Archive for the ‘Pleistocene Mammals’ Category

Speculative Distributions of Megafauna in Georgia 36,000 years BP

April 15, 2018

A recent statistical study estimated the abundance and natural ranges of megafauna species (mammals over 40 pounds), if man didn’t exist today.  They analyzed 5,742 megafauna species that have existed over the past 130,000 years, a time span including a full glacial/interglacial cycle.  Not surprisingly, they concluded the natural ranges and abundance of megafauna would be much greater today, if not for man.

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Maps showing natural ranges and abundance of megafauna.  The top shows today’s abundance.  The bottom shows abundance today, if man didn’t exist.  Map is from the below reference.

This study inspired me to draw speculative range maps for selected megafauna species that lived in Georgia 36,000 years ago–long before people ruined the wilderness.  I chose this time period because it was an interstadial, a warmer wetter climate phase within the last Ice Age, and I think wildlife populations were higher then than during the Full Glacial Maximum when at least some of Georgia consisted of desert-like habitat.  My maps are educated guesses because the Pleistocene fossil record of Georgia is extremely incomplete.  Megafauna populations were not evenly distributed throughout the state.  I assumed the northern part of the state held more forest and woodland, while the southern half hosted more grassland.  But both environments existed in most of the state, often side-by-side.  Therefore, forest and forest edge species such as tapirs and long-nosed peccaries were more abundant in the northern part of the state.  Bison and horse were more numerous on the coastal plain.  Some animals migrated in and out of the state.  Isotopic evidence suggest mastodons moved back and forth between Florida and Georgia.  Like leaders of today’s elephant herds, experienced matriarchs knew where rich sources of food and mineral licks were located.  Some herds of mammoths probably moved great distances as well.  Flat-headed peccaries likely favored the sand hill scrub habitat along the fall line.

Evidence of caribou in north Georgia dates to the Last Glacial Maximum, but I believe they were so abundant even during interstadials that some herds wandered as far south as Georgia.  There is no fossil evidence of helmeted musk-ox, stag-moose, giant lion, or saber-tooth in Georgia.  I’m certain giant lion and saber-tooth did range into Georgia, and it seems probable helmeted musk-ox and stag-moose did as well.  Fossil evidence of giant lions has been found in Florida and Mississippi.  Saber-tooth bones have been recovered from all the states surrounding Georgia.  Fossil remains of stag-moose and helmeted musk-ox have been excavated from sites on the same latitude as Georgia.

The dots on my maps don’t represent any specific numerical value, but the bigger ones indicate larger populations. The maps include the 10,000 square miles of continental shelf that was above sea level between ~83,000 years BP-~7800 years BP.

Range maps of selected megafauna species in Georgia 36,000 years ago.  Click to enlarge.  I know the labels on the maps are hard to see so from left to right on the top row they are mastodon, mammoth, Jefferson’s ground sloth, stag-moose, stout-legged llama, large-headed llama.  Middle row from left to right: long-horned bison, horse, long-nosed peccary, helmeted musk-ox, giant beaver, saber-tooth.  Bottom row from left to right: tapir, caribou, flat-headed peccary, giant lion, jaguar, dire wolf.

Reference:

Faurby, S; and J.C. Svenning

“Historic and Pre-Historic Human-Driven Extinctions have Reshaped Global Mammal Diversity Patterns”

Diversity and Distribution 21 (10) Augusts 2015

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The Late Pleistocene Extinction of Leopards (Panthera pardus) from Sumatra

March 8, 2018

During temperate climate cycles of the Pleistocene leopards enjoyed an even wider geographic range than they do today, living in Europe as well as Africa and Asia.  Leopards colonized the island of Sumatra during the middle Pleistocene but became extinct there at the end of the Pleistocene, despite continuing to thrive elsewhere in Asia.  Scientists used a statistical model to determine why leopards disappeared from Sumatra.  They considered all potential competing carnivores and total prey biomass in their calculations.   Leopards shared Sumatra with orangutans, monkeys, humans, elephants, deer, tapir, pigs, sun bears, tigers, clouded leopard, Asian golden cats, and dholes.  Tigers are known to depress leopard populations in regions where the 2 species overlap; and dholes, a pack-hunting dog, compete for the same large prey species.  Scientists expected the model to show competition with tigers and dholes caused the extinction of leopards on Sumatra.  However, when they removed the influence of these 2 species from their model, leopards still became extinct.  Leopards also became extinct when humans were removed from the simulation.  Surprisingly, the statistical simulation suggests competition with clouded leopards (Neofelis diardi) and Asian golden cats (Pardofelis temminckii) caused the extinction of leopards on Sumatra.

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Location of Sumatra.

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Asian golden cats.  This species along with clouded leopards outcompeted leopards on Sumatra following the end of the Pleistocene.

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Clouded leopard.

The authors of this study propose ecological changes following the end of the Pleistocene greatly favored smaller forest cats over leopards.  During Ice Ages Sumatra was a mix of savannah, woodland, and forest; but wetter climate fostered the spread of thick forest.  Larger prey species became less common, so leopards were forced to compete with the smaller cats for smaller prey items.  Both of the smaller species of cats reproduce faster than leopards and produce larger litter sizes.  The extremely adaptable leopard was actually squeezed out of its ecological niche on Sumatra by 2 smaller felines.

Adult leopards weight between 80-200 pounds compared to a maximum of 57 pounds for clouded leopards and 35 pounds for Asian golden cats.  The latter 2 species are efficient predators of small animals and need less food than leopards, giving them an advantage when available protein biomass declines.

Clouded leopards are 1 of the most primitive species of living cats and may be related to the evolutionary link between big and small cats.  The Sunda clouded leopard is the species that lives on Sumatra.  It diverged from the other species of clouded leopard ((Neofelis nebulosa) about 70,000 years ago.  Clouded leopards from Borneo crossed a now submerged land bridge and colonized Sumatra following the Tuba volcanic eruption that wiped out much of Sumatra’s wildlife ~70,000 years BP. The Sunda clouded leopard was not recognized as a separate species until 2006.

Reference:

Volmer, R.; et. al.

“Did Panthera pardus (Linneaus 1758) become Extinct in Sumatra because of Competition for Prey?  Modeling Interspecific Competition within the Late Pleistocene Carnivore Guild of the Paday Highlands, Sumatra”

Paleogeography, Paleoclimatology, and Paleoecology 2018

More Evidence against the Climate Change Model of Late Pleistocene Extinctions

March 4, 2018

Many extinct species of Pleistocene megafauna had a wide ranging geographic distribution.  Jefferson’s ground sloth, long-nosed peccary, Columbian mammoth, and mastodon occurred from coast to coast and from Florida to the glacial boundary.  These species and their similar evolutionary ancestors existed across the continent for millions of years, surviving dozens of major and minor climatic fluctuations.  They lived in a variety of environments and were capable of subsisting on many different foods.  Multiple lines of evidence show these pre-historic beasts ate a varied diet.  Mastodon coprolites (subfossil feces) contain bald cypress, buttonbush, spruce twigs, fruit, acorns, aquatic plants, and numerous other items.  Now, a new study of mastodon teeth using dental microwear texture analysis confirms that mastodons ate a wide variety of foods.

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Mastodon tooth.  Scientists looked at mastodon teeth using microscope technology and determined mastodons from different regions ate different foods.

Scientists microscopically examined 65 mastodon teeth that were found in 4 different geographic locations including Florida, Missouri, Indiana, and New York.  The microwear found on mastodon teeth from Florida differed from wear on teeth from northern mastodons.  Florida mastodons primarily ate bald cypress twigs, while northern mastodons ate spruce, hemlock, pine, larch, and juniper.  The differences in tooth wear indicate mastodons could eat a variety of plant foods and were not dependent upon a single species.  The authors of this study also looked at mastodon teeth from different climatic stages in Missouri.  Mastodon teeth from a climate stage when open jack pine and prairie predominated showed little difference from teeth dated to a climate stage when spruce dominated the landscape.  The microwear on mastodon teeth resembles the microwear found on 2 living species–moose and black rhino.  Like mastodon, these 2 species subsist on woody browse.

I think this study is just more evidence against the climate change model of extinction that proposes changes in climate caused corresponding changes in plant composition, leading to megafaunal extinctions through nutritional deficit starvation.  None of the plants mastodons ate ever disappeared or even became rare in the environment. The authors of this study take a more neutral stance toward the debate.  They acknowledge the “plasticity” of mastodon diet but seem reluctant to admit their study is strong evidence against the climate change model of extinction.  Instead, they suggest future studies using dental microwear texture analysis could uncover the reason why megafauna became extinct.  In my opinion it already has.  Their data rules out the climate change model of extinction by revealing the dietary adaptability of mastodons.  Through the process of elimination, human overkill is the only plausible cause left standing.

Reference:

Green, J.; Larisa DeSantis and G. Smith

“Regional Variation in the Browsing Diet of Pleistocene Mammut americanum (Mammalia, Proboscidea) as Recorded by Dental Microwear Texture Analysis”

Paleogeography, Paleoclimatology, and Paleoecology August 2017

The Galerian Migration hypothesis

February 25, 2018

During the middle Pleistocene the faunal diversity of Europe increased.  Scientists attribute this to glacial/interglacial transitions that changed the environment, transforming it from forest to grassland and savannah.  Forests were restricted to narrow corridors along rivers and upper elevations.  Cooling temperatures and aridity caused these changes.  Animals from Africa and Asia colonized the open savannahs that became established along the Danube and Po River valleys.  Red deer, atlas deer, wild boar, bison, aurochs, an extinct species of Indian water buffalo (Hemibos galerianus), and horses invaded from Asia.  An extinct species of temperate-adapted elephant (Elephas antiquus), mammoth (Mammuthus trogontherii), rhino, lion,  leopard, spotted hyena, and Homo erectus came from Africa.  The Galerian Migration Hypothesis posits archaic humans first colonized Europe during this time period because they were a part of this savannah ecosystem, and they used the same route as their contemporaries in the animal world.

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Map of the Danube River.  The Po River goes through northern Italy.  The Galerian Migration Hypothesis proposes archaic humans first entered Europe through savannahs in these 2 river valleys.

Data from magnetstratigraphy supports the Galerian Migration Hypothesis.  Scientists can date objects based on which direction the magnetic minerals within associated rocks are oriented.  The earth’s polarity has shifted periodically throughout history, causing magnetic minerals in rocks to point in certain directions.  Scientists calibrate changes in polarity with radiometric dating, so magnetstratigraphy provides useful parameters.  Scientists know from magnetstratigraphy that Homo erectus probably first colonized Europe between 780,000 years BP-990,000 years BP. The oldest  Homo erectus fossil known from Europe falls within these dates. These dates correspond well with environmental changes, and changes in faunal composition.  Homo erectus originated in Africa and colonized Asia and the Middle East as early as 1.9 million years ago, but there was a delay before they reached Europe.

The invasion of humans and spotted hyenas likely drove the extinction of hyena species already in Europe–Pachycrocuta breverosti and Pliocrocuta perra.  The newcomers outcompeted the native hyenas for the narrow hunter/scavenger niche.

During full glacial maximums southern Italy and Spain served as refuges for species such as Elephas antiquus and a temperate-adapted species of rhino.  However, during the Last Glacial Maximum, the superior hunting humans (Homo sapiens) probably overhunted these species to extinction in their glacial refugia.

Reference:

Muttoni G.; Giancarlo Scardio, and Dennis Kane

“Early Hominins in Europe: The Galerian Migration Hypothesis”

Quaternary Science Review 180 Jan 2018

Scientists Recognize New Species of Late Pleistocene Horse (Haringtonhippus francisi)

January 29, 2018

Scientists recently recognized a new species and genera of extinct Pleistocene horse from fossil specimens already in museums.  Some of these specimens were collected over 100 years ago and were wrongly assumed to represent previously known species or genera.  During the Pleistocene there were 3 lineages of horses in the Americas–the caballine horses, the New World stilt-legged horses, and the hippidion horses.  The caballine horses belong to the Equus genus which includes all living species of horses, donkeys, and zebras.  The species of caballine horses that lived in North and South America likely included the predecessor of the modern day domesticated horse.  It was probably the same species.  The New World stilt-legged horses so anatomically resembled Asiatic wild asses and donkeys that paleontologists mistakenly thought they were closely related.  In recent years paleontologists began to reject this assumed affinity, and the genetic study cited in this blog entry supports their re-assessment.  The hippidion horses were robust species restricted to South America.  A new genetic study determined the New World stilt-legged horses, previously classified as belonging to the equus genus, were different enough to deserve their own genus.  Scientists gave this species the scientific name Haringtonhippus francisi. The species was named after the renowned Canadian paleontologist, Richard Harington.  The type specimen anatomically described in the paper was originally discovered in Wharton County, Texas.

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Artists’s representation of Haringtonhippus francisi.  The coat color is the artist’s fanciful guess.

The genetic evidence suggests haringtonhippus  horses diverged from equus horses between 4-5 million years ago.  The hippidion horses diverged from the equus/haringtonhippus genera between 5-7 million years ago.  Convergent evolution explains why haringtonhippus horses anatomically resembled Old World asses.  Both evolved long slender limbs as an adaptation to arid environments.

Fossil remains of Haringtonhippus francisi  have been found in east Texas, eastern Mexico, Kansas, Nevada, California, the Yukon, and Alaska.  Stilt-legged horse fossils are known from sites thought to be 3 million years old, and they occurred until as recently as 12,000 years ago about the time man became prevalent on the continent.

If scientists are able to extract DNA from even more ancient extinct genera of horses, they may be able to straighten out horse evolution.  Many biology textbooks use the fossil record of horses and their ancestors as an example of evolution, but these family trees are based on anatomical analyses that can be misleading.  DNA evidence would produce more reliable family trees.

Reference:

Heinztman, P; et. al.

“A New Genus of Horse from Pleistocene North America”

Genomics and Evolutionary Biology Nov. 2017

Raccoon (Procyon lotor) and Swamp Rabbit (Sylvilagus aquaticus) Latrines

January 23, 2018

Many animals defecate to mark their territory, but raccoons share communal latrines where all the individuals in an area deposit their feces. Communal raccoon latrines impact the ecosystem. The raccoon roundworm (Baylisascaris procyonis) is a parasite that spends part of its lifecycle in a raccoon’s intestine. Raccoons can live with this parasite, but it can kill mice, birds, and humans. Therefore, mice and birds avoid raccoon latrines, despite the nutritional value found in undigested seeds embedded in raccoon feces. Somehow, they evolved the ability to sense the danger of a parasite playground. However, raccoon roundworm is not dangerous to rats, so raccoon latrines actually attract rats seeking edible seeds. Seeds that survive transport through a raccoon’s digestive system and are overlooked by rats may then germinate. Raccoon’s play a role in the dispersal of some plant species.

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Raccoon latrine.  This batch is full of blackberry seeds.

Unlike raccoons, swamp rabbits don’t defecate in communal latrines, but oddly enough they often crap on moss-covered stumps or fallen logs. Perhaps the moss disguises the odor, preventing predators from triangulating their scent. It is also elevated, so a predator following its nose might miss it.  Researchers surveying swamp rabbit populations use these latrines to record their presence because this nocturnal species is difficult to find in the thick swamps and wetlands where they range.

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Swamp rabbit latrine. Note the moss.

Swamp rabbits are a species of cottontail that inhabits aquatic habitats from the Mississippi River Valley east to western Georgia and northwestern South Carolina. Another species of semi-aquatic cottontail–the marsh rabbit (S. palustris)–inhabits wetlands from western Georgia to the Atlantic Ocean and throughout all of Florida. There is little overlap between the 2 species, though they occupy the same ecological niche. How curious?

Swamp rabbit genetics has rarely been studied. A 20 year old genetic study determined swamp rabbits and marsh rabbits are closely related sister species, but this doesn’t explain why their ranges don’t overlap. So far, no geneticist has employed a molecular clock to estimate when swamp rabbits and marsh rabbits diverged or when they diverged from eastern cottontails (S. floridanus). The latter is an habitat generalist with an extensive Pleistocene fossil record. Specimens of Pleistocene eastern cottontails have been found all over North America. By contrast marsh rabbit remains dating to the Pleistocene are restricted to 8 sites in Florida and 1 site near the Georgia coast. Pleistocene swamp rabbit remains are even less common, having been discovered at 1 site in Missouri, and 1 site in Tennessee where Pleistocene remains were mixed with Holocene material, so this specimen might not even be from the Pleistocene. Some marsh rabbit remains date to the Sangamonian Interglacial (132,000 years BP-118,000 years BP). Swamp rabbits, as a species, are probably at least that old too. Both species thrived during wetter stages of climate when wetland habitat expanded. I hypothesize the common ancestor of both was a semi-aquatic species that was isolated into 2 separate founder populations during arid Ice Ages when unsuitable desert grassland habitat expanded between refuges along the Mississippi River Valley and Florida. But I still can’t figure out why they haven’t invaded each other’s ranges since then.

Genetic studies may be the best way to resolve this mystery because the fossil evidence is scant. I hope a geneticist takes an interest in this unresolved secret of nature.

References:

Fantz, Debbie; et. al.

“Swamp Rabbit Distribution on the Northern Edge of their Range in Missouri”

Southeastern Naturalist  16 (4) 2017

Halanych, K.; T. Robingon

“Phylogenetic Relationships of Cottontail (Sylvilagus, Lagamorpha) Congruence of 125r DNA and Cytogenetic Data”

Molecular Phylogenetics and Evolution 7 (3) June 1997

Weinstein, Sara; et. al.

“Fear of Feces? Trade-offs between Disease Risk and Foraging Drive Animal Activity around Raccoon Latrines”

Oikos  Jan 2018

The Presence of Caribou in Southeastern North America during the Pleistocene and it Paleoecological Implications

December 19, 2017

 

The reindeer, legendary conveyor of Santa’s sleigh, is an Holarctic animal, meaning it lives south of the Arctic Circle in both North America and Eurasia.  In North America the reindeer is more commonly known as caribou.  When Europeans colonized the New World caribou lived as far south as upstate New York, but today their range in North America is restricted to Canada and Alaska.  During Ice Ages, however, almost all of their present day range was under glaciers–unsuitable habitat even for such a cold hardy animal.  Caribou range shifted south then, and caribou fossil material has been found at numerous southeastern sites including Bell Cave in Alabama, Yarbrough Cave in Georgia, 3 caves in Tennessee, off the North Carolina coast, off Myrtle Beach, and in Charleston, South Carolina (the most southeastern known occurrence).  Apparently, caribou occurred at least as far south as the piedmont region.

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Reindeer and Caribou are the same species.
Caribou fossils have been found associated with an interesting mix of species at the above-mentioned fossil sites, though it’s unclear if they all lived at those localities during the same climatic phases.  Cave and offshore sites can collect the bones of animals from many different time periods.  Nevertheless, caribou bones have been found with the remains of giant beavers, flat-headed peccary, long-nosed peccary, woodland muskox, white tail deer, stag-moose, horse, tapir, mastodon, ground sloth, jaguar, and dire wolf.  Pleistocene caribou in eastern North America likely preferred open spruce woodlands interspersed with prairies.  This habitat would have also been favorable for horse, flat-headed peccary, bison, and mammoth.  By chance caribou remains haven’t been found with the latter 2, but they probably co-occurred at some locations.  Dire wolves, habitat generalists, likely co-occurred with caribou as well and probably preyed on them.
Baker Bluff Cave in northeastern Tennessee has well stratified deposits that contain many vertebrate bones from 2 different climate phases.  Information from this site can help determine the faunal composition that co-occurred with caribou.  The oldest deposits at Baker Bluff Cave are interpreted as representing a temperate forest consisting of oak, northern pine, birch, beech, etc.  Gradually, this environment gave way to the open spruce woodland/prairie as the climate became colder and drier during the Last Glacial Maximum.  White-tailed deer remains are abundant throughout all layers of the deposit, and they co-occur with caribou in Canada today, so undoubtedly they were a contemporary of Pleistocene caribou.  Long-nosed peccary, a forest edge species, like white-tail deer, likely co-occurred with caribou as well.  Mastodon, giant beaver, and stag-moose inhabited wetland environments adjacent to caribou habitat, and I’m certain they were contemporaries with caribou.  Woodland musk-ox, another likely contemporary, foraged in shrub habitat near caribou range.
A jaguar tooth found at Baker’s Bluff Cave was excavated from the lowest oldest level.  This is evidence Pleistocene jaguars inhabited cool temperate forests, but it seems unlikely they survived in the region when the forest gave way to boreal environments.  However, caribou may have also occurred in the southeast during interstadials.  (Good carbon-dating of regional caribou fossils has yet to be conducted.)  It’s impossible to determine from available data whether jaguars inhabited the same range as caribou.  The same can be said for the tapir, a species that preferred thick forest.
Cave deposits contain an even greater abundance of small vertebrate fossils.  Most smaller animals are more restricted to certain environments than larger species, and their composition better reveals what natural communities of this locality were like.  The Baker Bluff Cave deposits are particularly interesting.  Fossil material of species still found in the region today (gray squirrels, eastern chipmunks, southern flying squirrels) were present throughout the deposit but were less common during the open spruce woodland/prairie phase.  By contrast some species that today live to the north and west of the region (13-lined ground squirrels, least chipmunks, northern flying squirrels, badgers, pine martens, fishers, magpies) were also found throughout the deposit but were less common during the cool temperate forest stage.  Red squirrels were also less common during this phase but more common after the landscape changed.  Fossil remains of 13-lined ground squirrels have been excavated from sites throughout the southeast but no longer occur east of the Mississippi.  Fossil material of birds that prefer open spaces such as upland sandpiper and prairie chicken were excavated from Bell Cave and Yarbrough Cave.  The presence of these species is evidence prairie habitat was common in the region during Ice Ages.  Pine marten specimens, dating to the Pleistocene, were discovered as far south as northern Alabama, and Pleistocene fisher specimens turned up in northern Alabama and north Georgia.  This is evidence of boreal environments in the upper south.
I hypothesize Ice Age ecosystems in southeastern North America were more diverse than they are today due to rapid climate fluctuations.  Climate phases of warm wet interstadials (but cooler on average than today) and cold arid stadials alternated but the response of the floral and faunal composition to these rapid climate changes lagged behind.  Some climate phases lasted for a few thousand years or perhaps just centuries or even decades.  They weren’t long enough to completely eliminate habitat for species with warm temperate affinities, nor did they last long enough to extirpate habitat favorable for species with boreal affinities.  This explains why eastern chipmunks co-occurred with least chipmunks, and why caribou may have shared the range with jaguars and tapirs.  During cold phases though prairie and boreal forest expanded, oak woodlands persisted on some tracts of land, especially south-facing slopes.  During warm phases oak woodlands expanded, but spruce forests persisted on north facing slopes.
Herds of caribou formerly wandered through Georgia followed by packs of dire wolves and prides of lions.  The herds traveled through fingers of prairie between open woods consisting of pine and spruce and oak where turkeys foraged on the ground and fishers chased gray squirrels through the tree tops.  Landscapes of present day Georgia are unrecognizable by comparison.
Reference:
Guilday, John; H. Hamilton, E. Anderson, and P. Parmalee
“The Baker Bluff Cave Deposit, and the Late Pleistocene Faunal Gradient”
Bulletin of the Carnegie Museum 1978

The Large Otter (Enhydritherium terraenovae) of Miocene North America

December 13, 2017

A large otter lived across North America during the Miocene and early Pliocene from at least 6.5 million years BP to about 4.5 million years ago.  Fossils of this extinct species weren’t discovered until 1985 at a site known as Palmetto Mine located in Florida.  Scientists examined the material (a jaw and teeth) and gave it the scientific name Enhydritherium terranovae.  They assumed this species of otter subsisted mostly on marine shellfish because its teeth resembled that of the extant sea otter (Enhydra lutra).  Though sea otters eat some fish and cephalopods, a great part of their diet consists of shellfish. However, a nearly complete skeleton was later discovered at the Moss Acres Race Track site located about 75 miles from where the coastline was when the specimen died.  A concentration of fish bones, otherwise rare at the site, was found in the matrix alongside the otter specimen.  Scientists interpreted the concentration of fish bones as the stomach contents of this particular otter.  This species ate fish and shellfish.  Scientists now believed Enhydritherium occupied both fresh and salt water habitats, but still thought of it as a coastal species.  Fossil remains of Enhydritherium have been discovered at 8 sites in Florida and 3 in California, so scientists wondered how a coastal species dispersed from Florida to California.  A recent discovery of Enhydritherium bones in Mexico about 125 miles from the Gulf of Mexico (and even farther from the Pacific) solves this mystery. Enhydritherium was not a coastal species, but instead occurred in freshwater habitats well inland.  Enhydritherium likely followed river systems and could travel overland for considerable distances between water sheds much like modern day river otters (Lontra canadensis) do.  I’ve seen road-killed river otters and beavers many miles from the nearest creek.

Enhydritherium exceeded the size of all extant species of otter.  They averaged 50-100 lbs.  By contrast sea otters and the giant otter of South America (Pteronura brasiliensis) normally reach maximum weights of 75 lbs. Enhydritherium also differed from modern otters in the way they swam.  Modern otters use all 4 limbs but rely primarily on their legs when they swim.  Enhydritherium had robust forelimbs, and most of their propulsion came from their arms instead of their legs.

At the Moss Acres Race Track site the Enhydritherium skeleton was found in association with the bones of rhino, horse, gompothere, and borophagine dog.  Rhinos became extinct in North America about the same time Enhydritherium did.  This faunal turnover occurred when Ice Ages began cycling.  Nevertheless, Florida, southern California, and Mexico remained subtropical during Ice Ages. Pollen evidence from the Moss Acres Race Track included oak, pine, and grass; but no tropical species.  The reason for the end of Miocene faunal turnover is unknown and probably complex.  Perhaps ecological changes caused by climate change and competition with new species were factors.

Today, there are 13 species of otters in the world.  The North American river otter and the Eurasian otter (Lontra lutra) probably descend from an extinct genus known as Satherium which was widespread during the Pliocene.  Several South American species may also descend from this genus, but genetic analysis suggests the giant otter of Brazil is most closely related to the smooth-coated otter of the Far East.  Evidentally, there was more than 1 otter dispersal from Eurasia to the Americas.

River otter fossil material is fairly common at Pleistocene-aged fossil sites in southeastern North America including Ladds, Bartow County, Georgia.  They thrive wherever they can find enough fish to eat.  Presently in Georgia, river otters are most abundant in coastal plain rivers and salt marshes, but their population gradually decreases upriver until they are rare but present in the mountain region.  I’ve been seeing more road-killed otters in recent years.  Maybe it is coincidence, but I believe fur-trapping in going out of style, and river otters are on the increase as a result.

References:

Lambert, W.D.

“The Osteology and Paleoecology of the Giant Otter Enhydritherium terraenovae”

Journal of Vertebrate Paleontology 17 1997

Tseng, Jack Z.; et. al.

“Discovery of the Fossil Otter (Enhydritherium terranovae) Carnivora; Mammalia in Mexico Resolves a Paleoecological Mystery

Biology Letters 13 (6) June 2017

https://www.floridamuseum.ufl.edu/florida-vertebrate-fossils/species/enhydritherium-terraenovae/

 

Capybaras and Hippos Take II

December 6, 2017

(Note: I tried publishing this post yesterday but due to undetermined technical difficulties the text disappeared.  Hopefully, this entry will have text.)

I planned on writing a blog article about Pleistocene capybaras of southeastern North America, but when I began researching the topic on google I discovered I’d already written a pretty good essay 2 years ago.  (See: https://markgelbart.wordpress.com/2015/12/07/megafauna-habitat-modification-and-pleistocene-capybaras-in-southeastern-north-america/https://markgelbart.wordpress.com/2015/12/07/megafauna-habitat-modification-and-pleistocene-capybaras-in-southeastern-north-america/ ) I’ve written 601 articles for my blog, and it’s hard for me to remember everything I’ve already covered.  Much to my disappointment, there has been little recent academic research about the extinct species of capybaras.  There were 2 species that lived in Florida, Georgia, South Carolina, and probably the Gulf States during the Pleistocene–Neochoerus pinkneyi  and Hydrochoerus holmesi.  Both were more than twice as large as the 2 extant species of capybaras that are presently confined to Central and South America near the equator.  I hypothesize the extinct species could endure somewhat colder air temperatures than their modern day kin due to their larger size.  Nevertheless, they probably extended their range during warmer wetter climate cycles. In my previous blog entry linked above  I think I mentioned how capybaras occupy an ecological niche similar to that occupied by African hippos.  Both are aquatic species that graze adjacent water’s edge marshes into lawn-like environments.  But I didn’t note the remarkable evolutionary convergence in the physical appearance between the 2 unrelated animals.

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Capybara and young.

Convergent evolution is when 2 unrelated organisms evolve similar characteristics to adapt to similar environments.  Capybaras and hippos have similar height to weight ratios.  They also share other characteristics such as small round ears, short necks, square faces, and thick hides.

Hippos remind me of ancient extinct animals from earlier ages…like the kind of monstrous beasts of the Miocene or Eocene.  They should be appreciated for their resemblance to primitive extinct evolutionary dead-ends and ancestral species.  Hippos are most closely related to whales, having shared a common ancestor 28 million years ago known as Epirigenys lokonensis. Hippos resemble the primitive ancestors of whales.

Several extinct species of hippos were widespread in Europe during the Pleistocene but disappeared during the Last Glacial Maximum when available habitat shrank into small refugia where they were more easily hunted into extinction by man. Several species of hippos were also driven into extinction when man colonized Madagascar.  Dwarf species of hippos lived on the Mediterranean Islands of Crete, Cyprus, Sicily, and Malta until man discovered those places.  Just 2 extant species of hippo remain —Hippopotamus amphibious and Hexaprotodon lieberiensis. 

Hippos are the most dangerous non-human vertebrate in Africa.  They are responsible for an average of 2900 deaths every year.  However, mosquitoes and flies spread tropical diseases that kill about 655,000 people annually.  Paradoxically, these tiny pests are a greater hazard than a 2 ton hippo.

 

 

The Sitzkrieg Hypothesis

November 21, 2017

The authors of a new statistical analysis of megafauna extinctions boast their method is superior to previous efforts, and they can’t reject human interactions as a cause of the extinctions.  However, they also can’t rule out climate change as a factor, so despite their supposed superior method, their new study (referenced below) resolves nothing.  The statistical method they used is known as kriging, a kind of interpolated algorithm.  The data included 95 of the last radiocarbon dates of megafauna species and 75 of the earliest dated archaeological sites in North America.  They then mapped the last appearance dates of the megafauna with the earliest archaeological evidence of humans.  They concluded climate change caused the extinction of mastodons in Alaska because this species disappeared there long before humans colonized the region, but humans may have been a factor causing extinctions at lower latitudes.  Megafauna persisted until the very end of the Pleistocene in some regions including Mexico, Texas, Tennessee, and the Great Lakes region.  Humans may have overlapped in these regions for as long as 3000 years.  The study doesn’t find much evidence for the blitzkrieg (rapid overhunting) model of extinction, though there may have been “localized” examples of this in western North America.  But it is possible humans gradually disrupted ecosystems in a way that was detrimental to megafauna populations.  This is known as the sitzkrieg model of extinction, and it is the scenario that makes the most sense to me.

There is a major flaw in the reasoning behind the conclusions of this study.  The authors of this study equate the regional disappearance of a species with its extinction.  For example mastodons became extirpated in Alaska about 30,000 years ago, but they did not become extinct.  Populations remained robust south of the ice sheet until about 13,000 years ago.  If man never colonized North America, it seems likely mastodons would have re-colonized Alaska and Canada during the present day interglacial.  Habitat in present day Canada and Alaska is very much like that of some Ice Age regions mastodons formerly inhabited before their extinction.  Mastodons were a wetland species, and aquatic habitats have greatly expanded in Canada and Alaska since the end of the Ice Age.  (During the Last Glacial Maximum Canada was covered by ice sheets and Alaska was an arid grassland–both unsuitable environments for mastodons.)  Climate change may have driven the redistribution of megafauna geographic ranges, but that is not the same as extinction.  During climate phases that favored the expansion of grassland, woodland species were forced to migrate farther to find suitable habitat, and vice versa.  Again, this is not extinction…it is a species adjusting to a new range map.

I’m convinced man, and man alone, is responsible for the extinction of the Pleistocene megafauna.  These wide-ranging species (some occurred all across the continent) were adaptable species that survived dozens, if not hundreds, of dramatic climatic swings over hundreds of thousands of years.  But when man begins to appear in the archeological record, they disappear permanently.  There is no way that can be coincidental. I think man disrupted the ecological balance through a combination of overhunting, increased fire frequency, and interdiction of migratory corridors.  It took a few thousand years, but when human populations reached a certain level, most species of megafauna could not adapt.  They required an ecosystem with low levels of people and did even better with no humans on the landscape at all.

Image result for Greenland temperature graphs for last 120,000 years

Graph of average annual temperatures over the past 150,000 years based on data from Greenland ice cores.  Note all of the dramatic climate fluctuations.  Megafauna species survived these climate fluctuations but became extinct in North and South America within a few thousand years of when man entered the continents.

Reference:

Weatherall, M.; Brianna McHorse, and E. Davis

“Spatially Explicit Analysis Sheds New Light on the Pleistocene Megafaunal Extinctions in North America”

Paleobiology November 2017