Archive for the ‘herpetology’ Category

Pleistocene Terrapins (Malaclemys terrapin)

March 20, 2017

Until recently, there was little fossil evidence of diamond-backed terrapins. This species inhabits salt marshes and mangrove swamps from the Gulf of Mexico to Cape Cod, Connecticut.  For most of the past 2 million years, sea level has been much lower than it is today due to the larger ice caps of long-lasting Ice Ages.  This means many potential fossil sites where the remains of terrapins might be found are submerged deep underwater and difficult to access.  Sea level has been the same or higher than it is today probably for less than 20% of the last million years, and this reduced the chances easily accessible fossil sites developed in salt marsh zones.  However, the remains of terrapins dating to the Pleistocene have been excavated from  3 sites in Florida, 1 in Georgia, and 1 in South Carolina.  These specimens weren’t described in the scientific literature until 2012.

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The diamond-backed terrapin is adapted to living in salt marshes.

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Diamond-backed terrapin habitat–a salt marsh.

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Diamond-backed terrapin range map.

The 3 sites in Florida where Pleistocene-age terrapin remains were discovered are Page-Ladson, Aucilla River, and Wekiva River.  Terrapin material turned up at Edisto Beach, South Carolina, and fossil hunters found terrapin bones in spoil piles dumped on Andrews Island, Georgia.  (All of Andrews Island is manmade, consisting of spoil piles dredged from the South Brunswick River, aka Fancy Bluff Creek. The Army Corps of Engineers periodically dredges the river to keep it deep enough for safe shipping. Plants have taken root there and it is an haven for wildlife.) The specimens are thought to be Pleistocene in age because they are associated with bones of other species that lived then.  The 3 sites in Florida and the 1 at Edisto Beach commonly yield bones of extinct Pleistocene mammals.  The spoil piles on Andrews Island contained the remains of snapping turtles (Chelydra serpentina), yellow-bellied cooters (Trachemys scripta), and the extinct giant tortoise (Hesperotestudo crassicutata).  These species all lived during the late Pleistocene.  The presence of these 3 species along with the terrapin indicates the local environment at the time of deposition was a brackish marsh bordering an open grassy savannah. Snapping turtles and yellow-bellied cooters are fresh water species that can tolerate brackish conditions, and giant tortoises preferred dry land environments.

Terrapins are not closely related to sea turtles.  Morphological and genetic evidence suggests they are most closely related to freshwater turtles in the Graptemys genus.  In North America this genus includes 10 species of map turtles and saw backs. Terrapins are the only turtle species uniquely adapted to live in salt marshes.  They have lachrymal salt glands that help them get rid of excess salt.  These are absent on all species of fresh water turtles.  Terrapins are also able to drink the layer of rain water that temporarily floats on top of salt water.  Terrapins feed upon shellfish–periwinkle snails are their favorite but they consume shrimp, crabs, and bivalves as well.

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The salt marsh periwinkle (Littorina irrorata) is the diamond-backed terrapin’s favorite food.

Terrapins were formerly so abundant they constituted the main source of protein for coastal slaves during the 18th and 19th century.  But a faddish craze for turtle soup circa 1900 greatly reduced their numbers.  All of the finest restaurants served turtle soup, and it was the most expensive item on the menu.  I’ve only had the opportunity to eat turtle meat once.  Turtle meat is very delicious, tasting like lobster.  Because terrapins feed on shellfish, their flesh likely reflects their diet.  Terrapins are presently a protected species but are still considered threatened.  Real estate development destroys their habitat, they drown in crab traps, cars run over them, and there are people who still eat them.  Egg-eating raccoons flourish as well, since most large predators that kept their population in check no longer exist on the east coast.  If I get the urge to eat turtle again, I’ll stick with the common snapping turtle which as their name suggests are still common.

Reference:

Ehret, Dana; and Benjamin Atkinson

“The Fossil Record of the Diamond-backed Terrapin, Malaclemys terrapin (Testudines: Emydidae)”

Journal of Herpetology 46 (3) September 2012

 

Pleistocene Rattlesnakes

September 29, 2016

Too many people have an irrational fear of snakes.  One of my neighbors was once frightened by an harmless garter snake a car had flattened like a tortilla in front of her house.  I have peeved more than 1 neighbor over the years by defending a rattlesnake’s right to life.  In my opinion rattlesnakes are an interesting member of the local fauna; less dangerous than big dogs, speeding cars, and lightning.  The odds of getting bitten by a rattlesnake are exceedingly small.  Rattlesnakes do not exist to bite people.  Instead, they want to eat small animals, mate, and stay warm.  They want larger animals, such as humans, to leave them alone.  The majority of snake bite victims stupidly handled the serpent and would have never been bitten, if they would have left it alone.  There is no reason to fear snakes, but they should be respected and not treated like a pet or a toy or as proof of faith in God.

Rattlesnakes are not considered endangered, but they were formerly more common prior to human settlement.  The first white men to explore Kentucky were constantly blundering into them. ( See: https://markgelbart.wordpress.com/2012/04/20/excerpts-from-the-journal-of-an-expedition-to-kentucky-in-1750/ ) Habitat loss and direct destruction during rattlesnake roundups greatly reduced their population.

Genetic evidence suggests the rattlesnakes first diverged from other pit vipers about 22 million years ago.  This divergence probably occurred in western North America because there are more species in that region than anywhere else.  There are 30 species of rattlesnakes, and all of them live in America.  Traditionally, herpetologists categorized 27 species in the crotalus genus and 3 in the sistrurus genus, but the most recent genetic analysis suggests 1 of the sistrurus species should be considered a crotalus.

There are 3 species of rattlesnakes that range throughout southeastern North America today–the eastern timber (Crotalus horridus), the eastern diamondback (C. adamanteus), and the pygmy (Sistrurus miliarus).  Evidence from the fossil record shows all 3 of these species have lived in the region since at least the late Pliocene over 2 million years ago.  However, the eastern timber rattlesnake is presently absent from peninsular Florida, but it did live there during the mid-Pleistocene.  This species probably became extirpated from the peninsula of Florida during a time of high sea levels when  most of the state was  inundated by ocean, and for some undetermined reason it has failed to recolonize its former territory.  I think its ecological niche is now occupied by the other 2 species of rattlers which are better adapted to flat land habitat.  Eastern timber rattlers prefer rocky deciduous woods where they can seek thermal refuge under crevices between boulders and the ground, while pygmies and diamondbacks seek out gopher tortoise and rodent burrows.

Timber Rattlesnake Crotalus horridus, Pennsylvania, Gravid females basking - Stock Image

Eastern timber rattlers (and copperheads?) in an hibernaculum.

Eastern timber rattlesnake range map.  During the mid-Pleistocene they lived in peninsular Florida but have failed to recolonize this region following interglacial sea level rise.

The Eastern diamondback rattlesnake is the largest species of crotalus.

Eastern diamondback range map.

Sistrurus miliarius barbouri

Pygmy rattlesnakes reach a length of only 2 feet long.

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Pygmy rattlesnake range map.

There are many species of interesting western rattlesnakes including the prairie, sidewinder, Mojave, and Mexican small-headed.  The genes of the latter species (C. intermedius) reveal a past history of alternating isolation and reunion between populations.  Currently, populations of Mexican small-headed rattlesnakes and closely related species are isolated from each other by desert.  They inhabit pine/oak montane forests at high elevations.  But during Ice Ages the pine/oak forests expand into the desert and populations isolated during interglacials reconnect.

The composition of rattlesnake venom varies regionally and evolves over time in response to environmental changes and evolving defense adaptations among prey species.  An environment that changes from one with an abundance of prey to one of scarcity may lead to rattlesnakes with more potent venom.  Rattlesnake venom has a slew of toxins that can damage nerves, muscles, and blood.  This makes it difficult to manufacture anti-venom that will work.

References:

Bryson, Robert

“Ephemeral Pleistocene Woodlands Connect the Dots for Highland Rattlesnakes of the Crotalus intermedius Group”

Journal of Biogeography 2011

Murphy, Robert et. al.

“Phylogeny of the Rattlesnakes (Crotalus and Sistrurus) Inferred from Sequences of Fine Mitochondrial DNA Genes”

Biology of the Vipers 2002

 

Pleistocene Cricket Frogs (Acris sp.)

April 25, 2016

Every year, trillions of horny cricket frogs call to each other along the shores of ponds and slow moving streams wherever emergent vegetation grows. ( https://www.youtube.com/watch?v=QQirydJRs7Q )This is an ancient sound of nature.  Many mighty mastodons heard these mating calls, and the small frogs occasionally were forced to jump, barely avoiding the heavy steps of the lumbering giants.  The 2 far different species shared a preference for the same kinds of wetland environments.  Old beaver ponds in the process of succeeding to wet meadows hosted the highest density of mastodons and cricket frogs.  The beavers and mastodons opened the forest canopy allowing sunlight to reach plant growth along the pond margins–ideal hiding spots for cricket frogs.  The seemingly insignificant cricket frogs outlasted the more spectacular mastodons because they are capable of reproducing at a much faster rate.

Despite their annual abundance throughout North America for well over 5 million years, cricket frogs are recorded from just 10 fossil sites.  According to the paleobiology database, the bones of cricket frogs have been identified from 4 sites in Texas, 2 in Nebraska, 2 in Kansas, 1 in Colorado, and 1 in Florida.  Their remains are associated with Miocene fauna (25 million years BP- 5 million years BP) at 3 of the sites, suggesting cricket frogs have been around for quite some time.  The amount of known fossil material for this genus compared with how many individuals lived during each generation is astonishingly low and is yet another example of how incomplete the fossil record can be.

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Southern cricket frog (A. gryllus).  They also come in a green phase with a stripe down their back.

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Pine pollen washed into the pond just in time for the season’s first hatching of tadpoles.  I wonder if the tadpoles feed on the protein rich plant food.  I have seen ducks eating pine pollen.

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During late March pond margins in Georgia are filled with cricket frog tadpoles.  Click to enlarge.

There are 3 species of cricket frogs in the Acris genus: the southern cricket frog (Acris gryllus), the northern cricket frog (A. crepitans), and Blanchard’s cricket frog (A. blanchardi).  Until recently, some taxonomists regarded these as 3 subspecies of the same species, but a study of cricket frog genetics determined there are species level differences between them.  The southern cricket frog ranges on the coastal plain of southeastern North America; the northern cricket frog occurs from the piedmont region north to southern Canada.  Blanchard’s cricket frog lives west of the Mississippi River, excepting 2 counties in Mississippi.  This grand river serves as a barrier to the flow of genes, resulting in speciation among cricket frogs, spiny lizards, rat snakes, shrews, and some species of fish.

The cricket frogs belong to the tree frog family (Hylidae), but their ancestors left the trees and inhabited pond margins instead.  The adults eat insects, but during the tadpole stage, they primarily subsist on algae.  I hypothesize cricket frog tadpoles feed on protein rich pine pollen.  The tadpoles seem most abundant when pollen washes into ponds in early spring.  A diet that includes pollen may increase the rate of tadpole growth and development, improving the odds of surviving to adulthood.  It would be interesting to test this hypothesis.  Southern cricket frogs do breed year round, but there is a peak during spring and a slow down during winter.

Herons take a heavy toll of tadpoles and adults when they swarm near shore, and the frogs often fall prey to bass and catfish when the jump in the water to avoid the long-legged birds.  Cricket frogs survive by constantly breeding, producing more frog than predators can catch and eat.

Reference:

Gamble, Tony; et. al.

“Species Limits and the Phylogeography of North American Cricket Frogs (Acris: Hylidae)”

Molecular Phylogenetics and Evolution 2008

Gavialosuchus americanus

April 14, 2016

The false gharials, a type of crocodylian, were widespread throughout the world during the Miocene between 25 million years BP- 5 million years BP.  They inhabited the coastal regions of Eurasia, and North and Central America when worldwide climate was warmer than it is today.  With their long snouts and rows of sharp teeth, they were well adapted for catching the fish that abounded in salt marshes and saltwater lagoons.  Fossil evidence of false gharials has been found along the eastern seaboard of North America from Florida to as far north as New Jersey.  Gaviolosuchus americanus is the species that lived in eastern North America during the late Miocene, while G. carolinensis occurred here during the Oligocene (33 million years BP- 25 million years BP).  The false gharials likely arose as early as the Eocene.

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Skeleton of Gavialosuchus carolinensis on display at the Charleston Museum.  This species lived during the Oligocene.

Gavialosuchus americanus Skull

Skull of Gavialosuchus americanus.  Note the long snout.

Some scientists use the scientific name of Thecachampus americanus instead of Gavialosuchus americanus.  Scientific nomenclature is a tedious topic, so I won’t delve too deeply into it on my blog.  The first scientific name ever given to a species holds precedence.  Paleontologists often find fossil material they mistakenly think is from a new species, and they will give it a name.  Later studies then determine the “new” species is actually the same as a species that had already been named.  The older species name is accepted as the correct one.  The dispute between the usage of Gavialosuchus americanus and Thecachampus americanus has yet to be unanimously resolved.

Gavialosuchus americanus was a little larger than the sole surviving species of false gharial–Tomistoma schlegeli.  The extinct species grew to 18 feet, surpassing T. schlegeli by a couple of feet.  T. schlegeli survives today in parts of Malaysia and Indonesia, but they’ve been extirpated from Thailand.  They mostly eat fish but will opportunistically take monkeys, deer, birds, other reptiles, and humans.

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The only species of false gharial still extant–Tomistoma shlegeli.  Various species  of false gharials occurred along the coasts  of Eurasia and North America  from the late Eocene to the early Pliocene.

Anatomical studies suggested the false gharials are distantly related to the true gharial (Gaviatis gangetives) of India.   The long narrow snout of the false gharial was considered an example of convergent evolution when unrelated or distantly related organisms evolve the same adaptation to similar environments.  However, a genetic study determined the false gharial and the true gharial are closely related sister species.  The vertebrate zoologists were wrong.

Gavialosuchus americanus co-existed with a species of alligator in North America.  An analysis of chemical isotopes in the bones of both crocodylians suggests they occupied different habitats.  The false gharial of America inhabited saltwater environments and alligators ruled the freshwater lakes and streams.

References:

Harshman, J. ; et. al.

“True and False Gharials: A Nuclear Genophylogeny of Crocodylians”

Systematic Biology 2003

Whiting, Evan; David Steadman, and John Krigbow

“Paleoecology of Miocene Crocodylians in Florida: Insights from Stable Isotope Analysis”

Paleogeography, Paleoclimatology, Paleoecology March 2016

The Presence of the Extinct Pleistocene Giant Tortoises (Hesperotestudo sp.) is Evidence of Open Environments but not of Warmer than Present Day Climates

January 13, 2016

The extinct giant tortoises of North America are the most poorly studied species of Pleistocene megafauna.  A google search of the largest species–Hesperotestudo crassicutata–yields a blog article I wrote several years ago as the top result.  As far as I can determine, there has been no original research of the Hesperotestudo genus in the past 15 years.  I am unaware of any scientist who currently focuses their research on the Hesperotestudo genus.  The 2 foremost experts on this genus–the late William Auffenberg and the late Claude Hibbard–have been dead for decades.  It’s a shame few researchers are studying the paleoecology of these tortoises because they were probably keystone species as important as mammoths and mastodons in shaping the landscapes where they lived.

There were 2 species of tortoises in the Hesperotestudo genus living in southeastern North America during the Pleistocene–H. crassicutata, a large species, and H. incisa, a species intermediate in size between H. crassicutata and the extant gopher tortoise (Gopherus polyphemus).  The Hesperotestudo genus is considered to be in the same monophyletic clade as the gopher tortoise.  In 1960 Claude Hibbard wrote the presence of giant tortoises in the fossil record indicated mostly frost free climates.  He believed their presence meant warmer than present day climates in the southeast…during the Ice Ages.  His assumption has been repeated in dozens if not hundreds of scientific papers without question.  I challenge this assumption, and as far as I know, I’m the only person who does.  I believe tortoises in the Hesperotestudo genus burrowed in the ground and could escape freezing temperatures by retreating into their burrows.  William Auffenberg referred to these tortoises as “non-burrowing,” but he never conducted an anatomical study to determine whether or not they could burrow into the ground.  No one has.  (Please email me if I’ve missed something in my research.)  The gopher tortoise, the closest living relative of the Hesperotestudo tortoises, digs extensive burrow systems.  Therefore, it’s a better assumption to hypothesize the Hesperotestudo tortoises did as well.  Hibbard and Auffenberg thought the Hesperotestudo tortoises were too large to dig burrows.  Recently, a reader of my blog alerted me to an African species of tortoise, Geochelone sulcata, that weighs up to 200 pounds.  This species does dig burrows, proving that size is not an obstacle to digging burrows.  The African spurred tortoise uses burrows to escape from the heat of the desert sun rather than frosts which don’t occur in the region where they live.

African spurred tortoise at burrow entrance

The African spurred tortoise digs extensive burrows to escape temperature extremes.  I propose the extinct American giant tortoises (Hesperotestudo sp.) also dug burrows and could use them to survive freezing temperatures.

During the Pleistocene climate changed much more rapidly than it has since the beginning of the Holocene ~10,000 BP.  Frequent frosts must have struck the south during the coldest climate cycles.  The Hesperotestudo line of tortoises could not have avoided extinction for millions of years, if they were incapable of surviving freezing temperatures.  I just do not accept Hibbard’s weak assumption.  Moreover, giant tortoises probably also made use of burrows dug by ground sloths and pampatheres.  Their burrows dotted the landscape as well.  (See: https://markgelbart.wordpress.com/2012/10/10/some-giant-ground-sloths-dug-long-burrows/ )

The presence of giant tortoises does indicate the existence of open environments.  Giant tortoises eat the kinds of forbs and other plants that grow in sunny conditions. They were more common on the coastal plain where a combination of fire, hurricane winds, megafauna foraging, and xeric soils contributed to open forest canopies.  However, fossil evidence of H. crassicutata has been found as far north as Bartow County, Georgia; suggesting pockets of open habitat extended into the ridge and valley region of the Appalachians.  Apparently, a jaguar gnawed on the tortoise bones which were found at Ladds.

Numerous other species of vertebrates and invertebrates made use of giant tortoise burrows.  The tortoises undoubtedly influenced the composition of plants in the environment by consuming some species, avoiding others, and perhaps spreading seeds in their dung.  Their tunnels aerated the soil and influenced the character of the landscape.

Giant tortoises favored drier environments within their range because this is where the forest canopy would have been more open.  This preference explains why so many different species of giant tortoises colonized islands far into the sea.  Beach habitats resemble desert scrub due the dearth of fresh water.  Giant tortoises inhabiting xeric beach habitats were at risk to be swept out to sea during storms.  But they float and have the ability with their slow metabolism to survive long periods without food or fresh water.  For a while during the Pleistocene a tortoise from the Hesperotestudo genus (H. burmudae) lived on Bermuda.  Bermuda was a much larger island during the low sea levels of Ice Ages, and the North American continent was closer because dry land extended onto the continental shelf.  H. burmudae colonized the island after some individuals floated out to sea following some storm event(s) during the low sea levels of an Ice Age.  H. burmudae became extinct when sea level rose and inundated its favored habitat during an interglacial 300,000 years ago.  Overhunting by man is the most likely reason the 2 continental species became extinct.

Reference:

Meyland and Steyer

“Hesperotestudo (Testudines: Tetudonidae from the Pleistocene of Bermuda, with comments on the phylogenetic position of the genus”

Zoological Journal of the Linnean Society 2000

An Alligator Bellowing at Phinizy Swamp Nature Park, Augusta, Georgia

December 28, 2015

I live a short distance from the Phinizy Swamp Natural Area. I can hop in the car and get there in 15 minutes by driving on a back road behind a few factories.  The entrance is next to the Augusta Municipal Airport.  If I didn’t have to take care of my disabled wife, I would visit Phinizy Swamp at least once a week.  But I don’t want to leave my wife in the car by herself that often, especially during summer when temperatures are uncomfortable.  Last week, on a pleasant Sunday afternoon, I decided it was the right time to look for winter migrant ducks at the swamp.  I left Anita in the car with her crochet, and my daughter and I hiked the trail that leads to an elevated boardwalk encircling a retention pond.  A surprise awaited us.

We heard a loud splash about 3 feet from where my daughter was walking.  I knew immediately that she had almost stepped on an alligator.  Augusta, Georgia is close to the northern limit of the American alligator’s range, but I didn’t realize there were any in this nature park.  We walked to the other side of the pond and heard the alligator bellow.  I’ve seen alligators on many occasions, but this was the first time I’d ever heard one bellow.  Alligators bellow during the mating season, and they also bellow to establish their territory.  Perhaps this alligator was telling us this was his pond.

On this blog I often lament the passing of the Pleistocene megafauna, so I must report that hearing the bellow of an extant species of megafauna makes me feel better…even thrills me.

Here’s audio/video from youtube of an alligator bellowing in the Okefenokee Swamp. https://www.youtube.com/watch?v=LGyId1LMTnY

The bellowing of an alligator didn’t thrill John Lawson, the first European naturalist to settle in southeastern North America (See: https://markgelbart.wordpress.com/2012/07/27/john-lawsons-voyage-to-carolina-1700-1711/ ) He inadvertently built his house (it was probably little more than a wilderness cabin) on top of an alligator den.  I just love his account of his experience.

I was pretty much frightened with one of these once; which happened thus: I had built a house about a half a mile from an Indian town, on the Fork of the Neus River, where I dwelt by myself, excepting a young Indian fellow, and a Bull-dog, that I had along with me.  I had not then been so long a Sojourner in America, as to be throughly acquainted with this Creature.  One of them had got his Nest directly under my House, which stood on high Land, and by a Creek-side, in whose banks his Entring-place was, his Den reaching the Ground directly on which my house stood, I was sitting alone by the Fire-side (about nine a Clock at Night, some time in March) the Indian fellow being gone to the Town, to see his Relations; so that there was no body in the House, but my self and my Dog; when all of a sudden, this ill-favoured Neighbor of mine, set up such a Roaring, that he made the House shake about my Ears, and so continued, like a Bittern, (but a hundred times louder, if possible) for four or five times.  The Dog stared, as if he was frightened out of his Senses; nor indeed, could I imagine what it was , having never heard one of them before.  Immediately again I had another Lesson; and so a third.  Being at the time amongst none but Savages, I began to suspect, they were working some Piece of conjuration under my house, to get away my Goods; not but that, at another time, I have as little Faith in their, or any others working miracles, by diabolic means as any person living.  At last my man came in, to whom when I had told the Story, he laugh’d at me, and presently undeceived me, by telling me what it was that made that Noise.”

I also saw the migrant ducks I hoped to encounter, though they made it difficult for me to visually identify them.  Every time I stopped to take a photo with my new camera, they ran on top of the water and swam in the opposite direction, tantalizingly just far away that I couldn’t positively identify which species they were.  My new camera has a telephoto lens, but I didn’t know exactly what I was doing the first time I used it.  I’m fairly certain I saw black ducks, pintails, female common mergansers, and goldeneyes.  Cinnamon teal may have been present…most of the ducks were brown.  Wading birds included great egrets and an immature white ibis.

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Cormorant.

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An immature white ibis.

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I think these are pintail ducks.  There were many species of migratory ducks here, but they wouldn’t cooperate and swam away when I tried to take a photo.  This was the first time I used this camera and didn’t realize I could have zoomed in even more.

Humans Co-occurred with Real Dragons (Varanus sp.) in Pleistocene Australia

August 28, 2015

Giant monitor lizards roamed Australia during the Pleistocene.  Scientists are aware of 3 species of giant lizards that lived in Australia: the Komodo dragon (Varanus komodensis), a larger undescribed species, and megalania (Varanus priscus).  Komodo dragons still occur as a relic species confined to a remote island owned by Indonesia.  They grow to 6 feet long and have a venomous bite.  The undescribed species is poorly known from just 1 fossil site. Megalania is an extinct species that grew to over 20 feet long and also had a venomous bite.  Megalania remains have been excavated from 5 sites–Wyandotte, Cuddie Springs, Darling Down, Lake Eyre basin, and Colosseum Chamber.  Archaeologists are interested in knowing whether humans overlapped in time with megalania.  Humans arrived in Australia about 50,000 years ago.  The megalania remains from Cuddie Springs and Wyandotte may be less than 50,000 years old, but the dating at these sites is considered unreliable.  Now for the first time, scientists have found remains of giant lizards that unequivocally overlapped in time with humans.

Photo: Capricorn Caves

Photo taken inside the Capricorn Cave System, Australia.  The Colosseum Chamber, where the youngest reliably dated remains of a giant monitor lizard were found, is part of this cave system.

The last 0.5Ma

The Capricorn Cave system is located near Mt. Etna.

Size comparison between human and megalania, the extinct giant lizard that roamed Australia until humans colonized the continent.

Scientists excavated a bony osteoderm of a giant lizard from a cave deposit inside Colosseum Chamber.  This hard skin plate could’ve belonged to any of the 3 species of giant monitor lizards mentioned above, but was 4x larger than the osteoderm of the largest species of monitor lizard found in Australia today.  Komodo dragon remains are not known from Australian sites younger than the mid-Pleistocene, so this specimen likely belonged to 1 of the even larger species of Varanus lizards.  Most of the fossil remains in this cave deposit consist of owl prey–the inside of the cave served as an owl’s roost for thousands of years.  But bones of kangaroos and wallabies are mixed with the ancient owl pellets.  Scientists used carbon dating of charcoal and uranium-thorium dating of straw stalactites to estimate an absolute age for the level of the deposit where the giant lizard specimen was found.  The age of the deposit ranges between 51,000 BP-30,000 BP.  The giant lizard skin plate was found closer to the deeper older level of the deposit.

Although the temporal co-occurrence of humans and giant lizards in Australia doesn’t prove humans were responsible for the extinction of megalania, it shows overhunting by or competition with humans can’t be ruled out.   I have no doubt humans were the cause of megalania’s extinction.  Megalania existed for millions of years, yet didn’t become extinct until man arrived on the continent.  This species survived dozens of dramatic climatic changes, but they didn’t become extinct until man shows up.  That can’t be coincidence.

Environmental changes resulting from Ice Age aridity may have made it more likely that humans came into conflict with giant lizards.  I hypothesize that during mid-Pleistocene arid climate cycles, megalania outcompeted Komodo dragons for dwindling resources, explaining why there are no certain remains of Komodo dragons younger than 283,000 BP in Australia.  However, during the late Pleistocene when environmental conditions deteriorated, this time humans outcompeted megalania for the dwindling resources.  Moreover, megalania feared nothing–a disastrous behavior pattern for a large animal when confronted by men with projectile weapons.

Hominids did co-exist with Komodo dragons for 900,000 years in the region of what today is Indonesia.  These islands are lush and surrounded by abundant seafood.  Humans had no need to hunt big lizards for food here.  But the interior of Australia, especially during dry climate stages, was an harsh environment where humans were forced to hunt giant lizards for food.  Australian aborigines were the real dragon hunters.  A few men with atlatls could’ve easily dispatched the former top predators of Australia.  But I’m sure some people were killed and eaten by giant lizards before the real life dragons were eradicated from the land.

Reference:

Gilbert, Price; et.al.

“Temporal Overlap of Humans and Giant Lizards (Varanidae; Squamata) in Pleistocene Australia”

Quaternary Science Reviews October 2015

Extralimital Species of Pleistocene-aged Turtle Remains Found in the Upper Coastal Plain of Alabama

August 21, 2015

George Phillips wrote his Masters Thesis about Pleistocene-aged, non-mammalian, vertebrate remains found in creeks that flow through the Alabama and Mississippi upper coastal plain, a region also known as the Black Prairie.  Turtle shells are by far the most abundant remains found here because of preservational bias.  Turtle shells are very durable, helping protect the reptile while they are alive.  This durability also makes turtle shells more likely to survive the ravages of time when the bones of most other vertebrates disintegrate.  The results of his study show that several species of turtles have experienced interesting range redistributions since the end of the Ice Age.

Map of Alabama highlighting Dallas County

Dallas County, Alabama.  Bogue Chitto Creek, located in this county, yields many Pleistocene fossil remains.

Blanding’s turtle (Emboidia blandingii) is an endangered species presently restricted to the upper Midwest and parts of New England.  Most of this species’ present day range was under glacial ice during the Ice Age and thus uninhabitable.  Remains of Blanding’s turtle can be found in Pleistocene deposits as far south as the Black Prairie region in Alabama.  The presence of this species in Alabama suggests much cooler summers in the south during the Ice Age (though winters may have been as mild or just a little cooler than those of today). Blanding’s turtles may be unable to endure the long hot summers of the present day south, and this may be the limiting factor on their range today.

Blanding’s Turtle occurred in Alabama during the Ice Age but no longer ranges this far south.

Map of Blanding's Turtle

Present day range of Blanding’s turtle.  During the Ice Age about 70% of this territory was under glacial ice.

The wood turtle (Glyptemys insculpta) is another species of turtle with northern affinities that lived in Alabama (and other parts of the south) during the Ice Age.  This species may also be unable to survive long hot summers.

Plastron of an adult male.

Wood turtle.

Present day range map of the wood turtle.  During the Ice Age >90% of this range was under glacial ice and this species retreated south.  Longer hotter summers chased them back up north.

The only known Pleistocene-aged specimen of a musk turtle (Sternotherus carianitus) was found in Catalpa Creek, Alabama. Today, this species occurs to the west of this site.  Its rarity in the fossil record is unexplained and is probably just due to chance.  During the Pleistocene it apparently ranged further east than it does today.  Any number of unknown reasons could explain its extirpation from the most eastern parts of its range–disease, excessive egg predation, or competition with other species of turtles.

File:Carapace Sternotherus carinatus.JPG

Musk turtle.

Present day range map for musk turtle.  They formerly ranged a little further east during the Pleistocene.

There are 3 species of red-bellied turtles.  The Florida red-bellied turtle (Pseudemys concinna) is presently restricted to peninsular Florida, but Pleistocene-aged remains of this species have been found in Bartow County located in north Georgia.  The Alabama red bellied turtle (Pseudemys alabamensis) is presently restricted to extreme southern Alabama and Mississippi.  The red bellied turtle (P. rubriventris) is presently restricted to the mid-Atlantic states, but Pleistocene -aged remains of this species have been found in the upper coastal plain of Alabama.  It’s likely these 3 species of red-bellied turtles diverged from 1 continuous population that existed before the Pleistocene-Holocene transition when for some unknown reason they became geographically isolated into their present day ranges.  Their curious range distributions beg for a study of their molecular DNA.  The 3 present day species represent a speciation event that may have occurred as recently as 10,000 years ago.  I can’t determine why red-bellied turtles were extirpated from regions in between their present day ranges.  Did overharvesting by humans play a role?

Present day range map for the mid-Atlantic red-bellied turtle (Pseudemys rubriventris)  Remains of this species have been identified from Alabama.

Range map for Alabama red-bellied turtle.  The Pleistocene/Holocene transition was likely a speciation event that caused the 3 species of red-bellied turtles to diverge.

An extinct Pleistocene subspecies of box turtle (Terapene Carolina putnami) was common in Alabama’s coastal plain.  It was larger than present day box turtles but otherwise was similar.  There is no direct evidence of gopher tortoises (Gopherus polyphemus) from the Black Prairie region during the Pleistocene, but a Pleistocene-aged specimen of an indigo snake was found in Bogue Chitto Creek located about 40 miles north of the present day range of this tortoise.  Indigo snakes depend upon gopher tortoise burrows for shelter, so the presence of this snake suggests the presence of gopher tortoises nearby.  Gopher tortoises require sandy soils for burrowing.  They don’t burrow in the heavy upland clay soils so widespread in this region, but they may have burrowed in the alluvial (streamside) sands by the creek.  Gopher tortoises require open environments where they can feed upon short sun-loving plants.  The closure of the forest canopy would have caused their extirpation here.

Two scutes of the extinct giant tortoise (Hesperotestudo crassicutata) were found in this region.  Scientists puzzle over the co-existence here of the cold adapted wood turtle and Blanding’s turtle with the giant tortoise, a species they assume required a frost free environment.  I disagree with their assumption.  I hypothesize giant tortoises were capable of surviving freezing temperatures by either burrowing underground, like their closest living relative (the gopher tortoise), or by utilizing burrows dug by giant ground sloths. If giant tortoises could survive mild frosts as I believe, this species could have co-existed in the same region as cold-adapted species of turtles.  However, it’s just as likely their remains represent a warm climate phase, temporally distinct from when wood turtles and Blanding’s turtles roamed the creek bottoms.  As far as I know, none of these specimens has been radio-carbon dated.

Species of turtle remains found in Pleistocene deposits here that still occur in the region include snapping turtle, alligator snapping turtle, spiny softshell, stinkpot, painted, slider, and Alabama map turtles.

Reference:

Phillips, George

“Paleofaunistics of Non-mammalian Vertebrates from the Late Pleistocene of the Mississippi Black Prairie”

North Carolina State Masters Thesis 2006

Snake Island, Brazil

August 12, 2015

Rising sea levels can cause speciation (the evolution of new species) by geographically isolating populations.  A small rocky island off the coast of Brazil is home to a perfect example of this.  Genetic evidence suggests the golden lancehead viper (Bothrops insularis) diverged from the jaracara (B. jaracara) approximately 2 million years ago when sea level rise isolated Snake Island from the rest of South America.  The ancestral population of snakes that became stranded on this island evolved different characteristics than the jaracara, a species that is widespread throughout the mainland of eastern South America.  Jaracaras primarily feed upon rodents, birds, and lizards; but there are no rodents on Snake Island.   Resident birds co-exist with the high density of snakes on this island.  The birds that live on this small island quickly learn to be wary and avoid snake predation.  So golden lanceheads depend heavily upon naïve transient birds that are just visiting the island.  Golden lanceheads evolved more potent venom, shorter fangs, and longer heads.  The more potent venom kills the birds faster, and the shorter fangs are less likely to break when the golden lanceheads hang on to a struggling bird.  By contrast jaracaras strike, release, and wait for their prey to die; thus avoiding injury.  The longer head on the golden lancehead allows them to switch to larger prey at an earlier age than a jaracara.  Golden lanceheads grow to almost 4 feet long, over a foot less than jaracaras.  The smaller size means they require less food.  They do also take lizards and other lanceheads.

Location of the island just off the coast of Brazil

Location of Snake Island.

Snake Island.

 

 

 

 

 

 

 

 

 

The golden lancehead snake (Bothrops insularis.)  Beautiful snake.

Jaracara (B. jaracara).  Genetic studies suggest golden lance heads evolved from this species about 2 million years ago when sea level rise isolated them from the parent population on Snake Island.  The fer-de-lance also belongs to this genus.

There are 37 species of snakes in the Bothrops genus, and all live in South America.  Every species has potent venom, but the golden lancehead’s venom is 5x more potent than that of the jaracara.  The venom causes extensive tissue damage.  People bitten by these vipers sometimes require amputation, but antivenin has reduced the rate of death.  Marlin Perkins of Wild Kingdom fame was bitten by venomous snakes several times during his career.  He wrote the only good thing about getting bitten by a venomous snake was that after the effects dissipated, he recovered completely.  There is no evidence a human has ever been bitten by a golden lancehead.  A legend that a lighthouse keeper and his family were killed by golden lanceheads in 1920 has never been confirmed.  There are 200 golden lanceheads on Snake Island.  They exist in the wild nowhere else in the world.

Reference:

Wuster, Wolfgang; et. al.

“Morphological Correlates of Incipient Arboreality and Ornithophagy in Island Pit Vipers and the Phylogenetic Position of Bothrops insularis”

Journal of Zoology 2005

The Pleistocene Ridge and Valley Reptile Corridor

April 28, 2015

The composition of reptile and amphibian species living in present day Georgia is almost the same as it was during the late Pleistocene.  This suggests climate change in southeastern North America has been much more moderate compared to the rest of the continent.  There are 2 excellent late Pleistocene fossil sites in the ridge and valley region of Georgia that yield the remains of reptiles and amphibians–Ladds Quarry and Kingston Saltpeter Cave.  Over 40 species of reptiles and amphibians (aka herpetofauna) were excavated from Kingston Saltpeter Cave, and all but 1 (wood turtle) still live in the region.  Most of the herpetofaunal remains recovered from Ladds also still live in Georgia, but there are a few exceptions, leading to some interesting paleoecological implications for this time period.

Map of sites sampled in the Valley and Ridge of Alabama and Georgia to assess responses of fish, invertebrates, and algae to urbanization.

Map of the ridge and valley region of Georgia and Alabama.  This region provided a corridor where reptiles and amphibians with northern affinities could mingle with those that preferred a warmer climate.

Fox snakes (Elaphe vulpine) and wood turtles (Glyptemys insculpta) lived in the ridge and valley region of Georgia about 13,000 years ago.  These 2 species no longer live this far south, implying summers were cooler here then.  However, the extinct giant tortoise (Hesperotestudo crassicutata), red bellied turtles (Pseudemys nelsoni), and southern toads (Bufo terrestris) ranged into the ridge and valley region as well.  Researchers assume giant tortoises required frost free winters, while red bellied turtles no longer occur north of the Okefenokee Swamp.  Aside from a disjunct population, southern toads are restricted to the coastal plain.  The presence of these 3 species implies a climate phase of warmer winters than those of the present.  There is an astronomical explanation for the strange co-existence of species with northern affinities alongside those of warmer preferences.

The fossil remains that accumulated at both Ladds and the Kingston Cave date to the Boling-Alerod Interstadial when average annual temperatures spiked from Ice Age lows to nearly modern day warm temperatures. (Pundits who claim today’s rate of global warming is “unprecedented” are ignorant of this climate phase.)  The Boling-Alerod lasted from 15,000 BP-12,900 BP.  This warm pulse led to rapid melting of the glaciers covering Canada then.  Although average annual temperatures were similar to those of today, they were not distributed in the same way.  Summer highs were lower on average than they are today, but winter low temperatures in this region probably did not go far below freezing.  During the Boling-Alerod Interstadial, the earth tilted to a lesser degree than it does today, resulting in reduced seasonality. It’s fascinating how small changes in astronomy can be tied to changes in the distribution of small animals.

I disagree with scientists who believe the ridge and valley was entirely frost free then.  I hypothesize the extinct giant tortoise was able to survive light frosts by digging burrows or by using burrows dug by ground sloths and pampatheres. (See: https://markgelbart.wordpress.com/2011/04/15/the-extinct-pleistocene-giant-tortoise-hesperotestudo-crassicutata-must-have-been-able-to-survive-light-frosts/)  Moreover, red bellied turtles and southern toads do live in regions that experience light frosts every winter.  Instead, the ridge and valley region probably had winters similar to those of modern day south Georgia and north Florida.  Florida muskrats (Neofiber alleni) have a similar range as red-bellied turtles, and their fossil remains have also been found at Ladds.  The presence of Florida muskrats this far north during the Boling-Alerod indicates year round green vegetation and does suggest a longer growing season but does not preclude the possibility of winter frosts.

Wood Turtle

Wood turtle.  This species lived in north Georgia during the Pleistocene but no longer occurs this far south.

Florida red-bellied turtle.  This species lived in north Georgia during the Pleistocene but no longer occurs this far north.

The ridge and valley region provided a corridor for the migration of species that expanded their range according to varying climate phases.  Species not well adapted to living at higher elevations could utilize river valleys and move south to north or vice versa.  Species that preferred higher elevations could travel along the ridges, also along a north-south axis.  The Appalachicola river is thought to be another corridor that facilitated north-south  migrations of species, correlating with changes in climate phases.  I think the 2 corridors are close enough to have some connection.  Some species expanding their range up and down the Appalachicola River corridor reached the ridge and valley region and expanded their range through there as well.

The region between these 2 corridors includes Talbot, Taylor, Schley, and Marion Counties in southwest central Georgia.  Researchers recently discovered this region is a diverse herpetofaunal hotspot. In just 1 week, 25 people surveyed this region and counted 62 species of reptiles and amphibians, greater than any other region in North America north of Mexico.  This includes more reptiles than are found in Big Bend National Park, and more amphibians than are found in the Great Smoky Mountains National Park.  This region is the southernmost range limit of the wood frog (Rana sylvatica) and the spring salamander (Gyrinophata poryphactos), yet it is the most inland northern range limit for coastal plain species such as the gopher frog (Rana areolata), striped newt (Notophthalmus perstiratus)), and diamond back rattlesnake (Crotalus adamenteus).  They also found an endangered alligator snapping turtle (Macroclemys temmincki), and gopher tortoises (Gopherus polyphemus).

The southern toad has a curious disjunct population in upper South Carolina.  The scientific literature is silent as to their preferred habitat, other than their preference for sandy soils.  Most of their modern day range was formerly open pine savannah, so I assume this is their favored habitat.  This suggests at least some savannahs occurred well into the northern parts of South Carolina and Georgia.  Indians maintained extensive grassy savannahs in upstate South Carolina by setting frequent fires.  William Bartram did travel through miles of “strawberry plains” in this area circa 1777.  The extinct giant tortoise favored savannah habitat as well.  The presence of these 2 species at Ladds indicates some savannahs occurred in the ridge and valley region during the late Pleistocene.  There is a disjunct population of longleaf pine (Pinus palustris) in the ridge and valley region at Berry College.  At least some areas of longleaf pine savannah have occurred in this region since at least the Boling-Alerod Interstadial. Apparently, lightning-induced fires were frequent enough to maintain this environment, even before man began setting fires here.

Bufo terrestris

Range map for southern toad.  Note the disjunct population in northwestern Georgia and northeastern South Carolina.  Fossils of this species have been found in the ridge and valley region at Ladds, located west of this disjunct population.

Incidentally, it should not be a great surprise if fossil evidence of alligator and gopher tortoise, dating to the late Pleistocene, is some day found in the ridge and valley region.  The herpetofauna biodiversity of this region during the Boling-Alerod Interstadial likely surpassed that of any present day region of North America north of Mexico.

References:

Holman, Alan

“Paleoclimatic Implications of Pleistocene Herpetofauna of Eastern and Central North America”

National Geographic Research

Graham, Sean; et. al.

“An Overlooked Hotspot: Rapid Biodiversity Assessment Reveals a Region of Exceptional Herpetofaunal Richness in Southeastern North America”

Southeastern Naturalist 9(1) 2010