Archive for the ‘Pleistocene Mammals’ Category

New Species of Late Pleistocene Ground Sloth and Peccary Discovered on Yucatan Peninsula

September 13, 2017

My ongoing mission to catalogue the faunal composition of piedmont Georgia as it was during the late Pleistocene is but an educated guess.  I base my guess on the lone fossil site in the region plus fossil sites located to the north, south, and west of the piedmont.  (See for my list: https://markgelbart.wordpress.com/2013/12/27/if-i-could-live-during-the-pleistocene-part-xii-my-mammal-checklist/ ) I think I know most of the mammal species that occurred here during the Pleistocene, but there were probably species living in the region I never would have guessed.  Even in regions with many Pleistocene-aged fossil sites, scientists are still discovering the presence of new species.  Within the last 5 years paleontologists identified giant short-faced bear (Arctodus simus) and collared peccary (Tayassu tajacu) specimens in Florida where these species were not formerly known.  The dhole (Cuon alpinus) crossed the Bering land bridge sometime during the Pleistocene, yet the only fossil specimens of this species in North America were found at 1 site in Mexico.  This means all the dholes that lived between Alaska and Mexico left zero fossil evidence, or at least none that has been found to date.  And now, just within the last 2 years, scientists have identified 2 new species of large mammals that lived on the Yucatan peninsula during the late Pleistocene.

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Map of the Quintana Roo province on the Yucatan Peninsula.  Evidence excavated from sinkhole caves indicates an unique fauna resided here during the late Pleistocene.

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Skull of Xibalbaonyx oviceps found in Yucatan sinkhole.

The Yucatan peninsula is dotted with numerous sinkholes and caves because rain water unevenly dissolves underlying limestone bedrock.  The sinkholes and caves preserve remains of animals for tens of thousands of years.  Cave divers have discovered the bones of gompotheres, glyptodonts, ground sloths, llamas, horses, tapirs, peccaries, spectacled bears, saber-tooths, bobcats, rabbits, fruit bats, and humans in these subterranean spaces.  (I’m aware of 4 mostly complete human skeletons found in Yucatan sinkholes and caves–1 dating to the incredibly early date of 14,350 calendar years BP.)  Bones of Shasta ground sloths and collared peccaries are among the specimens recovered here, but relatives of each, previously unknown to science, have recently been described in the scientific literature.  The new ground sloth species was identified from a specimen found in the Zapote sinkhole.  It was a mostly complete skeleton of a sub-adult that weighed at least 500 pounds when it was alive.  It is thought to have been adapted to a desert grassland environment.  Scientists gave it the unpronounceable scientific name–Xibalbaonyx oviceps.  It was closely related to Jefferson’s ground sloth (Megalonyx jeffersonii), a species that occurred all across North America from Florida to Alaska.  Perhaps X. oviceps was a desert offshoot of Jefferson’s ground sloth.  The new species of peccary was given the more pronounceable scientific name of Mucknalia minimas. I haven’t been able to obtain a copy of either paper describing the new species.  When I do I may write an addendum to this blog entry.

The presence of 2 species seemingly endemic to the Yucatan peninsula indicates the region was ecologically unique.  The area around the Hoyo del Negro fossil site (See: https://markgelbart.wordpress.com/2015/08/08/the-hoyo-negro-fossil-site-in-yucatan-mexico/ ) was a mix of tropical forest, thorny scrub, and wetland; but further inland desert grassland predominated.  I think small sinkhole lakes, like oases, probably existed in drier areas.

Who knows?  Maybe the piedmont region of southeastern North America hosted endemic large mammal species during the Pleistocene that are currently unknown to science.  Unfortunately, the lack of sites suitable for fossil preservation in the region could keep them cloaked in mystery for eternity.

On an unrelated note: While researching this blog entry, I learned about a llama specimen (the extinct  Hemiauchenia macrocephela) found in a Yucatan cave that was apparently butchered, cooked, and eaten by humans.  This information doesn’t seem to be generally known in the archaeological literature.

References:

Gonzalez, Arturo: et. al.

“The Arrival of Humans on the Yucatan Peninsula. Evidence from Submerged Caves in the State of Quintana Roo, Mexico”

Current Research in the Pleistocene January 2008

Stinnesbeck, S.; et. al.

“A New Fossil Peccary from the Pleistocene-Holocene Boundary of the Eastern Yucatan Peninsula, Mexico”

Journal of South American Earth Science 2016

Stinnesbeck, S. et. al.

“Xibalbaonyx oviceps, a New Megalonychid Ground Sloth (Folivora: Xenarthan) from the Late Pleistocene of the Yucatan Peninsula, Mexico and its Paleogeographic Significance”

Palz 91 June 2017

 

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How Far South did the Wolverine (Gulo gulo) Range during Ice Ages?

September 7, 2017

The voracious wolverine preys upon deer, caribou, and even moose when these much larger mammals flounder in deep snow.  The padded paws of the wolverine allow them to stay on top of the snow while the heavy hooved deer sink, making it easy for the wolverine to lock their jaws on a throat. The wolverine also preys on smaller animals and will eat insects and berries.  They live in remote wilderness areas, preferring high elevations with deep snow and plenty of tree or shrub cover.   Wolverines benefit from the presence of other large predators because they are just as much scavenger as predator.  During summer and fall wolverines are too clumsy to actively chase deer but will drive off much larger predators from their kills.  After they consume as much as they can eat, they spray musk on the remains, and it become unpalatable for other carnivores.  Wolverines store caches of dead meat during winter and are ideally suited to survive in cold unproductive natural communities.

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Historical range of the wolverine.  Camera traps suggest they have recently recolonized northern California. They also live in Eurasia.  During Ice Ages, wolverines probably ranged along the southern Appalachians perhaps as far south as north Georgia and Alabama.

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Male wolverines reach weights of 60 lbs but can drive away bears, cougars, and wolf packs. Wolverine cubs sometimes fall victim to the latter 2.

Wolverines occupy very large territories.  Males in Montana patrol 162 square miles on average, while male Yellowstone wolverines average a territory of an astounding 307 square miles.  Wolverines  live in low densities in boreal forests, and this makes their remains rare in the fossil record.  Nevertheless, subfossil remains of wolverines, dating to the Pleistocene, have been excavated from Maryland, Pennsylvania, Wyoming, Colorado, Nevada, Romania, Italy, Germany, France, and the United Kingdom.  (The wolverine is an Holarctic animal, living on both sides of the Arctic Circle.)  The specimen from Cumberland, Cave, Maryland is the southernmost known record of the wolverine in eastern North America and this is south of their known historical range during colonial times.  I hypothesize wolverines ranged into the southern Appalachians as far south as north Alabama and north Georgia during Ice Ages.  The key is deep snow–any climatic phase when deep snow regularly occurred at high elevations in the southern Appalachians would have been an invitation for wolverine range expansion south.  Other boreal species of mammals are found in the fossil record this far south including caribou, fisher, pine marten, porcupine, bog lemming, and red-backed vole.  Wolverine skeletal evidence is probably absent because they lived in low population densities at high elevations in forested environments where fossil preservation is rare.  Historical wolverine range is closely correlated with regions where snow stays on the ground through a good portion of spring.  Undoubtedly, spring snow cover existed in the southern Appalachians during the coldest stages of Ice Ages.

Most of the wolverine’s present day range was covered by glacial ice during Ice Ages, so it seems likely their range shifted south, like that of so many other species then.  How far south did this range shift?  We can only speculate.  But this is an animal that requires deep wilderness, and North America was nothing but deep wilderness before man.  Wolverines won’t cross clear-cuts or burned over land.  The main factor restricting wolverine range before man were the extensive grasslands that likely formed an ecological barrier to their expansion below the southern Appalachians.

References:

Hornocker, M; and H. Hash

“Ecology of the Wolverine in Northwestern Montana”

Canadian Journal of Zoology 59 (7) 1981

Inman, R.

“Wolverine Ecology and Conservation in the Western U.S.”

Swedish University Doctoral Thesis 2013

http://www.paleobiologydatabase.com

 

 

Pleistocene Saiga Antelopes

August 31, 2017

The saiga antelope (Saiga tatarica) ranged from western Europe to Alaska and the Yukon during some climate phases of the late Pleistocene.  This range closely corresponds with an environment known as the mammoth steppe.  This paleoenvironment was similar to the present day central Asian steppe but was more productive, hosting a greater variety of plants and microhabitats that included scrub, woodland, and wetland embedded in a sea of grass.  Summers were cool, winters were long, wind was constant, and precipitation was infrequent.  The bulbous nose of the saiga antelope is an adaptation for living in this kind of environment.  It helps warm frigid air and filter the dust in a dry windy climate.  The range of the saiga antelope has been greatly reduced since the late Pleistocene due to changes in the environment and overhunting by man.  Nevertheless, saiga antelope occurred in eastern Europe as late as the 17th century, indicating they are not a relict species confined to steppe grasslands.  A recent scientific study examining the bone chemistry of subfossil and extant saiga antelope specimens concluded this species can survive on a greater variety of plant foods than present day populations consume.

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Saiga antelopes are critically endangered today but lived from the British Isles to the Yukon, Canada during the late Pleistocene.

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Present day saiga antelope range.  During the Pleistocene they occurred from western Europe to Alaska.

This study found the diet of the saiga antelope overlapped with that of the caribou (Rangifer sp.) in southwestern Europe between 20,000 years BP-15,000 years BP.  It seems likely both species were subsisting upon lichen during winters when other plant foods were scarce.  Pleistocene saiga antelope apparently had a greater flexibility in their diet than present day populations.  The authors of this study suggest saiga antelope could potentially be introduced outside their present day range.  Poaching and disease outbreaks are endangering the surviving remnants of saiga antelope populations, so it could prove beneficial to establish new populations outside their present day range.  However, it’s possible some Pleistocene populations of saiga antelope may have been a distinct now extinct species with different dietary tolerances.  Some Russian paleontologist noted some morphological differences in saiga antelope specimens found outside their present day range, and they proposed a new species–Saiga borealis. Other paleontologists don’t accept this designation.  So far, no genetic studies have solved this difference of opinion.

The saiga antelope is considered a distant sister clade to the springbok-gerenuk clade.  They are the sole survivors of antelopes that roamed Europe before Ice Ages began to occur.  None of their closest relatives were able to evolve fast enough to survive deteriorating climatic conditions.

Reference:

Jurgensen, J.; at. al.

“Diet and Habitat of the Saiga Antelope during the Late Quaternary Using Stable Carbon and Nitrogene Isotope Ratios”

Quaternary Science Review March 2017

Extant South American Canids are Ancient Relics

August 16, 2017

Several species of medium-sized canids native to South America descend from species that formerly occupied North America.  The extant bush dog (Speothos vunaticus), maned wolf (Chrisocyon brachyuras), and the recently extinct Falkland Islands wolf (Dusicyon australis) are (or were) similar to primitive dogs that occurred across North America during the late Miocene and Pliocene.  The emergence of the Canis genus (wolves and coyotes) early during the Pleistocene competitively excluded these primitive dogs from North America, but their ancestors pushed through the jungles of Central America, and they colonized South America where they still thrive today when not persecuted by man. The tropical rain forests of Central America served as a geographical barrier that prevented Canis species from following their primitive relatives.  Though Canis species may be more adaptable overall, their primitive relatives were better able to withstand tropical conditions, a factor that saved them from extinction.

The South American bush dog is a widespread but uncommon pack-hunter that preys on large rodents, peccaries, and rheas.  One genetic study suggests they are most closely related to maned wolves, but another more recent genetic study determined they are most closely related to African hunting dogs.  A species similar to the African hunting dog lived in North America as late as the mid-Pleistocene, so the bush dog may very well be an offshoot of this canid line.  The maned wolf is a solitary species, not a pack-hunter–additional evidence supporting a closer evolutionary link between bush dogs and pack-hunting African dogs, rather than the maned wolf.  The bush dog was known from fossil evidence found in a Brazilian cave before it was recognized as an extant species.

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South American bush dogs.  They are descended from primitive dogs that roamed North America before the Canis genus dominated that continent.

The Falkland Islands wolf was the only mammal species native to the Falkland Islands.  It was a completely naïve species, unafraid of man, and was hunted to extinction by the late 19th century.  Settlers coveted its furry coat and were afraid it would kill their sheep.  Actually, the diet of this species is unknown, but it probably subsisted on penguins, geese, and sea shore scavenging.  How this species colonized the Falkland Islands, located 285 miles from the mainland of South America, was a mystery until recently.  Geologists discovered underwater ridges connected to the mainland that were above sea level during Ice Ages.  A narrow 20 mile straight between the ridges and the Falkland Islands froze into solid ice during winters of the Last Glacial Maximum (~16,000 years ago), allowing the canids to cross.  They may have been hunting penguins on the ice, leading them to the islands.  No other mammal found motivation to cross the ice bridge.

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Extinct Falkland Islands Wolf.  Unfortunately, they had no fear of people.

Genetic evidence suggests the Falkland Island and maned wolves are most closely related to false foxes (Lycalopex sp.), 6 species of which are found in South America today.  However, the Tibetan fox is the maned wolf’s closest living relative.  The Tibetan fox is likely related to the ancestors of all false foxes.  An extinct species of maned wolf (C. nearctus) lived in North America during the Pliocene.  Fossil evidence of this species has been found at sites in Arizona, California, and northern Mexico.  The maned wolf has long legs that help it look over tall grass for rodents–its main prey item.  Genetic evidence shows maned wolf populations increased during Ice Ages when grasslands expanded and contracted during interglacials.  Pliocene environments were often dry and included an expansion of prairie habitat, so it’s likely the North American maned wolf also had long legs.  The fossil evidence of C. nearctus is limited to lower jaws and teeth, so it’s not known how long its legs were.  Maned wolves are omnivorous, and they are important dispersers of seeds.  They often defecate on leafcutter ant nests, and the ants move the viable seeds, helping them germinate.

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Maned wolf.  Maned wolves lived in North America during the Pliocene.

The maned wolf grows to about 50 pounds, but a larger genus of primitive dogs lived in North America until the early Pleistocene.  Theriodictis hunted megafauna in Florida.  Species from the Canis genus outcompeted them in North America, but they continued to thrive in South America until the late Pleistocene extinctions of the megafauna.

Reference:

Nyakatura, K.; et. al.

“Updating the Evolutionary History of Carnivora (Mammalia): A New Species Level Super Tree Complete with Divergence Time Estimates”

BMC Biology 10 (12) 2017

Tedford, Richard; X. Wang, B. Taylor

“Phylogenetic Systematics of the North America Fossil Caninae”

Bulletin of the American Museum of Natural History 2009

 

The Enigmatic Small Wolf Species of the Early-Mid Pleistocene of North America

August 6, 2017

There were at least 5 species of wolf-sized canids living in North America from about ~1.8 million years BP-~300,000 years BP.  Edward’s wolf (Canis edwardii) was a medium-sized canid, averaging about 75 pounds, that apparently occurred from coast to coast.  It’s the same species formerly known as Canis priscolatrans, and it was an evolutionary dead end–its extinction occurred about 300,000 years ago.  Armbruster’s wolf (Canis armbrusteri) co-occurred with Edward’s wolf but was a larger species, weighing on average 125 pounds.  Armbruster’s wolf is thought to be the evolutionary ancestor of the famous dire wolf (Canis dirus) which became extinct about 11,000 years ago.  Troxell’s dog (Protocyon texanus) was related to African hunting dogs.  Fossil evidence of this species has been found in Texas, the Yukon, and Alaska; and it probably had a wider range than the fossil record indicates.  Perhaps it lived in low numbers in geographic regions where processes of preservation were rare. The timber wolf (Canis lupus) was apparently confined to Alaska and Eurasia during the mid-Pleistocene and didn’t colonize North America until the late Pleistocene.  Finally, a mystery species nearly identical to the present day coyote (Canis latrans) left fossil evidence at sites in Nebraska, Colorado, California, Arkansas, Pennsylvania, Maryland, and West Virginia.  Some of the fossils at these sites are estimated to be 1 million years old.  Paleontologists identified these specimens as Canis latrans, though they cautiously also referred to them as coyote-like.  However, a recent study of wolf, coyote, and dog genetics determined the coyote is a recently evolved species no older than 50,000 years when it first diverged from timber wolves.  This result suggests the mid-Pleistocene species identified as Canis latrans may be an extinct mystery species.

In addition to the fossil record scientists can use a molecular clock to determine when 2 or more species diverged from a common ancestor.  A species has a fixed mutation rate, and scientists add up generations of mutational changes to determine the time of divergence from its closest related species.  (This is a vastly oversimplified explanation but will suffice for the purpose of this blog article.)  There are problems with using molecular clocks.  Different species have different rates of mutation, and the mutation rate can change over time.  Scientists try to calibrate the molecular clock with the fossil record by using various statistical methods.  An early study of wolf and coyote genetics determined the 2 species diverged about 1 million years ago, and this result is consistent with the fossil record, but the results of the newer study mentioned above totally contradict the fossil evidence.  There are 2 explanations for this discrepancy.  a) The new study is wrong.  Maybe the scientists used too many assumptions and dodgy statistics and just came up with the wrong number.  or b) The new study is right, and the mid-Pleistocene species identified as Canis latrans was an evolutionary dead end that went extinct.  The similarity between this mystery species and Canis latrans is just a remarkable example of convergent evolution. c) The new study is right and is not inconsistent with the fossil record.  Perhaps the common ancestor of the coyote and timber wolf was coyote-like.  Ice Age glaciers caused the divergence.  Populations north of the Cordilleran ice sheet evolved into timber wolves but populations south of it remained coyote-like.

Below are images of mid-Pleistocene  skull and jaw specimens identified as Canis latrans along with the skull and jaw of a present day coyote.  I can’t tell the difference, so I favor explanation a.  Even in a case of convergent evolution, there would have to be some notable anatomical differences between 2 different species.

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Genetic evidence from 1 study suggests coyotes diverged from gray wolves about 50,000 years ago.  However, this skull, assigned to Canis latrans (coyote) from Maryland dates to >300,000 years ago.  Is the genetic evidence incorrect or was there a species then so similar to modern coyotes it deceived paleontologists? Image from the below referenced paper by Tedford et. al.

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Present day skulls of Canis latrans.

Some zoologists think coyotes and dogs should now be classified as subspecies of timber wolf based on the data from the newer genetics study.  I don’t agree.  The behavioral characteristics of wolves, dogs, and coyotes are too dissimilar; and they don’t normally interbreed in natural conditions.  Humans can easily eradicate wolves from a region, but they can not eliminate coyotes because the latter are so much better adapted for living close to people.  Wolves and coyotes can survive in the wilderness, but they make terrible pets.  Most dogs make excellent companions for people but can’t survive in the wild.  In my opinion wolves, coyotes, and dogs are closely related but definitely different species.

References:

Tedford, Richard; X. Wang, and B. Taylor

“Phylogenetic Systematics of the North American Fossil Caninae”

Bulletin of the American Museum of Natural History  2009

Von Holdt, Bridgett; et. al.

“Whole Genome Sequence Analysis Shows that Two Endemic Species of North American Wolf are Admixtures of Coyote and Gray Wolf”

Science Advances (27) July 2016

Wilson, Paul; et. al.

“DNA Profile of Eastern Canadian Wolf and Red Wolf Provide Evidence for a Common Evolutionary History Independent of the Gray Wolf”

Canadian Journal of Zoology 2000

 

 

 

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