A Relic Population of Pleistocene Man (Homo sapiens) on North Sentinel Island

March 22, 2018

Homo sapiens first left Africa about 60,000 years ago.  Most of the original tribes that left Africa either perished in the harsh environments of Asia or were replaced by later arriving tribes that had developed superior technology or subsistence strategies.  The people who eventually conquered Asia look and behave quite differently from the initial African colonizers.  However, there is a relic population of early Homo sapiens on the Andaman Islands located in the Bay of Bengal near Malaysia.  Scientists believe a land bridge connected the Andaman Islands with Malaysia during Ice Ages and early Homo sapiens walked there.  Rising sea levels isolated the Andamanese and protected them from being killed or assimilated by groups that later conquered Asia.  Genetic evidence suggests the Andaman Islanders diverged from the rest of humanity 60,000 years ago.

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Location of the Andaman Islands.  They were connected to Malaysia during Ice Ages due to lower sea levels.

The Andaman Islanders are related to African pygmies but are considered negrittos–people smaller than average in size but larger than pygmies.  This smaller stature probably helps them survive on islands where they have less food.  It’s an evolutionary advantage to have lower caloric intake needs on islands, and dwarfism is common among large species of mammals that became trapped on islands.  People on 1 particular Andaman Island known as North Sentinel have been isolated longer than any other Andaman Islanders.  Their language is far different from the 2 languages spoken on the other Andaman Islands, and they have incredibly primitive technology.  All attempts to communicate with them have failed because no one in the outside world understands their language. The North Sentinelese kill outsiders on sight, explaining why they have been isolated for so long.  They have no agriculture, and some believe they depend on lightning strikes for fire, though I doubt this.  I think our evolutionary ancestors (H. heidelbergensis and H. erectus) had fire, but who knows–maybe the North Sentinelese forgot fire-making knowledge.

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The unfriendly North Sentinelese attack outsiders on sight.  Here, they are about to shoot arrows at a passing helicopter. Note the red-ochre painted faces.

There are only 40-400 North Sentinelese living on the 24 square mile island.  The island vegetation prevents an aerial survey of the population.  They eat wild pigs, fish and shellfish, and wild plant foods.  The Indian government (owners of the Andaman Islands) abandoned attempts to contact the tribe and outlawed other outsiders from visiting the island.  It’s unsafe for outsiders because they will be attacked, and introduction of infectious diseases would probably wipe out North Sentinelese because their immune systems have been isolated from other humans for so long.  The North Sentinelese recently murdered 2 drunken fishermen who drifted too close to shore.  Also not long ago, a typhoon wrecked an oil tanker on a coral reef off the island, and the crew had to fight for their lives before being rescued.  The North Sentinelese stripped the ship bare.  They shoot arrows at all passing helicopters.

The North Sentinelese represent what Pleistocene man was like 60,000 years ago.  Pleistocene people were small of stature and dark-skinned.  Genetic evidence of a 10,000 year old skeleton in Britain suggests even some Europeans were dark-skinned during the Pleistocene.  They had primitive technology and were hostile to strangers.  The descendants of these small violent humans conquered the world.


Endicott, P. et. al.

“The Genetic Origins of the Andaman Islanders”

American Journal of Human Genetics  72 (1) 2003


An Extinct Map Turtle (Graptemys kerneri) and Pleistocene Sea Level Fluctuations

March 15, 2018

Most species of freshwater turtles can travel overland and occupy new favorable habitat, promoting genetic vigor within the meta population.  They often move between watersheds, and this explains why so many species have such a continuous geographic range.  I’ve seen snapping turtles (Chelydra serpentina) and yellow-bellied sliders (Chrysemys scripta) a considerable distance from any water source.  However, map turtles in the Graptemys genus (10 species) do not travel overland, and their ranges are usually restricted to single river drainages.  So how did closely related Graptemys species colonize different river drainages even though they don’t travel overland?  The dispersal of the Graptemys genus is closely related to Pleistocene sea level fluctuations.

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Barbour’s map turtle is the closest living relative of the extinct Kerner’s map turtle.

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Barbour’s map turtle range.  Note how it is restricted to 1 river system.

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Map of Florida during the Last Glacial Maximum.  Different rivers in Florida isolated by sea level rise today were interconnected on land exposed on the continental shelf due to sea level fall.  This allowed map turtles to colonize adjacent rivers systems where they evolved into distinct species following sea level rise and isolation of populations.

During Ice Ages sea level fell because so much of earth’s atmospheric water became locked in glacial ice.  In Florida dry land habitat extended 120 miles west into the Gulf of Mexico.  Several of Florida’s river systems that are isolated from each other today by sea level rise were interconnected during the Last Glacial Maximum on the land that was exposed by ocean recession.  This allowed an ancestral population of Barbour’s map turtle (Graptemys barbouri), a species today restricted to the Apalachicola-Flint-Chattahoochee River System, to colonize several other rivers in Florida.  Subsequent sea level rise isolated this founder population in the Suwanee, Santa Fe, and Waccasassa Rivers where they evolved into a now extinct species known as Kerner’s map turtle.  Specimens of this species have been found in all 3 of the above mentioned rivers in Florida, and the type specimen (a complete skull) came from the Suwannee.

Kerner’s map turtle had a wider shorter skull than any extant species of map turtle.  Morphologically, it most closely resembles Barbour’s map turtle, the extant species that has the widest shortest skull among living Graptemys turtles.  There is an east-west gradient in the shape of map turtle skulls.  Western species have narrower longer skulls, but map turtle species’ skulls get shorter and wider the farther east they occur.  Kerner’s map turtle was the easternmost species, and it ranged into north central Florida and possibly southeastern Georgia where the Suwannee River headwaters originate.  Rare earth element analysis indicates Kerner’s map turtle lived during the Rancholabrean Age (300,000 years BP-11,000 years BP).  There are no known Graptemys specimens older than the mid-Pleistocene.  The extinction of Kerner’s map turtle likely occurred during a dry climate stage of the mid-Holocene (~6,000 years BP).  Map turtles require fast moving high water where they can disburse up and down rivers.  But drought turns their habitat into stagnant isolated pools that can also be detrimental to their favorite food source–freshwater mussels.  Other species of freshwater turtles and alligators can survive these conditions by moving overland until they find good habitat, but map turtles don’t travel overland.  That’s why most species are restricted to major rivers that rarely, if ever, suffer sporadic flows.

The founding species in the Graptemys genus undoubtedly evolved in the Mississippi River.  Almost all other species exist in other river systems that empty into the Gulf of Mexico.  Pleistocene sea level fluctuations facilitated the colonization and speciation of map turtles in the Apalachicola River drainage, the Guadulupe River System, the Pascagoula River, Mobile Bay drainage, Yellow River System, and Pearl River.  Different map turtle species live in each.  Ocean recession allowed the rivers to become interconnected on the continental shelf, and map turtles were able to colonize adjacent river systems; then sea level rise isolated populations, causing speciation.


Ehret, Dana; and J. Bourque

“An Extinct Map Turtle Graptemys kerneri (Testudinae, Emydidae) from the Late Pleistocene of Florida”

Journal of Vertebrate Paleontology 31 (3) May 2011

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.


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.


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.


Muttoni G.; Giancarlo Scardio, and Dennis Kane

“Early Hominins in Europe: The Galerian Migration Hypothesis”

Quaternary Science Review 180 Jan 2018

Late Miocene/Early Pliocene Climate Change Caused Sudden Burst of Warbler Speciation

February 18, 2018

I had a good birding day a few weeks ago.  I was walking alongside Woodbridge Lake in Evans, Georgia, and I saw many of the aquatic species I almost always see there–Canadian geese, mallard ducks, pied-billed grebes, cormorants, great blue heron, and great egret.  But much to my surprise, I also saw an immature bald eagle.  When I first spotted it, I assumed it was a black vulture because there was a flock of those scavengers soaring over the lake.  The eagle briefly flew low enough for me to identify it.  A couple osprey were soaring above the eagle, and I wonder if the young eagle was following them to supplement its diet.  Eagles are notorious for stealing fish from ospreys.  A lone Cooper’s hawk was another unexpected species to make my birding list that day.  Away from the water I saw a small flock of pine warblers (Setophaga pinus) roosting near the top of a pine tree.  Pine warblers are the only year round resident warbler species in southeastern North America.  Myrtle warblers (Dendroica coronata) spend winters in the south, and many warbler species either spend summers in the region or pass through during spring and fall on their migrations north and south.  This sighting made me curious about the fossil record of warblers, so I did an internet search.  As far as I could determine, fossil evidence of warblers is non-existent.  This is not surprising.  Warblers inhabit forest environments where their remains are not likely to be preserved.  However, I did come across an interesting genetic study that determined a sudden burst of warbler speciation occurred during the late Miocene/early Pliocene.

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I thought these were pine warblers, but a reader identified them as cedar waxwings, and I agree.  Nevertheless, my mistaken id inspired this blog entry.  I took this photo a few weeks ago.

This speciation event occurred between 4.5 million years BP-7 million years BP when climate became warmer and drier.  The authors of this study note this coincides with a time of faunal turnover.  Rhinos and species of 3-toed horses became extinct when warblers speciated into many different species.  They conclude the aridity fragmented forests, isolating many different populations of warblers that then evolved into unique species.  It’s a remarkable example of adaptive radiation, defined as the evolutionary lineage differentiation into a suite of closely related species differing in their use of ecological resources.  It resulted in the evolution of over 2 dozen species.  Warbler adaptive radiation differs from that of other species groups because there is little morphological difference between the species.  Darwin’s famous Galapagos Island finches evolved different bills depending upon which ecological niche they inhabited, but warblers remained very similar.

By the middle of the Pliocene, habitats began to resemble those that exist today (if left alone by man), and warbler speciation slowed down because existing species came into contact with each other and competed for all of the existing niches.  Still, the evolution of a few species may be linked to glacial/interglacial cycles.  Townsend’s warbler (D. townsendi), hermit warblers (D. occidentalis), and black-throated green warblers (D. virens) may have speciated during the Pleistocene.  Black-throated gray warblers (D. nigrescens ) and Grace’s warbler (D. gracae) may be the result of hybridization events.

The pine warblers of the south are closely related to the founder population of warblers.  The ancestors of all warblers likely were a more adaptable species, like the pine warbler, and less dependent upon migration for survival.  Pine warblers are 1 of the few warbler species that can feed upon seeds.  Most warbler species eat insects and fruit and thus require warmer temperatures.

Rapid adaptive radiation among mammals, like warbler speciation, followed a similar pattern after dinosaurs became extinct.  There was a sudden burst of speciation of mammals occupying newly available niches vacated by dinosaurs.  But the rate of speciation slowed down when enough species evolved that competition increased for those niches.


Lovette, I.; and E. Bermingham

“Explosive Speciation in the New World Dendroica Warblers”

Royal Society of Biological Sciences 1999

Pleistocene Squid

February 11, 2018

The cephalopods were the most intelligent creatures on earth for hundreds of millions of years.  Nectocurus pteryx, a squid-like ancestor of all cephalopods, lived 500 million years ago during the Cambrian Age.  Fossil specimens of this species are found in the famous Burgess Shales.  Cephalopods–a group that includes squid, octopus, cuttlefish, nautiloids, and the extinct ammonites–evolved arms they can use to manipulate objects, and squid, through convergent evolution, evolved eyes quite similar to the human eye, so they can see the world like we do.  This explains how they evolved intelligence much greater than that of other invertebrates.

This blog article, like my entry about Pleistocene spiders, is entirely speculative because cephalopods have soft bodies that are also rarely preserved.  During Ice Ages sea levels receded and dry land extended across the continental shelf, today inundated by ocean water.  It seems likely deep water species of squid inhabited waters adjacent to the shore because steep drop-offs existed much closer to land during these climatic stages.  Giant squid (Architeuthis dux), reaching lengths of 43 feet, and colossal squid (Mesonychoteuthis hamiltoni), almost as long, probably lurked near the coast, whereas today they are normally restricted to deeper waters far out to sea.

The Gulf Stream current that keeps land temperatures moderate in the northern hemisphere often shut down or was greatly reduced during episodes of glacial meltwater influxes known as Heinrich Events.  These must have had an impact on squid migration.  Many species of squid migrate long distances to spawning grounds, and Heinrich Events must have altered their paths of movement, species abundance, and species composition.  Large die-offs probably occurred in some species, while others may have benefitted from the chaos.

Squid are an important food source for marine mammals, and deep sea species of whales likely ventured closer to shore in search of squid during Ice Ages.  Seals then living on the shores of the Atlantic Coastal Plain fed on squid.

The composition and species abundance of squid during various stages of the Pleistocene will forever remain a mystery.  There are over 300 known species of squid in the world today, but scientists know little about squid species abundance of the present day, let alone of the distant past.  One study of squid off the eastern coast of Florida determined eye flash squid (Abralia cf veranyi), flying squid (Ommastrephidae sp.), and shortfin squid (Illex sp.) were the 3 most abundant genera or families.

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Eye flash squid are 1 of the most common species found off the coast of eastern Florida.

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Shortfin squid–another common species.

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Flying squid shoot out of the water to escape predators.  


Sperm whales feed mostly on squid.  Individuals can be distinguished by scars from battles with giant squid.

I’m not impressed with the flavor of calamari.  I’ve had it in a Vietnamese pho soup.  The soup itself was delicious, but the calamari was rubbery and tasteless.  I’ve tried fried calamari but this too had no flavor.  The best squid I’ve ever eaten was a canned Korean product.  The squid, packed like sardines, were seasoned with soy sauce and sugar.  The seasoning would’ve made anything taste good.  However, the squid were not cleaned, and I had to be careful chewing so I wouldn’t break a tooth on the hard beaks.


Erickson, Carrie; Clyde Roper and Michael Vecchione

“Variability of Paralarval-Squid Occurrence in Meter-net Tows from East of Florida, USA”

Southeastern Naturalist 16 (4) 2017


The Pleistocene Range Extension of the American Alligator (Alligator mississippiensis)

February 4, 2018

Paleontologists excavated 6 artesian springs along the Pomme de Terre River in Missouri before they were inundated by a reservoir about 40 years ago.  They recovered many bones of Pleistocene vertebrates, including the remains of 71 mastodons, along with invertebrate material, plant macrofossils, and pollen.  The scientists published their data in 1 of the papers referenced below.  This is 1 of my favorite studies because the subfossil evidence shows how the local environment changed over time.  During a warm interstadial over 40,000 years ago the region was dominated by hardwood forests of oak, hickory, maple, juniper, dogwood, hornbeam, honey locust, ash, cherry, plum, and Osage orange.  As the climate became cooler and more arid, jack pine and prairie expanded on poor soils, while oak was restricted to richer sites.  When the full glacial maximum struck, the environment transformed into an open spruce parkland landscape where spruce had previously been absent.  The remains of at least 2 alligators were recovered from the deposit dating to the warm interstadial.  This is the northernmost known occurrence in the fossil record of Alligator mississippiensis, and it is approximately 300 miles north of its present day range.  The alligator specimens were found associated with the bones of box turtles, soft shelled turtles, ducks, Harlan’s ground sloth, gopher, giant beaver, raccoon, saber-tooth cat, mastodon, mammoth, horse, tapir, camel, white-tail deer, long-horned bison, and woodland muskox.

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Current range map of the American alligator.  There is a disjunct population in northern Alabama introduced by man but not noted on this map.  Note the northcentral bulge in this species’ range toward its northernmost Pleistocene occurrence in northwestern Missouri.  Pet alligators released in southern Ohio today at approximately the same latitude can survive but can’t reproduce.

The only other possible known occurrence of A. mississippiensis north of its present day range is from Ladds in Bartow County, Georgia; but I think the paper that referenced this did so in error.  The paper (also referenced below) contains a checklist of all vertebrate species known to have occurred in southeastern North America during the Pleistocene, and alligator is noted as being reported from Ladds.  However, I’ve read all the published data about Ladds, and there is no mention of alligator specimens from this site.  The supposed specimen is also not listed in the paleobiology database.  It’s possible (perhaps even probable) alligators occurred in Bartow County, Georgia during warmer climate phases because north Georgia is much lower in latitude than northwestern Missouri where their remains have been found.  If anyone knows of a Bartow County alligator specimen, please contact me.

Some scientists may think the presence of alligators north of their present day range is evidence of temperatures warmer than those of today, but this isn’t necessarily the case. Instead, Ice Ages caused a retraction in the pre-historic range of the alligator, and they perchance have failed to recolonize all of their former stomping grounds.  If average temperatures continue to increase as predicted, alligators may yet expand their range farther north. It’s also possible alligators are able to extend their range during cycles of reduced seasonality.  The earth goes through cycles when it tilts to a lesser degree than it does now causing milder winters but cooler summers.  Annual average temperatures were the same as they are today but more evenly distributed throughout the year.

Alligators are better adapted to colder climate than any other species of crocodilian.  For example during unusual cold spells American crocodiles (Crocodylus acutus) bask in the sun in an attempt to warm themselves and they often perish, but alligators seek shelter in water, and if temperatures drop too much, they live but go dormant.  Adult alligators can survive quite cold temperatures.  In the northern parts of their range alligator reproduction becomes sporadic.  Though adult alligators can survive severe cold spells, juveniles die.  Alligators require several mild winters in a row before their young get large enough to survive an harsh winter.  Cooler summers and springs will result in an all female population–another potential limiting factor in the northern parts of their range.  Alligator eggs in nests with temperatures that fall below 86 degrees F become female.  Nests are warmer than air temperatures due to composting vegetation, but they can still cool, if the surrounding temperatures are low.  Eggs won’t hatch at all when nest temperatures fall below 80 degrees F.  Either decades of severe winters or cool spring/summers or both probably caused the extirpation of the alligator in Missouri during the late Pleistocene.

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Alligator brumating (going dormant) in ice.

The American alligator is an extremely adaptable species having survived countless climatic changes.  It has existed relatively unchanged as a species for at least 5 million years.  Scientists aren’t even able to discern a definite difference between modern alligators and fossil specimens from 5-12 million years old, so the American alligator may be a 12 million year old species.  Alligators from the early Miocene are assigned to a different species (A. olseni), and this is the probable ancestor of the modern day alligator.  A. olseni specimens have been found in Tennessee, but climate was much warmer during the early Miocene than it is today.


King, James; and Jeff Saunders

“Environmental Insularity and the Extinction of the American Mastodont”

in Quaternary Extinctions: A Prehistoric Revolution  edited by Paul Martin and Richard Klein

University of Arizona Press 1984

Russell, D.A.; F. Rich, V. Schneider, J. Lynch-Stieglitz

“A Warm Thermal Enclave in the Late Pleistocene of the Southeastern U.S.

Biology Reviews 84 (2) May 2009

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.


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.


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