed on the nutritious new growth spurred by horses grazing tall grass.  But the elimination of horses also meant bison, those that avoided human hunters, had a hard time surviving in the region.

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Pleistocene horses may have improved the quality of grazing for bison.

The loss of megafauna spelled the end of the line for a long list of commensal species including condors, and extinct species of vultures, eagles,  storks, and cowbirds.  There wasn’t enough prey for dire wolves and even extinct subspecies of jaguars and cougars.  Genetic evidence suggests all North American cougars descend from a population originating in South America 10,000 years ago.  Eventually, cougars recolonized the region, probably from a population that evolved a tendency to avoid man and prey on small game as well as deer.  And after European diseases decimated Indian populations, bison, and horses introduced by the Spanish recolonized the region as well.

References:

Malhi, Y. et. al.

“Megafauna and Ecosystem Function from the Pleistocene to the Anthropocene”

PNAS 113 (4) 2015

Smith, F.A. et. al.

“Unraveling the Consequences of the Terminal Pleistocene Megafauna Extinction on Mammal Community Assembly”

Ecography 39 2015

The Cookie Cutter Cat (Xenosmilus hodsonae)

June 13, 2017

Larry Martin is the paleontologist who invented the fanciful name of “cookie cutter cat” for this extinct species.  He proposed this big carnivore killed its prey by taking a bite and retreating, thereby removing a piece of flesh like a cookie cutter removes a section of dough.  Supposedly, the cat then waited around for its victim to die from the wound.  I don’t buy it.  It seems unlikely a predator would cease attacking a wounded animal.  Instead, I believe this powerfully built animal held its prey down with its sturdy forelimbs and bit through the throat.  I suspect this is how all species of fanged cats dispatched their prey.

The cookie cutter cat is a newly recognized species.  Though commercial fossil collectors discovered 2 nearly complete skeletons at the Haile fossil site in 1981, scientists didn’t identify it as a new species until 20 years later.  At first scientists assumed it was a scimitar-toothed cat (Dinobastis serus) based on skull and dentition.  There were 2 lines of fanged cats during the Pleistocene in North America–the scimitar-tooths or Homotheridae and the saber-tooths or Smilodontheridae.  Both belonged to the subfamily Machairodontinae.  Scimitar-tooths were previously known to be long-limbed and built for chasing down prey, while saber-tooths were robust and built for ambushing their victims.  However, paleontologists eventually realized the cookie cutter cat was an exception.  It was a scimitar-tooth cat built for ambushing its prey, like the saber-tooth line of cats.  Cookie cutter cats were robust and powerful and short-limbed.

Mounted skeleton of the extinct cookie cutter cat.  It was stout like a bear and about the size of a lion.

Fossils of cookie cutter cats have been found at 7 sites in Florida including Haile, Sarasota, Citrus County, Levy County, Santa Fe River, Hillsborough, and Marion County.  Specimens identified as belonging to the Xenosmilus genus  have also been found in Arizona and Uruguay.  Cookie cutter cats are known to have lived during the late Pliocene and early Pleistocene between 2.5 million years BP-1.5 million years BP.  The specimens at Haile were associated with many bones of peccaries, a likely prey item.

References:

Martin, Larry; and J. Babiarz, J, Hearst, and V. Naples

“Three Ways to be a Saber-tooth Cat”

The Science of Nature 87 (1) 2000

See also the University of Florida Museum web article.– https://www.floridamuseum.ufl.edu/florida-vertebrate-fossils/species/xenosmilus-hodsonae

 

 

 

 

 

 

Predator and Prey in the Early Pleistocene of Florida

June 8, 2017

Pleistocene ecosystems supported a great variety of large predators.  During the early Pleistocene the saber-toothed cat (Smilodon gracilis, ancestor of S. fatalis) and Edward’s wolf (Canis edwardii, possible ancestor of C. dirus) were 2 important carnivores that kept herbivore populations in check.  A study analyzed the chemistry of megafauna bones from 2 early Pleistocene-aged sites in Florida to determine what these 2 predators chose to prey upon.  The study included data from 110 specimens of 12 species excavated from Leisey Shell Pit, and 51 specimens of 9 species found at Inglis 1A.  Species used from Leisey Shell Pit in addition to the 2 carnivores mentioned above included mammoth, mastodon, gompothere, horse, 2 kinds of llama, 2 kinds of peccaries, white tail deer, and tapir.  Subfossil remains from this site date to between 1.5 million years BP-1.1 million years BP during an interglacial climate phase when the environment is thought to have been lowland forest and swamp, though there must have been some grassland.  Species used from Inglis 1A were mastodon, white-tail deer, peccary, tapir, horse, llama, and an extinct species of pronghorn along with Smilodon and Edward’s wolf.  Subfossil remains from Inglis 1A date to between 1.9 million years BP-1.6 million years BP during a glacial climate phase when the environment is thought to have been a mix of longleaf pine savannah, oak scrub, and forest.

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Jaw bone of the extinct Edward’s wolf, 1 of the oldest wolf species known to have lived in North America.

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Photoshopped Smilodon gracilis, the evolutionary ancestor of the late Pleistocene Smilodon fatalis.

The results of the study indicate Edward’s wolf ate a greater variety of prey than Smilodon, but both species were adaptable to changing environments.  During the interglacial period Smilodon ate herbivores that fed in forest environments (mastodon, deer, tapir, paleollama), while wolves mostly ate grassland herbivores (mammoth, horse).  However, during glacial periods when grasslands predominated Smilodon adapted by eating more grassland herbivores.  Choice of prey among individual saber-toothed cats varied.  Some individual cats ate nothing but forest herbivores, while others ate just grassland herbivores.  I think this shows saber-tooths were territorial animals that stayed in the same home range their entire life.  They ate whatever prey occurred within their established territory.  Herbivores that fed in both forest and grassland (large-headed llamas, gompotheres, peccaries) likely fell prey to both carnivores.

Reference:

Feranec, Robert; and L. Desantis

“Understanding Specifics in Generalist Diets of Carnivores by Analyzing Stable Carbon Isotope Values in Pleistocene Mammals of Florida”

Paleobiology 40 (3) 2014

Bearzilla’s Diet

June 4, 2017

WordPress has a feature that lets me see how many daily views my blog articles get.  For several years my article entitled “Bearzilla: the Biggest Bear Ever” is almost always the single highest viewed article of the day. https://markgelbart.wordpress.com/2012/12/10/bearzilla-the-biggest-bear-in-history/  The subject of that popular blog entry is Arctotherium angustidens, an extinct South American species of bear that reached estimated weights of 3500 pounds–the largest size of any bear known to science.  In that blog entry I also discuss the largest specimens of extant species of bears and include a photo I ripped off from google images of a 2100 pound polar bear.  I suspect that photo is what draws so many views.  I came across a fairly recent research paper in the Journal of Paleontology about A. angustidens with enough information for me to write an addendum to my original article.

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Illustration showing the early Pleistocene giant short-faced bear that lived in South America. It later evolved into a smaller more herbivorous species.

Scientists studied the pathology, morphology, chemical signatures, and biomechanics of A. angustidens bones to determine what this species ate.  Missing, broken, and worn teeth were common.  The evidence of these dental problems suggests the bears were damaging their teeth when they clumsily gnawed on bones.  Some bear teeth even had bone splinters lodged in them.  An individual young female bear had a tooth infection caused by a bone splinter in its tooth, and this was the probable cause of death.  These giant bears had large teeth cheek similar to the extant giant panda (Ailuropoda melanoleuca), but pandas don’t exhibit tooth damage on their diet of bamboo.  The frequent occurrence of tooth damage in Arctotherium can only be explained by a diet high in bone consumption.

An analysis of stable isotope ratios in Arctotherium bones does suggest this species included lots of meat in its diet, but it also ate plant material.  The scientists conclude Arctotherium was an omnivore.

When large bears first colonized South America they competed with just a few large carnivores such as saber-tooth cats.  There was an abundance of large slow-moving prey the bears could wrestle down.  Eventually, more species of predators colonized the continent, and some prey species evolved into faster runners.  Other prey species–the large ground sloths for example–may have evolved into stronger adversaries as well.  Bears that consumed more plant material had a better chance of surviving than those that competed with predators or failed to obtain prey.  This may be why Arctotherium’s descendants  evolved to eat more plants than meat.

Reference:

Soibelizon, Leopoldo; et. al.

“South American Giant Short-Faced Bear (Arctotherium angustidens) Diet: Evidence from Pathology, Morphology, Stable Isotopes, and Biomechanics”

Journal of Paleontology 88 (6) 2014

Striped Skunk (Mephitis mephitis) Dispersal During the Pleistocene

May 30, 2017

Most people don’t even think about where and when the various species of wildlife inhabiting their neighborhood originated. No matter how common a particular species may seem, it has not always been there.  The striped skunk is a generalist species that occurs all across the United States, and it is quite common in many regions, especially rural farm country. It is found in forests, fields, wilderness and suburbs.  They are an adaptable species, thanks to their omnivorous diet and unique defense strategy.  Yet, striped skunks have not always existed over their present day range.

The ancestors of all American skunk species came to this continent by crossing the Bering Land Bridge over 5 million years ago.  Paleontologists assign fossils of this ancestral species to the extinct  Martinogale genus.  About 2 million years ago striped skunks in the Mephitis genus diverged from spotted skunks in the Spilogale genus.  There is fossil evidence of early species of Mephitis skunks from the early and mid-Pleistocene in Nebraska, Colorado, and Florida.  However, this early species must have gone extinct over much of its range.  By 300,000 years ago, Mephitis skunks were restricted to what today is northern Mexico and southern Texas.  All present day striped skunks descend from this ancestral population, according to a study of striped skunk genetics.  Scientists studied genetic information from 314 specimens chosen from 20 states and determined striped skunks spread east and west from this population.  Early striped skunks, like their closest living relative–the hooded skunk (M. macroura), were probably well adapted to desert environments but evolved characteristics that helped them survive in woodlands and grasslands.  Over 250,000 years ago, striped skunks crossed the Mississippi River and colonized the entire southeast.  This probably occurred during a glacial stage when the river ran low and numerous sandbars facilitated the crossing.  The lower Mississippi River has served as a barrier, isolating populations of striped skunks ever since.

Geographic distribution striped skunk phylogroups based on 601 base pairs of cytochrome-b gene in mitochondrial DNA. Pie charts indicate the proportional representation of groups in each state. The hypothesized Pleistocene and Holocene dispersal patterns for striped skunk phylogroups are indicated by unique dash marks.

Dispersal of striped skunk population during the Pleistocene based on genetic evidence from 314 specimens taken from 20 states. Map from the below referenced study.

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The hooded skunk (Mephitis macroura) is the closest living relative of the striped skunk.  Its range is Mexico and the extreme southwestern U.S.  Genetic evidence suggests this is also the geographic range where striped skunks originated.

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Nice photo showing coat variation within the striped skunk population.  Striped skunks colonized southeastern North America about 300,000 years ago.  A primitive closely related species occupied this region before that.  It’s unclear when this predecessor became extinct.

~200,000 years ago striped skunks advanced up the Rocky Mountains from their southwestern refugium.  This population split into 2 clades on either side of the Great Basin 130,000 years ago.  This western population expanded east and colonized the Midwest.  Following the end of the last Ice Age, southeastern skunks colonized New England and expanded west, coming into contact with western populations in the Midwest.  This has resulted in an admixture of once genetically distinct populations.  The history of this dispersal explains why skunk physical characteristics vary so much. The upper Mississippi River is smaller than the lower part and is not an insurmountable barrier.  Admixtures occur along the upper part of the river.  Genetic studies of raccoons, deer mice, northern short-tailed shrews, 5-lined skinks, and leopard frogs show similar dispersal histories with the Mississippi River acting as a barrier isolating populations from each other.

Reference:

Barton, Heather; and Samantha Wisely

“Phylogeography of Striped Skunk (Mephitis mephitis) in North America: Pleistocene Dispersal and Contemporary Population Structure”

Journal of Mammalogy 93 (1) 2012

Horse Toe Bones and 14,000 Year Old Human Shit

May 22, 2017

The oldest known evidence of human presence in North America is some pieces of shit excavated from Paisley Cave, Oregon.  Carbon-dating of this feces indicates humans crapped in the cave about 14,350 calendar years ago.  The contents of these turds consists of bison, dog, bird, fish, grass, and sunflower seeds.  One study found the amount of cholesterol and phosphate in the crap points to an animal with a vegetarian rather than an omnivorous diet, and the authors of this paper don’t believe it is human manure.  They suggest the human DNA extracted from the specimens are a result of contamination from people mishandling it.  However, the contents were mostly animal matter, so I don’t understand how the naysayers who authored this paper can come to this conclusion.  Other scientists note the presence of wolf or fox DNA in the crap.  The scientists who are convinced the turds are human believe a wolf or fox pissed on the human shit after people left the latrine.  The turds contain human hair–perhaps the best evidence people were the shitters here.  Dried crap stuck to their ass crack hairs and the hair came off when they wiped with leaves.

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Horse toe bones were found in Paisley Cave along with 14,000 year old human feces.

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A 14,000 year old human turd found in Paisley Cave, Oregon.

Many vertebrate bones and human artifacts have been discovered in the cave.  (See: https://markgelbart.wordpress.com/2010/10/29/the-paisley-cave-pre-clovis-site/ ).  Paleontologists studied the horse toe bones excavated near the human feces because they wanted to determine which species of horse co-existed with humans in this region then.  They believe with a >99% probability the toe bones belonged to an extinct species known as the Mexican horse (Equus conversidens). Most fossil material of this species has been found in Mexico, hence the name, but it likely occurred all across North America.  The Mexican horse was stocky and stilt-legged.

Paleontologists disagree over the number of horse species that lived in North America during the late Pleistocene.  Some believe there were 2 species, while others think there were more than 14 species.  Genetic evidence supports the proposed smaller number of species.

I have no doubt humans were responsible for the extinction of North American horses through overhunting and disruption of ecosystems.  When Europeans re-introduced horses to North America during the 16th century, horses went wild and thrived everywhere on the continent.  It seems unlikely an environmental change capable of causing horse extinctions occurred for such a short interval some time between 10,000 BP and 1500 AD.  Horses eat grass and coarse vegetation–plant material that never became scarce during any climate phase or change.  Climate change models of extinction don’t work at all for such an adaptable and widespread animal as the horse.

I remember when I first started studying the debate over megafauna extinction.  Opposition to human overkill as a cause of extinction centered around the flimsy argument that there was a lack of archaeological evidence of humans hunting horses in North America.  Since then, irrefutable proof humans hunted horses here has been unearthed at several sites.  Wally’s Beach in Alberta, Canada was the first site where archaeologists agreed evidence humans hunted horses was unmistakable. Bluefish Cave in the Yukon is located north of the former Cordilleran Ice Sheet.  Evidence humans hunted and ate Ice Age horses has also been discovered in this cave, and it dates to as early as 24,000 years ago.  Humans carried horse, caribou, elk, dall sheep, bison, and bird into the cave.  36,000 mammal bones have been excavated from this site.  Wolves, lions, and foxes, in addition to people are responsible for the bone accumulation.  And now, South American archaeologists believe a cave in Argentina holds evidence of human exploitation of horse.  Stone tools are found in association with human-modified bones of horse, hippidion (an exclusively South American species of horse), llama, toxodon, giant armadillo (Eutatus) and ground sloth (Megatherium and Glossotherium).

The evidence humans did hunt megafauna is mounting but will probably never convince old school archaeologists who (I believe) stubbornly refuse to admit they were wrong for so many years.

References:

Bourgeon, L.; A. Burta, T. Higgins

“Earliest Human Presence in North America Dated to the Last Glacial Maximum: New Radio-carbon dates from Bluefish Cave, Yukon”

Plos One January 2017

McHorse, Brianna; Edward Davis, Eric Scott, Dennis Jenkins

“What Species of Horse was Coeval with North America’s Earliest Humans in the Paisley Caves?”

Journal of Vertebrate Paleontology September 2016

Politis, Gustavo; M. Gutierrez, D. Rafus

“The Arrival of Homo Sapiens into the Southern Cone at 14,000 Years Ago”

Plos One September 2016

Sistiaga, A.; F. Berna, R. Laursen, P. Goldberg

“Steroidal Biomarker Analysis of a 14,000 Year Old Putative Human Coprolite from Paisley Cave”

Journal of Archaeological Science 2014

 

First Bone-eating Dog (Borophagus sp.) Tooth Found in South Carolina

May 17, 2017

The Borophagine dogs were an incredibly successful lineage of carnivores that lived from ~34 million years BP to ~2 million years BP and perhaps beyond.  They ranged throughout North America from coast to coast and from Canada to Honduras.  16 species of Borophagine dogs are known from 12 different fossil sites in Florida alone, and in the rest of the southeast specimens have also been found in North Carolina and Maryland.  Recently, an amateur fossil collector found 1 pre-molar of a Borophagus in a spoil pile at the Martin-Marietta Orangeburg Quarry located in Orangeburg County, South Carolina.  This animal was probably common in South Carolina for millions of years, but this is the only known evidence it ever existed in the state.  Paleontologists examined the tooth and determined it compared favorably to a pre-molar of Borophagus hilli, a species that reached a weight of 130 pounds.  The age of this fossil is estimated to be between 3.9 million years BP-3.1 million years BP based on associated microfossils.  B. hilli co-occurred with another species of Borophagine dog–B. diversidensThey must have occupied different ecological niches, maybe like modern day wolves and coyotes.

Jaw bone of Borophagus hilli–the Pliocene bone-eating dog.

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Artist’s depiction of the extinct bone-eating dog.  They had bulging foreheads.  Their teeth and jaws were similar to those of the extant spotted hyena–an example of convergent evolution.

Early species of Borophagine dogs were omnivorous.  Epicyon haydenii was the largest known species of canid in history, reaching weights of over 500 pounds.  This species lived between 12 million years BP-6 million years BP, and it probably occupied a bear-like ecological niche.  Borophagine dogs later evolved into more carnivorous forms, resembling modern day spotted hyenas (Crocuta crocuta) in build and dentition, hence the reason they’re often called bone-eating dogs.

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Epicyon haydenii was the largest known canid in history, growing as large as a grizzly bear.  They were more omnivorous than their later descendants.  They lived during the Miocene.

Borophagus sp.

Scan of the lower 4th pre-molar of a Borophagus.  This is the only fossil evidence found in South Carolina of a species that was formerly common in the region for millions of years.

Despite their long reign as an important carnivore in the American ecosystem, Borophagine dogs became extinct during the late Pliocene or early Pleistocene.  The last species of Borophagine dogs co-existed with dogs belonging to the Canidae family for millions of years.  The Canidae were newcomers from Eurasia that crossed the Bering land bridge to reach North America.  Species from the Canidae family were better able to adapt to changes in the environment during the early Pleistocene and likely outcompeted Borophagine dogs, contributing to their extinction and completely replacing them ecologically.

Reference:

Tseng, Z. Jack; and Jonathan Geisler

“The First Fossil Record of Borophagine Dogs (Mammalia: Carnivora) from South Carolina USA”

Journal of Vertebrate Paleontology 36 (2) March 2016

Dumpster Dingoes

May 9, 2017

Bacteria. Cockroaches. Flies. And even higher organisms. Mice. Rats. Sea gulls. Crows. Bald Eagles. Cats. Dogs. Wolves. Bears.  These are just some of the organisms that benefit from the food waste produced by humans.  We waste up to 40% of the food we produce.  The proliferation of Homo sapiens since the late Pleistocene has been detrimental to many species, but others have adapted to our presence.  Scientists estimate anthropogenic sources, including livestock and garbage, make up 32% of the worldwide gray wolf diet.  The last surviving population of Asiatic lions almost entirely subsists on livestock.  Studies show Australian dingoes and red foxes that live near landfills have smaller home ranges and higher survival rates than other individuals of the same species.  Dingoes living near garbage dumps grow fat and mate with domestic dogs, producing hybrids that could be called dumpster dingoes.  This same study found black bears foraging around dumpsters have shorter lifespans because they come into conflict with people and get shot.

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Landfills are excellent sites for bird watching.  They attract gulls, crows, and vultures.  I have even seen a bald eagle soaring over one.

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Dogs evolved from wolves that hung around human refuse heaps.

Dingoes are super efficient hunters that prey on almost everything they can kill

Dingo chasing a kangaroo.  Dingoes that hang around landfills get fat and lazy and mate with domestic dogs.

The existence of human refuse heaps likely spurred the evolution of wolf into dog.  The physical characteristics that differentiate dogs from wolves share the same genetic pathway with tameness.  The 2nd and 3rd generations of canids with the least flight response develop the floppy ears and multi-colored coats common in domestic dogs.  Some scientists think it possible some modern day wolves scavenging dumpsters could again evolve into a type of dog.

Genetic studies suggest dogs developed the ability to digest more starch about 4000-7000 years ago–another step in the ongoing evolution of wolf to dog.  This coincides with the development of agriculture when humans began cultivating cereal grains.  Dogs with digestive systems capable of producing more amylase, the enzyme that helps convert starch to sugar, were better able to survive on bread when humans started consuming more cereal grains instead of (or as a supplement to)  meat.

Dingoes descend from dogs brought to Australia about 4000 years ago by people from the subcontinent of India who later assimilated with Australian aborigines.  Dingoes are primitive dogs similar enough to their wolf ancestors that they can revert to the wild and thrive.  Dingoes rapidly became the top non-human predator in Australia.  Most people are unaware dingoes live in America as well. ( See: https://markgelbart.wordpress.com/2013/02/11/the-american-dingo/ ) Native Americans brought primitive dogs with them from Asia, and some of them went wild here just like they did in Australia.  North American dingoes are known as Carolina dogs and were not recognized as a distinct wild canid until a scientist found them running wild during the 1970s on the Savannah River Site in South Carolina.

The observed differences between wolf, dingo, and dog are a good example of recent evolution.  They also show the line between species can be blurry.  All 3 can interbreed and produce fertile offspring.  So some scientists think dogs and dingoes should be classified as subspecies of wolf.  On the other hand the physical and behavioral characteristics of each are quite different, and some scientists still classify them as distinct species.  Domestic dogs are entirely dependent upon humans, dingoes (a transitional form between dog and wolf) can take us or leave us, and wolves avoid us and probably wish humans would become extinct.  I prefer classifying them as separate species based on behavioral differences.

References:

Marshall-Pescini, Sarah; Ingo Besserdick, C. Kratz, F. Rang

“Exploring Differences in Dogs and Wolves’ Preference for Risk in Foraging Trash”

Frontiers in Psychology August 2016

Newsome, Thomas; Gary Ballard, Matthew Crouther, and Chris Dickman

“Dietary Niche Overlap of Free-Roaming Dingoes and Domestic Dogs: The Role of Human-Provided Food”

Journal of Mammalogy April 2014

Oro, Daniel; et. al.

“Ecological and Evolutionary Implications of Food Subsidies from Humans”

Ecology Letters October 2013

 

 

The Pleistocene Great Smoky Mountains

April 23, 2017

I renewed my subscription to the Southeastern Naturalist, so I could read a recent monograph that inventoried the mammal fauna of the Great Smoky Mountains National Park.  According to this paper, 68 species of mammals have been documented in the park, and 1 scientist predicts an additional 4 species might eventually be found there.  I suspect this number is greatly exaggerated–many of the species are small animals not documented in the park since the initial survey when the park was established in the 1930’s.  Those species not documented recently could very well be extirpated from the park.  The flora of the Great Smoky Mountains National Park is impressive but don’t plan a trip and expect to see much wildlife.  I visited the park once and saw just 1 squirrel and no other mammals besides lots of people.  There are 24 species of insectivores and bats allegedly inhabiting the park.  These species are difficult to see and enjoy.  That leaves 44 species and of these only 5 are considered megafauna (animals weighing over 40 pounds). The “big 5” are white tailed deer, elk, black bear, wild boar, and coyote.  The latter 2 are considered invasive, but I think of the coyote as a native species that is recolonizing former territory occupied during the Pleistocene.

There are probably more white tailed deer outside the park in the surrounding farmland.  White tailed deer prefer forest edge habitat, and most of the park has succeeded to old growth.  Elk were re-introduced here in 2001, but they inhabit a small area of the park difficult to access.  The road leading to this spot is a dangerous single lane dirt path on the side of a mountain.  Supposedly, the black bear population in the park is about 1600.  During the summer black cherries (Prunus serotina) make up 25% of the bear’s diet.  Garbage provides 8% of their diet here.  The author of the below referenced monograph claims to have several photographs of cougars taken by park visitors circa 2003.  These may be of captive cougars released by owners who no longer wanted to care for them.  Cougars are normally secretive, and semi-tame cats may have been easier to photograph.  I doubt there is a breeding population of cougars in the park, but I wouldn’t rule it out, and they may eventually recolonize the region, if they keep expanding their range from the west and south Florida.

Image result for map of Great Smoky Mountains national park

Location of the Great Smoky Mountains Park.  The diversity of megafauna species in this park is much lower now than it was in this region during the Pleistocene.

Image result for black bear eating cherries

Strange as it may seem, wild black cherries make up to 25% of the black bear’s diet during mid to late summer in the Great Smoky Mountains National Park.

Image result for striped skunks in the Great Smoky Mountains National Park

The below referenced monograph reports a population of 30 striped skunks inhabit the Cades Cove Campground of the Great Smoky Mountains National Park.  They den in drainage culverts.  Avoid them or you will endure a stinky vacation.

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A fluctuating population of endangered Indiana bats roosts in a cave in Cades Cove.  Bats can be seen at dusk.

The variety and abundance of megafauna in the Great Smoky Mountains National Park is disappointing, but it was spectacular during the Pleistocene.  The natural communities then were similar to those of today, but during cold glacials there probably were more spruce trees and grassy balds and in higher elevations there may have even been tundra-like environments.  Here’s a list of large mammals (based on fossil evidence) that definitely inhabited the park region until ~11,000 BP or beyond.

Jefferson’s ground sloth

Harlan’s ground sloth

tapir

horse

half-ass

mastodon

long-nosed peccary

flat-headed peccary

stout-legged llama

helmeted musk-ox

bison

white-tailed deer

caribou

elk (probably not until 15,000 years BP)

giant beaver

black bear

Florida spectacled bear

giant short-faced bear

cougar

jaguar

saber-toothed cat

scimitar-toothed cat

coyote

dire wolf

Here’s a list of additional megafauna species that likely inhabited the park but whose nearest fossil remains are a considerable distance away.

pampathere

stag-moose

Columbian mammoth

woolly mammoth

Columbian mammoth x woolly mammoth hybrids

gompothere (during warm climate cycles)

giant lion

dhole

The Pleistocene Great Smoky Mountains hosted ~31 megafauna species compared to the present day total of 5.  This is a >80% reduction.  How sad.

Reference:

Linzey, Donald

“Mammals of the Great Smoky Mountains National Park: 2016 Revision”

Southeastern Naturalist 15 Monograph (8) 2016