Posts Tagged ‘Black Belt Prairie Pleistocene fossils’

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

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Pleistocene Fossils Found in Southwestern Georgia and Southeastern Alabama

August 17, 2015

Geologists refer to the upper coastal plain of Alabama and southwestern Georgia as the “southern hilly Gulf Coastal Plain.”  The terrain alternates between irregular flat plains and gently rolling hills.  Many creeks and rivers erode through sediments of differing ages, exposing fossiliferous deposits that date from the Cretaceous to the Pleistocene.  During the Pleistocene a mosaic of deep forest, open woodlands, savannah, prairie, and wetlands covered this region.  Pollen from composite species (sunflowers, daisies, etc.) and pine increased during arid stadials while warmer wetter interstadials saw an increase in broad-leafed tree abundance.  Most of the plant species that occurred here then are still extant but the extinct Critchfield’s spruce; a temperate species that grew alongside oaks, walnut, and elm; was a component of this primeval wilderness.

Fossil hunters have collected mastodon fossils from Hannahatchee Creek in Stewart County, Georgia; Bogue Chitto Creek in Dallas County, Alabama; and the Warrior River in Alabama. (See:http://www.archeologyink.com/Ice%20Age.htm) Hannahatchee Creek is better known for Cretaceous fossils.  Most of the Cretaceous fossils found here are of marine species but teeth of nodosaurs, hadrosaurs, and tyrannosaurs have been collected from the stream bed.  A mastodon tooth was recovered about 1/2 mile west of Union, Georgia along Hannahatchee Creek, and a leg fragment of a mastodon was picked up upstream near Omaha.  I looked at a satellite image of this creek.  The owners of the land here allow a narrow strip of natural creek bottomland to grow, but most of the area appears to be pine plantation.  This is unfortunate because pine tree farms support very little wildlife.  During the Pleistocene the land bisected by Hannahatchee Creek could have consisted of cypress swamp, bottomland hardwoods, beaver meadows, grassy marshes, and/or canebreaks.  All of these environments would’ve made excellent habitat for semi-aquatic mastodons.

Hannahatchee Creek erodes through strata of different ages from the Cretaceous to the Pleistocene.

Mastodon Tooth

A mastodon tooth was found in Hannahatchee Creek.

Other Pleistocene remains have been recovered from at least a dozen small creeks that flow through the upper coastal plain of Alabama and Mississippi.  They include mammoth, horse, tapir, bison, white-tailed deer, long-nosed peccary, flat-headed peccary, giant beaver (Casteroides sp.), pampathere (a 300 lb armadillo), Jefferson’s ground sloth, Harlan’s ground sloth, gray fox, coyote, Florida spectacled bear (Tremarctos floridanus), giant short-faced bear (Arctodus simus), black bear, margay cat (Leopardus wiedii), and indigo snake.  The margay cat currently ranges throughout tropical forests in Central and South America, but it formerly lived in southeastern North America.  Fossil remains of the margay have been found at 2 sites in Georgia, 12 in Florida, and 3 in Mississippi and Alabama.  The latter 3 are not listed in the Paleobiology database, and I was unaware of these specimens when I wrote a blog post about this species (See: https://markgelbart.wordpress.com/2013/05/09/the-mystery-cat-of-pleistocene-georgia/).

Margay hanging from tree.

Margay fossil remains found in Alabama and Mississippi have not been posted on the paleobiology data base or faunmap.

Horse teeth dating to the Pleistocene are particularly abundant in these small creeks.  This suggests the presence of extensive grasslands in the Black Belt Prairie region that stretches across Mississippi and Alabama.  Disjunct areas of Black Belt Prairie are also found in south central Georgia.  Herds of horses attracted large predators such as dire wolf, saber-tooth, scimitar-tooth, giant lion (Panthera atrox), and jaguar.  There is some scant evidence of dire wolf in this region, but it is undocumented.  Fossil remains of the other 4 large carnivores have been found in adjacent regions, so it’s very likely they occurred on the upper coastal plain.  The first Panthera atrox fossil was found in northern Mississippi, and giant lions are part of Florida’s and South Carolina’s fossil record.  Jaguars fossil remains have been found in Georgia, Florida, and South Carolina. Saber-tooth remains have been excavated from northern Alabama, Florida, Tennessee, and South Carolina.  Scimitar-tooth bones were discovered in Tennessee and Florida.

George Phillips wrote an excellent Masters Thesis about Pleistocene fossils from this region, focusing on the non-mammalian species.  He did mention in his thesis that he would write in the future about ocelot (Leopardus pardalis) and dire wolf (Canis dirus) remains found here.  His thesis was written in 2006, yet I can find nothing on the internet about ocelot and dire wolf remains found from Alabama.  I assume this data is still unpublished.  However, an amateur fossil collector informed me that he collected a dire wolf tooth (along with mammoth, bison, and horse bones) from the Flint River in Georgia.  Dire wolves undoubtedly were a major predator of the upper coastal plain during the late Pleistocene.  As far as I know, no scientist has ever prospected the Flint River for fossils.

George Phillips thoroughly studied fish and turtle remains eroded from streamside fossil deposits.  The fish remains belonged to the same species that swim in Alabama creeks today–gar, bowfin, suckerfish, catfish, freshwater drum, and sunfish.  But some of the turtle remains belonged to species that are extinct or no longer live in the region.  That will be the subject of my next blog entry.

References:

Kurten, Bjorn and John Kaye

“Late Quaternary Carnivora from Black Belt, Mississippi”
Boreas 1982

Phillips, Georgia

“Paleofaunistics of Non-mammalian Vertebrats from the Late Pleistocene of the Mississippi-Alabama Black Belt Prairie”

North Carolina State Masters Thesis 2006

Shwimmer, David

“First Mastodont Remains from the Chattahoochee River Valley in Western Georgia, with implications for the Age of Adjacent Stream Terraces”

Georgia Journal of Science 1991