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

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.

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.

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.

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.

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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The Pleistocene Ridge and Valley Reptile Corridor

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 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.  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.

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

 

 

 

 

 

Wild Cranberry Bogs–A Relic Ice Age Landscape of the Upper South

The Nature Conservancy is successfully protecting habitat in Shady Grove, Tennessee for the federally threatened bog turtle (Clemmys muhlenbergii), a species small enough to fit in the palm of the hand.  In fact, it’s America’s smallest turtle species.  The bog turtle, as the name would suggest, is dependent on bog habitats, particularly the kind where wild cranberries grow.  Bogs are wetlands that differ from swamps in that they’re poorly drained, whereas swamps may appear stagnant but actually consist of slowly moving water.  Bogs are also more associated with cooler climates.

Range map for the bog turtle.  Part of its present range was under glacial ice during the ice age.  This map isn’t entirely accurate because one of the areas the Nature Conservancy has protected for this species is in Tennessee, which according to this map is outside its range.  During the Ice Age, this species probably had a more continous range and wild cranberry bogs were more common due to differences in climate.

There exists two distinct populations of bog turtles–one in northeastern states, and the other in high elevations of the southern Appalachians.  During the last Ice Age these ranges were likely continuous.  The southern population is threatened by agricultural practices, including the drainage of bogs to increase land for cultivation.  To protect the present day habitat of the bog turtle, The Nature Conservancy, over the past few decades, has purchased small parcels of remaining habitat–the last of the southeast’s wild cranberry bogs, a landscape that was probably more widespread in the upper south during the Ice Age when cool, rainy climate prevailed.  Now, the Conservancy is restoring cranberry bogs by building berms to stop drainage.

The Conservancy leases the land around these bogs to farmers because livestock grazing improves habitat for bog turtles which need more open ground for foraging on insects, berries, and succulent plants.  Modern day livestock play the beneficial ecological role that extinct or extirpated megafauna–mastodons, bison, horses, etc.–used to provide for the turtles.  The turtles need large ungulates to keep excess plant growth in check.

Wood Turtles

The wood turtle (Clemmys insculpta) is a closely related but larger species that also used to range farther south during the Ice Age.

Range map of the wood turtle.  Fossils of wood turtles, a species that prefers cooler climate, have been recovered from Ladds Mountain, in Georgia.

Paradoxically, fossils of the red-bellied turtle, a species that today is limited to Florida, have also been found at Ladds.  Based on carbon dates, at least one scientist believes they occupied the same range during the same period of time, suggesting a more moderate phase of climate occurred during one particular point of time compared with today.  During this climate phase summer must have been cooler but winters must have been warmer.

Source:

Kingsbury, Paul

“Turtle Power: A rare reptile helps restore a Tennessee wetland”

Nature Conservancy  Autumn 2010