Archive for the ‘herpetology’ Category

Pterosaurs may have Cared for their Young

January 11, 2018

Some imagine the Cretaceous and Jurassic Ages as a time when the earth was strange and full of terrifying monsters.    The earth was a vast wilderness then, dangerous perhaps for most creatures, but it was no more strange or terrifying than the world we live in today–the Anthropocene with its genocides, terrorism, potential nuclear war, and extensive environmental destruction caused by a single dominant species.  The dinosaur world hosted species different from those of modern day earth, but these organisms were part of ecosystems recognizably comparable to those of today.  For example fish-eating pterosaurs nested in communal colonies, not unlike present day heron and egret rookeries.  Pterosaurs were not dinosaurs but instead were flying reptiles–the only vertebrates besides birds and bats to evolve the ability to fly. After their initial evolution the early Jurassic pterosaurs radiated into many species and occupied different ecological niches.  From the middle of the Jurassic until their extinction at the end of the Cretaceous 66 million years ago, there were probably about as many species of pterosaurs living in the world as there are birds today.  Evidence from 1 site in northwest China suggests pterosaurs, like so many modern day vertebrates, cared for their young.

Paleontologists found 215 fossilized eggs of a species of pterosaur known as Hamipterus tianshanensis, a fish-eating species that nested communally.  The fossils from this site date to about 120 million years BP, and they are from many generations. The nests were located next to a lake at the time of deposition.  Apparently, pterosaurs used this site annually.  Perhaps it was difficult for predators to access.  Some of the eggs contain visible embryos.  The embryos show well developed legs but underdeveloped wing bones.  This suggests the hatchlings couldn’t fly and depended upon parental care for food until their wings developed.  However this conclusion isn’t certain.  The fossils are of an embryonic stage, not actual hatchlings.  The wing bones may have developed at a later embryonic stage.

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Artist’s representations of pterosaurs have changed over the years.  In this old issue of Green Lantern from the early 1970s the pterosaur is larger than a man, featherless, and conveniently yellow.  Green Lantern’s power ring doesn’t work against yellow objects.  The wingspans of some species of pterosaurs were longer than the length of a man, but they could not have seized and carried a man away.  They were able to leap straight up and fly though, unlike large modern bird species which must take a running start.

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This more modern representation of pterosaurs by Masato Hattori, a depiction of Hamipterus tianshanensis, shows the reptile covered with hair-like feather structures.  It also had teeth.

Cretaceous-aged outcroppings occur near Columbus, Georgia and the Chattahoochee River.  These are the only regions in the state where Cretaceous fossils have been found.  David Schwimmer, a professor at Columbus State, excavated 3 pterosaur wing bones from an outcropping here–the only evidence pterosaurs formerly existed in the state.

References:

Deeming, Charles

“How Pterosaurs Bred”

Science 358 (6367) December 2017

Wang, Xi; et. al.

“Egg Accumulation with 3-D Embryos Provides Insights into the Life History of a Pterosaur”

Science 358 (6367) December 2017

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Alligators vs Sharks

October 15, 2017

Bloody battles between hundreds of alligators and sharks were an oddity of nature that occurred infrequently for millions of years.  Alligators are considered a freshwater species, but they do inhabit brackish lagoons and can even live in saltwater environments for weeks.  Alligators foraging near beaches normally prey on fish, shrimp, crabs, wading birds, raccoons, mink, and sea turtles.  Alligators take advantage of weather and tidal conditions that concentrate their prey in confined areas.  During the year 1877 near Jupiter, Florida a strong flood tide trapped a large number of fish in a bend of a tidal inlet, attracting an estimated 500 alligators.  The alligator feeding frenzy lasted for days, and the blood drew hundreds of sharks into the main channel of the inlet.  The current shifted and carried the alligators into the main channel where they fought sharks for hours.  Dead alligators and sharks washed ashore for days, following the battle.  It is unlikely such a spectacle could occur today.  Sharks have been overfished, greatly diminishing their population, and alligators, though on the increase, will never be as abundant as they were when Florida was mostly wilderness.  However, the primeval world was the scene of many alligator vs shark wars because they co-existed for millions of years, often competing for the same prey.  Alligators are a member of the crocodilian family.  The crocodilians evolved at least 83.5 million years ago, and the ancestors of the crocodilians, the Pseudosuchia, originated 250 million years ago.  The ancestors of the alligator’s ancestors undoubtedly came into conflict with sharks.  It’s an ancient rivalry.  Spectacular battles between large groups of alligators and sharks may no longer occur, but individual crocodilians and sharks still eat each other on occasion.

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Alligator preying on a nurse shark at the Ding Darling National Wildlife Refuge near Sanibel, Florida.  This photo is on the cover of this quarter’s Southeastern Naturalist.

An article published in this quarter’s Southeastern Naturalist collects all the known incidences of alligators preying on sharks and vice versa. On Wassaw Island, Georgia a scientist saw an alligator prey upon a bonnethead shark, and he also witnessed another alligator catch and eat a lemon shark.  A case of an alligator preying on a bonnethead took place at St. Mark, Florida as well.  Bonnetheads feed on crabs in shallow water, making them vulnerable to alligator attack.  The photo above shows an alligator preying on a nurse shark. Sharks have been recorded feeding upon bottom-dwelling southern and Atlantic stingrays, and stinging barbs are occasionally found embedded in alligators.

There are no recent incidents of known shark attacks on alligators, but there are 3 records from the late 19th century, including the account mentioned in the first paragraph.  In addition to that account a shark bit an alligator in 2 near Pilot Cove, Florida in 1884, and in 1888 5 or 6 alligators battled a similar number of sharks in the Indian River, resulting in some deaths of both.

Around the world there are numerous cases of crocodiles and sharks eating each other.  Bull sharks venture into fresh water and have been recorded falling victim to Australian salt water crocodiles.  Crocodile remains have been removed from the stomachs of tiger sharks near Australia, South Africa, and Indonesia.  Caimans filled the belly of at least 1 tiger shark off the coast of South America.

Who wins a fight between an alligator or crocodile and a shark?  It depends upon the size of the individual and who bites who first.  The larger individuals have the bigger bite and the advantage, but if they are close to the same size, the first to deliver a serious bite quickly gains the upper hand.

*Note the title of the reference below.  The dispassionate scientifically proper language amuses me to no end.  Translated into layman’s English it means alligators and sharks eating each other.

Reference:

Nifong, James; and Russel Lowers

“Reciprocal Intraguild Predation between Alligator mississippiensis (American alligator) and Elasmobranchiii in Southeastern United States”

Southeastern Naturalist 3 (16) 2017

The Frog that ate Dinosaurs

September 28, 2017

The horned frogs of South America are often called pacman frogs because they can swallow prey as large as themselves.  Unlike all other frogs and toads, they bite and have powerful jaws attached to sturdy skulls.  Horned frogs (Ceratophys cranwelli) are probably related to an extinct frog (Beezelebufo ampinga) that lived on Madagascar during the late Cretaceous.  The anatomy between these species is similar.  Moreover, during the Cretaceous Madagascar, Africa, Antarctica, and South America were 1 continent; so a close evolutionary relationship makes sense.  Beezelebufo was much larger than extant horned frogs, reaching a weight of at least 9 pounds.  The largest living frog in the world today is the goliath frog (Conrauo goliath) of Africa, and it grows to just 7 pounds.  But Beezelebufo had a much more powerful bite.

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Beelzebufo was big enough to eat dinosaur hatchlings.

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The goliath frog is the largest living species of frog in the world.  Beelzebufo was over 20% larger.

Scientists measured the bite force of modern day horned frogs and used this to extrapolate the bite force of beezelebufo.  They estimated beezelebufo could bite as hard as a lion or tiger and harder than a wolf.  They could also bite harder than juvenile crocodilians of the same size.  Available fossil material of beezelebufo consists of individuals that were still growing at the time of deposition.  If full grown adult material is discovered and used for extrapolation, it’s possible scientists will determine adult beezelebufos had an even more powerful bite.  The authors of the below referenced paper believe beezelebufo fed upon dinosaur hatchlings and juvenile crocodilians.  Most frogs use their sticky tongues to capture prey, but horned frogs and their large extinct cousin clamp (or clamped) down with their powerful jaws.

Video of a horned frog (aka pacman frog) eating a mouse.  This species is related to the extinct beezelebufo, a frog that ate dinosaurs.

Video of bullfrog stalking and eating a sparrow.  Beezelebufo probably stalked dinosaur hatchlings at water’s edge.  Frog predation on dinosaurs continues today.  Most paleontologists believe birds descend from dinosaurs and birds are just modern day versions of dinosaurs.

Reference:

Lappin, A. Christopher; et. al.

“Bite Force in the Horned Frog (Ceratophys cranwelli) with Implications for Extinct Giant Frogs”

Scientific Reports 7 2017

 

Rapid Anole (Anolis carolinensis) Evolution

August 21, 2017

Misinformed creationists some times ask, if evolution is true, why isn’t it happening now?  There is a simple answer to that question.  Evolution is an ongoing process, and it IS happening now.  Evidence of continuing evolution isn’t readily apparent to the non-observant eye because usually it is a slow process–evolution often requires generations of natural selection to influence the phenotypical changes that demonstrate it.  However,  scientists discovered an example of evolution that occurred within 1 generation of an anole population in south Texas.  A team of scientists had recently studied the differences in cold tolerance between the population of anoles that live in south Texas with those that live near the northern limits of their range.  The south Texas anoles lose muscular coordination when temperatures drop to about 51 degrees F, while anoles near the northern limits of their range lose coordination when temperatures reach 43 degrees F.  An unusual cold snap struck south Texas shortly after scientists gathered this data, and they took another look at this anole population.  They discovered that exposure to cold temperatures changed the DNA of south Texas anoles.  4 genomic regions, especially those related to nervous system function, changed.  The lizards had rapidly evolved the ability to retain muscle coordination at lower temperatures, and they will pass these genetic changes on to the next generation.  This is a perfect example of evolution, defined as the change over time in the genetic characteristics of a population.  Most creationists can’t even define evolution.  They reject the fundamental basis of all biological science because it interferes with their belief in the supernatural.  Let’s see them try to deny this case study.

Anole characteristic threat display.

Anoles are a successful and rapidly evolving species. Some populations have adapted to city living, having evolved stickier toe pads that enable them to climb window glass.  In Florida the brown Cuban anole was accidentally introduced.  They occupy the same niche as the American anole.  In areas colonized by this alien anole, native anoles evolved larger toes that allow them to climb thinner branches.  This occurred in less than 15 years (20 generations for anoles living in Florida).  So now, areas with both species of anoles have a niche partition–Cuban anoles occupy lower branches, while native anoles live in the tree tops.

Worldwide, there are 391 species of anoles, but 9 are closely related to the species (A. carolinensis) that is widespread in the southeastern U.S.  Genetic studies suggests all 9 of these species descend from a founder population originating on Cuba.  A. carolinensis diverged from western Cuban anoles about 6 million years ago.  This occurred as a rafting event when a tropical storm washed debris from Cuba to the Gulf Coast of North America.  At least 1 male and 1 female were clinging to the debris when it made landfall.  All Caribbean islands were populated by anoles originating on Cuba from similar rafting events.

Fossil evidence of anoles has been excavated from 1 site in Georgia (Ladds), 1 site in Alabama (Bell Cave), and 10 sites in Florida.  None date to older than the mid-Pleistocene, but genetic evidence indicates they’ve occurred in southeastern North America since the late Miocene.

References:

Campbell-Staten, Shane; et. al.

“Winter Storms Drive Rapid Phenotype, Regulation, and Genome Shift in the Green Anole Lizard”

Science August 4, 2017

Glor, Richard; J. Losos, A. Larso

“Out of Cuba: Overwater Dispersal and Speciation Among Lizards in the Anolis subgroup”

Molecular Ecology 14 2005

100 Species of Reptiles and Amphibians along the Altamaha River, Georgia

July 17, 2017

The corridor along the Altamaha River drainage is the best remaining wilderness in Georgia.  The land here is protected by 11 state wildlife management areas and 2 private landowners.  The Nature Conservancy owns Moody Forest, and the Orianne Indigo Snake Society owns land that hosts the greatest variety of reptiles and amphibians in the state.  Scientists have recently begun studying this largely undeveloped corridor.  From 2008-2016 scientists conducted the first comprehensive survey of reptiles and amphibians along this river system.  They used intensive group searches, turtle traps, and drift fences to find species; and they listened for frog calls.  Drift fences are barriers interspersed with pitfall traps.  Smaller reptiles and amphibians attempt to go around the barriers and fall into the traps.  Surveyors collected an astonishing 100 species, indicating the region has the richest diversity of reptile and amphibian species in the state.  Fort Stewart army base ranks 2nd with 97 species, and the Okefenokee Swamp hosts 88 species.

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Map of the Altamaha River Drainage.  The Altamaha is fed by 3 major tributaries–the Oconee, Ocmulgee, and Ohoopee.

Scientists catalogued 59 species of reptiles and 41 species of amphibians along the Altamaha River.  This number includes 17 species that are considered endangered by the federal and/or state governments, including indigo snake, diamondback rattlesnake, southern hog-nosed snake, rainbow snake, harlequin coral snake, pine snake, pine woods litter snake, slender glass lizard, mole skink, gopher tortoise, spotted turtle, southern dusky salamander, and gopher frog.

Surprisingly, cottonmouth water moccasins were found at less than half the sites surveyed, and they were absent from the main branch of the river.  The authors of this study suggest regular flooding “scours” riverside vegetation, eliminating the cover favored by the venomous snakes.  On the other hand river cooters (Pseudemys concinna) were found to be abundant in the river, though according to the preceding scientific literature they were not known to be present here.

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River cooters are common in the main branch of the Altamaha River.  Before the below referenced survey was conducted, reptiles and amphibians along this river were so little studied, this species was unrecorded in the scientific literature as living in the river.

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Red salamanders (Pseudotriton ruber) reach the southeasternmost limit of their range at the Altamaha River.  This waterway is a geographical barrier for 14 species of reptiles and amphibians.

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The pine woods litter snake (Rhadinia flavilata) reaches the northern limit of its range at the Altamaha River.  This species grows to about 1 foot in length and mostly lives underground.  They are venomous but have rear fangs that are probably unable to break human skin.  They feed on small reptiles and amphibians and are no danger to people.

The reason such a high diversity of species occurs along the Altamaha River is the great variety of habitats.  The corridor hosts open water, bottomland hardwoods, cypress/tupelo swamps, longleaf pine savannahs, sandhills, Carolina Bays, and muddy seepage areas at the bottom of north-facing slopes.  However, the river itself serves as a barrier blocking movement of some species’ populations.  The Altamaha River is the southeasternmost range limit for 13 species, and the northernmost range limit for 1 species.

The high number of reptile and amphibian species is evidence the region of the Altamaha River has been climatically stable for millions of years.  The vicissitudes of Pleistocene climate fluctuations were muted here.  During cold arid stadials swampy wetlands shrunk in size but persisted as relics, while savannahs and scrubby sandhill habitat expanded.  Currently, wetland habitat has expanded but before European settlement grassland and scrub habitat were still extensive.  Western Georgia and Alabama have also experience long term climatic stability.  (See:

https://markgelbart.wordpress.com/2015/04/28/the-pleistocene-ridge-and-valley-reptile-corridor/

https://markgelbart.wordpress.com/2015/08/21/extralimital-species-of-pleistocene-aged-turtle-remains-found-in-the-upper-coastal-plain-of-alabama/

)  Like the black prairie region of Alabama, the Altamaha river also undoubtedly served as a refuge for species of reptiles whose current range was obliterated by an ice sheet during Ice Ages.  Blanding’s and wood turtles may have extended their range this far south then.  Extinct giant tortoises (Hesperotestudo crassicutata and H. incisa) likely lived alongside their smaller cousin, the gopher tortoise.  But otherwise the modern species list of reptiles and amphibians in the region is mostly unchanged from the Pleistocene.

Reference:

Stevenson, Dirk, and Houston Chandler

“The Herpetofauna of Conservation Lands along the Altamaha River, Georgia”

Southeastern Naturalist 16 (2) 2017

Musk Turtles (Sternotherus odoratus) Prefer Buffalo Wings

July 12, 2017

Buffalo chicken wings exploded in popularity when the Buffalo Bills kept losing Super Bowls almost 30 years ago.  The meaty spicy snacks are the perfect drinking party food.  The heat makes a drinker thirsty, yet the fat and protein slow down absorption of alcohol.  The chicken wings are fried, then tossed in a sauce made of butter or margarine mixed with hot pepper vinegar.  Supposedly, Buffalo wings were invented by Teressa Bellissimo at Anchor Bar in Buffalo, New York during 1964.  However, Anchor Bar didn’t serve Buffalo wings until 1974.  Instead, credit for inventing the dish should probably go to John Young, a native of Alabama, who moved to Buffalo and made spicy chicken wings during 1964.  He seems the more likely originator of the dish because Buffalo wings resemble the kind of Cajun or soul food cooking that might be found in south Alabama.  Cajun and soul food cuisine make excellent use of throw away ingredients. Before the wing craze they were considered a disposable part of the bird.

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2 stinkpot (aka musk turtles) mating in Woodbridge Lake, Evans, Georgia.  Scientists discovered they prefer Buffalo chicken wings over any other bait.

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Buffalo wings–favorite bait of the stinkpot turtle.

Musk turtles (also known as stinkpots because of their smelly defense glands) like to eat Buffalo chicken wings.  Scientists studying musk turtles at Comal Springs, Texas compared the effectiveness of various kinds of baits.  Musk turtles greatly prefer Buffalo chicken wings over fried chicken, raw chicken, catfish stink bait, cat food, potted meat, and canned sardines in oil.  The experiment took place in 2 phases.  Phase 1 compared Buffalo chicken against the non-chicken baits.  Phase 2 compared the Buffalo wings against fried and raw chicken.  Scientists captured 231 musk turtles using Buffalo wings compared to just 45 using stink bait, cat food, potted meat, and sardines.  Scientists captured 46 musk turtles using Buffalo wings vs 16 with fried chicken and 10 with raw chicken.  Musk turtles, like people, are attracted to grease and spice.  Turtles agree: they taste better than their natural diet of crayfish, snails, clams, tadpoles, and insects.

Reference:

Munscher, Eric; et. al.

“A Novel Bait for Capturing Eastern Mud Turtles”

Southeastern Naturalist 16 (2) 2017

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.

New Pictures 026

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.

Tomistoma schlegelii false gharial LA zoo 03.jpg

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