Archive for the ‘herpetology’ Category

Hog-Nose Snakes–The Toad-eaters

October 1, 2021

My research on toads led me to the fascinating Heterodon genus of snakes. They specialize in preying upon toads, creatures most other predators avoid eating because the poison glands on their skin make them distasteful and even toxic. The Heterodon genus includes 3 species of hog nose snake–eastern southern, and western. They are easy to distinguish from other snakes because their nose resembles a pig’s snout. The eastern hog nose snake (Heterodon platyrhinus) occupies the largest range which partially overlaps with that of the western hog nose snake (H. nasicus) and fully overlaps the more limited range of the southern hog nose snake (H. simus).

Eastern Hog-nose snake. I’ve seen this species with this color variation in my neighborhood.
Southern hog-nose snake. They are smaller and less widespread than Eastern hog-nose snakes.
Hog-nose snake playing dead.

The eastern hog nose snake varies greatly in color. I looked for photos of this species on google images and found at least 18 different color variations. The variation of this snake in my neighborhood most closely resembles the top photo above. This species grows to almost 4 feet long and inhabits sandy soils in open woodlands. In some regions frogs and toads make up 100% of their diet, but in other regions they also prey on mice, birds, lizards, and other snakes. When threatened they feign aggression. If this doesn’t deter a predator, they play dead. Fossil evidence of this species dating to the Pleistocene and/or Pliocene have been found at Ladds in Georgia, as well as sites in Kansas, Oklahoma, Florida, Texas, and West Virginia. The Heterodon genus is at least 5 million years old.

The southern hog nose snake grows smaller than the eastern, reaching lengths of less than 2 feet. Biologists believe the population of this species is in decline, while those of the eastern are stable. Southern hog nose snakes also prefer sandy soils in open woodlands. They too feign aggression and play dead, but these actions are less pronounced than those of the eastern. Fossil specimens of this species have been found at 2 sites in Florida.

Hog nose snakes rarely bite people. An exception occurred when a man who had just handled toads picked up an hog nose snake. The snake likely scented the toad and got confused. They do have venom injected by rear fangs, but it is dangerous for amphibians, not people. Frogs and toads swell up to prevent snakes from swallowing them, however, the rear fangs of a hog nose snake puncture the frog, deflating it, and the venom stops the frog from struggling–another example of evolutionary measure and countermeasure between predator and prey.

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Pleistocene Toads

September 24, 2021

During the first months of 1976 I was the new kid at Patty Hilsman Middle School in Athens, Georgia where a group of cruel, little jerks decided to give me the nickname–toad. The nickname stuck immediately. Jocks, nerds, “cool” kids, and pretty girls all referred to me as toad instead of my given name of Mark. I was 13 years old, and the experience didn’t enhance my self-esteem. It also gave me a dim view of southern hospitality (our family had moved from Ohio), and after living in the South for over 45 years, I can confirm it is a myth. I saw a southern toad (Bufo terrestris) hopping in my yard the other day, and it brought back the unpleasant memory of being likened to an ugly amphibian. Nevertheless, it also reminded me that I’ve never written about this amazing Pleistocene survivor. Toads may seem insignificant, but they have outlasted many of the beautiful more dynamic animals that lived during the Pleistocene.

Southern toad. This species is common in my yard. Photo from Alamy.

Georgia is home to 2 species of true toads, 1 species of spadefoot toad, and 1 species of narrow-headed frog that is given the common name of toad. Southern toads are the most common species. They live in areas with sandy soils where they can burrow during the heat of the day. They hunt insects at night. After heavy rains, they breed and lay eggs in temporary pools where, if the pool doesn’t dry out, their tadpoles can metamorphize into adults. Fossil evidence of southern toads dating to the Pleistocene has been found at 6 sites in Florida and 1 site in Alabama. They were likely just as widespread then as now.

Oak toad. My neighborhood is close to the northern range limit for this species. I’ve seen small toads in my yard but they may be juvenile southern toads. Photo from pininterest.

Oak toads (Bufo quercicus) also prefer sandy soils and are common on coastal plain pine savannahs. This species is small, growing to just an inch in length. Fossil evidence of this species dating to the Pleistocene has been found at just 1 site in Florida (Reddick).

Eastern spade foot toad. They live in spiral burrows underground but emerge above ground to breed.

Eastern spade foot toads (Scaphiophus holbrooki) belong to the Pelobotidae family and are not closely related to true toads. They are named for a protuberance found on both feet that helps them dig deep spiral burrows where they spend most of their life, and for this reason they are rarely seen. Their burrows are much deeper than those of the true toads. After heavy rains, they emerge to breed and lay their eggs in temporary pools. This species is so well evolved to live in pine savannahs they can survive the light ground fires that occur in their environment. Fossil evidence of this species dating to the Pleistocene has been found at 10 sites in Florida.

The narrow-mouthed toad is not a true toad but belongs to the narrow-headed frog family. Photo from wild herps.

Narrow-mouthed toads (Gastrophyne carolinensis) are not true toads but instead belong to the narrow-headed frog family (Microhylidae). This species burrows near wetlands and spends much of its time in emergent wetland vegetation. They mostly eat ants. Fossil evidence of this species has been found at Ladds in northwest Georgia.

Woodhouse toads (Anaxyros woodhouseii) no longer occur on the southeastern coastal plain of North America, but their fossil remains have been found at sites in Florida and Alabama. The reason for their regional disappearance is a mystery. Perhaps, unlike other species of toads here, they are not well adapted to human set fires.

Toads secrete poisons that make them unpalatable to mammalian predators. However, toads do make up the majority of the hog-nosed snake’s diet. Toads do have a defense mechanism against the snakes too. They swell their bodies, making them hard for the snake to swallow. Sometimes this defense mechanism works and sometimes it does not.

Giant Sea Snakes of the Georgia Eocene

May 6, 2021

The entire coastal plain of southeastern North America and all of Florida were below sea level until about 32 million years ago. Strong currents carried sediment into shallow coastal waters, and some sediments eventually became kaolin clay, now mined in Wilkinson County, Georgia. The clay preserves fossils of the Eocene Age including shark’s teeth, sawfish and ray bones, and the remains of primitive whales. Miners excavating clay also find vertebrae from an enormous extinct sea snake given the scientific name, Palaeophis virginianus. Scientists compared the vertebrae of Palaeophis with modern species of snakes and estimated this extinct species reached a length of at least 17 feet long.

Artist’s rendition of an extinct giant sea snake (Palaeophis).. Image from the Prehistoric Animals Twitter Page..
Fossil vertebrae of an extinct giant sea snake. Image from an anonymous post on the Fossil Forum.

Palaeophis was not closely related to modern day sea snakes. Scientists don’t know much about it, but they think it was an ambush predator, like a modern day anaconda, that preyed on other animals in shallow coastal waters. There was more than 1 species of Palaeophis sea snakes alive during the Eocene (55 million years BP-33 Million years BP), and they had a worldwide distribution, but today they are extinct and they left no descendants. Palaeophis fossils found in south Georgia are thought to date to ~34 million years ago, close to the end of the Eocene.

Reference:

Calvert, C; A. Mead, and D. Parmley

“Size Estimate of Extinct Aquatic Snakes from the Eocene of Central Georgia”

Georgia Journal of Science 79 (1) Article 22 2021

The Former Abundance of Green Sea Turtles (Chelonia mydas)

April 22, 2021

Our ancestors didn’t appreciate wildlife. For them wild animals were considered either a pest or a resource to be ruthlessly exploited until that particular species was annihilated. I came across an article entitled “Turtling in Florida” written during 1890 and learned how abundant green sea turtles formerly were. According to the author, slaughtering turtles was great sport. So many turtles populated some lagoons that a man could theoretically walk from 1 side to the other by walking on their backs. Turtle stampedes endangered men’s lives. Sea turtles crawling on beaches to lay their eggs could become frightened by men hunting them and their eggs, and hundreds of 800 pound panicking turtles could crush men too slow to get out of their way.

Of course, man is much more dangerous to sea turtles than they are to us. In North America before man invaded the continent, adult sea turtles had few enemies–bears on beaches and tiger sharks in the sea. But man killed too many turtles and gathered too many eggs, and now green sea turtles are endangered. Several methods were formerly used to catch green sea turtles. Some men used nets, though in south Florida, they encountered problems with sharks and sawfish that often destroyed the nets. (Both sawfish and sharks are much more rare now than they were in 1890.) Other turtle-hunters used harpoons in a process called “pegging.” The harpoons were designed to just barely penetrate the shell, so the turtle could be reeled in and kept alive for as long as possible. Some Seminole Indians actually dove to the bottom of the sea, grabbed the turtles, wrestled them to the surface, lassoed them, and pulled them onto the boat. The most common method of hunting sea turtles was to simply sneak up on them while they were laying eggs on the beach, and turn them over. Sea turtles are helpless when on their backs. This method could be hazardous. The turtle-hunters could run into a bear in the dark (turtles lay their eggs at night). The article reports 1 expedition shooting and killing 5 bears on a night of turtle-hunting, and they could have killed more, if the sand flies hadn’t been driving them crazy. There was also the possibility of getting crushed in the aforementioned turtle stampedes.

Green sea turtles inhabit shallow coastal waters where they feed upon sea weed. They nest on tropical beaches.
Green sea turtle range map. They often stray far from where they nest.
Green sea turtles are considered a delicacy due to their vegetarian diet. They were formerly abundant, but overhunting by men has greatly reduced their numbers.
Aborigines can still get away with hunting sea turtles.

Green sea turtles were a popular delicacy over 100 years ago. Adult green sea turtles live on a diet of seaweed, giving their flesh a delicious flavor, according to old time accounts. People enjoyed eating turtle eggs too. No matter how long a turtle egg is cooked, the white part never solidifies. The eggs must have made cakes moist when they were used as an ingredient. The turtle shells were used to manufacture women’s jewelry as well. Now, green sea turtle populations are low and even raising them on farms for food is illegal. Nevertheless, various aboriginal groups around the world still hunt them and collect their eggs.

Reference:

Murphy, J.M.

“Turtling in Florida” from

Tales of Old Florida

Castle Books 1987

Tegu Lizards (Salvator merianae) are Invading Georgia

March 18, 2021

You know who I hate (besides Trumpanzees)?  I hate the hypocritical sadistic do-gooders who hunt Burmese pythons in south Florida.  For generations the ecosystem there has been out of whack because large predators have been reduced or exterminated.  Finally, a new large predator has been introduced (though accidentally), but these stupid jerks are wiping them out too.  Burmese pythons can help control the overpopulation of raccoons and wild hogs in South Florida that destroy eggs of endangered species of turtles.  The snake-killers refuse to acknowledge this benefit, and instead they are doing their best to eliminate another large predator that simply is substituting for the wolves and cougars that humans also try to wipe out.  I hope these assholes fail.  I root for the snake.  In fact I hope 1 day a Burmese python squeezes the life out of a snake-killing hypocrite who is trying to exterminate them. I would celebrate the irony.  I’d love to write the headline “Burmese Python Euthanizes Human.”

The Argentine black and white tegu is another newly colonizing species (which alarmists call invasive) that has wildlife biologists hyperventilating.  This species is native to South America and a popular pet among reptile-lovers.  However, they grow to 3 feet long and reach weights of 15 pounds.  Pet-owners get tired of taking care of such a large lizard, and they release them into the wild.  Tegus established a breeding population in south central Florida where they’ve been munching down on alligator and turtle eggs for 20 years.  Over the past 3 years there have been over 50 sightings of tegus in Georgia, mostly in Toombs and Tatnall Counties.  To determine whether a breeding population exists in south Georgia, scientists conducted a study.  They set out 75 live traps in 3 different locations in those 2 counties for a couple of months.  The scientists caught 2 breeding age females in all that time, indicating to me that they are still uncommon but present.  The authors of the paper wrote they “euthanized” the lizards by shooting them with a .22 rifle.  I hate the word, euthanize, because it makes killing a creature sound sanitized.

Argentine Black And White Giant Tegu, Tupinambis Merianae Or.. Stock Photo, Picture And Royalty Free Image. Image 94513894.

Black and white tegu lizards, native to Argentina and other South American countries, have established a population in Florida and are invading Georgia.  Do-gooder assholes want to wipe them out, but I think for the most part they are harmless.

Native range map for black and white Argentine tegus.

Verified and unverified sightings of tegu lizards in Georgia + trapping sites of the below referenced study.  .

Map of verified and unverified sightings of tegus in Georgia and Florida.  Surprisingly, some of them have been from quite far north in Georgia.  Tegus are partially warm-blooded and can dig burrows, helping them survive in cooler climates.  Map also from the below referenced study.

Most of Georgia is ideal habitat for tegu lizards.  They are partially warm-blooded and can did burrows to escape cold and hot weather.  Females lay about 30 eggs, and the young become full grown and sexually mature in 2 years.  They are also omnivorous, eating insects, other arthropods, small animals, eggs, and fruit.  The stomach contents of 7 tegu lizards trapped in Georgia included blackberry, strawberry, insects, other arthropods, crayfish, wood frogs, and a toad.  This list hardly sounds like an animal that is destabilizing the environment.  Wildlife biologists are concerned the lizards might eat eggs of the endangered gopher tortoise, and they have been found in gopher tortoise burrows, but native raccoons are much more abundant and have hardier appetites.  If gopher tortoises can co-occur with raccoon predation, they can endure the impact of a few lizards.  Unlike Burmese pythons, tegu lizards are much more vulnerable to native predators.  I’m sure bobcats, coyotes, hawks, owls, and snakes can control their numbers.

Reference:

Haro, D.; et. al.

“Evidence for an Established Population of Tegu Lizards (Salvatore merianae) in Southeastern Georgia”

Southeastern Naturalist (19) 4 2020

Deinosuchus rugosus Given a New Scientific Name–D. Schwimmeri

March 11, 2021

My wife took a geology class 40 years ago at Columbus State University, and it was taught by David Schwimmer who now has the honor of having an extinct species of crocodylian named after him.  The paleontologists who named the species after him consider it a new species (or species novum), but it is really not a species new to science.  The first scientist to name the species gave it the scientific name Deinosuchus rugosus.  However, the type specimen used to name the species is not considered diagnostic as it could represent any of the 3 known species of Deinosuchus.  So they used other more complete specimens to describe the anatomy of the species, and they decided to give it the scientific name D. schwimmeri after David Schwimmer who published a book about Deinosuchus during 2002.

Species named after Columbus State professor David Schwimmer | Columbus  Ledger-Enquirer

David Schwimmer of Columbus State University, my wife’s college geology professor.  He wrote a book about Deinosuchus, a giant extinct alligatoroid.  Deinosuchus rugosus has been renamed in his honor as D. schwimmeri.

Feces, Bite Marks Flesh Out Giant Dino-Eating Crocs

Deinosuchus preyed on tyrannosaurs and other dinosaurs.

Fossil evidence suggests there were 3 species of Deinosuchus living in North America during the late Cretaceous from ~80 million years BP-~73 million years BP.  The North American continent was split into 3 land masses by the Western Interior Sea then.  D. schwimmeri is the species that lived on the eastern part of North America, and D. riograndis lived on the western part.  D. hatcheri, a poorly known species, also lived on the western part.  D. riograndis tended to grow larger than D. schwimmeri.  All species of Deinosuchus were 36 foot long 12,000 pound monsters that ate Tyrannosaurus rex for breakfast.  Fossil specimens of Deinosuchus have been found in Georgia, New Jersey, North Carolina, Alabama, Mississippi, Texas, Utah, Nebraska, Wyoming, Montana, and Mexico.  Scientists aren’t sure how Deinosuchus came to live on both sides of the Western Interior Sea.  They likely were saltwater tolerant and perhaps island-hopped from 1 side to the other.  Alternatively, when the Western Interior Sea flooded the Great Plains, the 2 founding populations were separated.

Deinosuchus is considered an alligatoroid or in other words they are thought to have been more closely related to alligators than crocodiles.  They were not ancestral to modern alligators.  Instead they were related to the direct ancestor of modern day alligators.

References:

Gossette, A; and C. Bracho

“A Systematic Review of the Giant Alligatoroids Deinosuchus from the Cretaceous of North America and its Implications for the Relationships at the Root of Crocodylia”

Journal of Vertebrate Paleontology 40 (1) 2020

Schwimmer, David

King of the Crocodylians: The Paleobiology of Deinosuchus

Indiana University Press 2002

 

Pack-Hunting Cuban Boas (Chilabothrus angulifer)

January 8, 2021

Cuban boas work together when they hunt Jamaican fruit bats.  They each take a strategic position near cave entrances to increase the chances they will successfully ambush a bat.  Scientists believe the gauntlet they create requires active coordination.  Otherwise, they would all be laying on top of each other in the best strategic location, and bats could just avoid that area.

Found: Snakes That Hunt in Packs - Atlas Obscura

Cuban boas hunt in packs.  They coordinate their positions near cave entrances and ambush Jamaican fruit bats.  They kill their prey using constriction.

There are 12 species of large boas in the Chilabothrus genus, but each Caribbean Island usually hosts just 1 or at most 2 species.  Each island was colonized by 1 species of boa that drifted there on floating vegetation millions of years ago.  Once that species became established on the island, they precluded other species arriving on floating vegetation from colonizing the island.  Genetic evidence suggests Cuban boas diverged from their closest relative 17-20 million years ago, and since then they have prevented other boa species from establishing a population there.

Cuban boas were part of an unique ecosystem found on Caribbean Islands until it was disrupted by man thousands of years ago.  Cuban boas formerly grew up to 27 feet long, but now individuals larger than 9 feet long are rare.  During the Pleistocene they hunted hutias (large 15 pound rodents), birds, and lizards. They still hunt these species, but larger species of hutias became extinct after man colonized the islands.  Cuban boas may have also hunted the now extinct dwarf ground sloths that roamed the island then.  Cuban boas shared the environment with other predators including Cuban crocodiles, an extinct species of 3 foot tall flightless owl, and large extinct subspecies of barn owls and black hawks.  Since man arrived on Cuba, both boas and crocodiles have evolved to smaller sizes.

The 2 largest predators on Cuba have evolved to a smaller size, since man colonized the island.  Image from the below reference by Rodrigues-Cabrera.

References:

Dinets, Vladimir

“Coordinated Hunting in Cuban Boas”

Animal Behavior and Cognition 4 (1) Feb 2017

Rodrigues-Cabrera, T.; and T. Javier Torres

“An Overview of the Past, Present, and Future of the Cuban Boa, Chilabothrus angulifer, (Squamata: Boidae): A Top Terrestrial Predator on an Oceanic Island”

Reptiles and Amphibians Journal December 2016

A Pre-Historic Sloth-Eating Monster

September 7, 2020

A real monster inhabited the wetlands of South America during the Miocene between 20 million years BP-6 million years BP.  Purussaurus brasiliensis, an extinct 34 foot long caiman, preyed on everything from fish to giant ground sloths.  No complete skeleton of this giant caiman has ever been found, but the size was estimated from several skulls.  It weighed over 10,000 lbs. and was more than a match for any beast living in South America during the time it existed. The few marsupial carnivores that lived then didn’t offer much competition.  It was almost as large as Deinosuchus rugosus, a 39 foot long crocodylian that ate tyrannosaurs during the late Cretaceous.

Purussaurus

Purussaurus was a 36 foot long caiman that lived in South America during the Miocene and preyed on giant ground sloths.

Illustration of purussaurus preying upon a ground sloth.

Recently, scientists examined a fossil arm bone of a giant ground sloth (Pseudoprepothenum) and determined it had 46 tooth marks made by a purussaurus.  At least 6 other species of caiman and crocodiles lived then in South America, but purussaurus was the only species large enough to attack and subdue a giant ground sloth, though this particular specimen was estimated to weigh about 100 lbs. The sloth specimen was found near Iquitos, Peru along with many other fossils of fish, reptiles, and mammals.

Reference:

Pujos, F. and R. Salos-Gismonde

“Predation of the Giant Miocene Caiman Purussaurus on a Mylondontid Ground Sloth in the Wetlands of Proto-Amazonia”

Biology Letters 2020

Another Pleistocene Survivor–The Bird-Voiced Tree Frog (Hyla avivoca)

June 11, 2020

I discovered a new creature in my yard.  Green tree frogs (Hyla cinerea) are abundant here and often sneak into our house, but I was unaware that my yard is also home to the bird-voiced tree frog until I saw the below specimen in my cat’s water dish.  I saw another one a few weeks later.  Most of the time they stay in the tree tops and that is probably why I’d never seen one before, though maybe they had a good few years of reproduction and are on the increase at my locality.  Bird-voiced tree frogs can be green or gray, depending upon the temperature.

Bird-voiced tree frog.

Video of a bird-voiced tree frog call.

Bird-voiced tree frogs have an interesting range distribution.  They likely diverged from their closest living relatives in the Mississippi River Valley and dispersed across Alabama and Georgia.  Their preferred habitat is swampy bottomland forest, and during warm climate cycles this type of habitat is common in the southeast.  The habitat in my yard is a sandhill loblolly pine/sand laurel oak woodland, but McBean Creek bottomland is just about a mile away.  Bird-voiced tree frogs are absent from peninsular Florida.  They may have occurred in peninsular Florida in the past but were extirpated when most of the state was under ocean during marine high stands.

Species Profile: Bird-voiced Treefrog (Hyla avivoca) | SREL ...

Bird-voiced tree frog range map.

I searched the paleobiology database and learned no fossils of this species have ever been found.  A small animal that lives in a forest has a lesser chance of becoming preserved as a fossil.  Leaves turn the soil acid, dissolving bones.  As far as I can determine, no genetic studies of bird-voiced tree frogs have ever been conducted.  It is an understudied species.

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.

Image result for Barbour's map turtle

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

Image result for Barbour's map turtle range

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

Image result for map of Florida during the Last Glacial Maximum

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.

Reference:

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