Posts Tagged ‘hesperotestudo crassicutata’

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

January 13, 2016

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

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

African spurred tortoise at burrow entrance

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

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

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

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

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

Reference:

Meyland and Steyer

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

Zoological Journal of the Linnean Society 2000

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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

The Torreya (Torreya taxifolia) is Missing its Megafaunal Disperser

September 5, 2014

The torreya (Torreya taxifolia), also known as the stinking cedar because its crushed needles give off a strong resin odor, is a relic species thought to have been more widespread during warm climatic phases of the Pleistocene.  It likely diverged from an ancestor that was even more widespread during the Miocene when warm moist forests occurred all across North America and Asia.  T. taxifolia  is an extremely rare species confined to just the east side of the Apalachicola and Flint Rivers, while a closely related sister species (T. californica) is native to California where it is found in several disjunct populations. 

Pleistocene Ice Ages fostered the spread of arid grassland environments that were unsuitable for torreyas.  Under these conditions the torreya retreated to moist refugia on steep ravines of the Apalachicola and Flint Rivers. Connie Barlow, author of the below referenced book, thinks the torreya  formerly expanded its range as far north as the southern Appalachians, following the end of Ice Ages.  They are better adapted to live in an Appalachian cove forest rather than the environments surrounding their current range.  She hypothesizes the torreya’s current rarity is the result of its disperser’s extinction.  She suspects the giant tortoises (Hesperotestudo crassicutata and H. incisa) ate the torreya cones and defecated the seeds intact.  As the climate warmed following the end of Ice Ages, the tortoise’s range expanded and torreya trees spread in correspondence with this range expansion.  She believes the tortoises were the torreya’s main disperser. Squirrels can disperse the seeds but they are more likely to eat and destroy them, and other mammals are all potentially more likely to destroy the seeds with their teeth when they consume the cones. Tortoises don’t have teeth.  Furthermore, torreya cones contain turpene which is toxic to mammals but not to reptiles.  Now that tortoises are extinct, the torreya is stuck within a tiny range where it is probably going to succomb to fungal diseases. 

Barlow’s hypothesis will be difficult to support with concrete evidence–plant macrofossil remains from warm climatic phases of the Pleistocene are rare in this region.

Connie Barlow and her husband with a very rare Torreya tree.  She hypothesizes that its rarity today is due to the extinction of its most probable disperser–the giant tortoise.

Torreya taxifolia range map.png

Torreya taxifolia range map.

Torreya trees grow in natural communities the late naturalist, Charles Wharton, referred to as “torreya ravines.”  These are cool moist micro-environments also known as steepheads, and they only occur on the east side of the rivers.  The dominant trees in a torreya ravine are red maple, southern sugar maple, beech, magnolia, basswood, elm, torreya, and sabal palm.  Most of these species have northern affinities and are more commonly found in Appalachian cove forests.  Other plants found in torreya ravines also represent species of northern affinities such as strawberry bush, hydrangea, and redbud.  Wharton found torreya growing with beech, sourwood, and plum in the Faceville Ravine on the Flint River.

Wharton catalogued Torreya Ravines in his book The Natural Environments of Georgia written in 1978.  A more recent updated version of that book (The Natural Communities of Georgia) written by several authors and published last year does not mention torreya ravines.  I fear this means torreya trees may already be extinct in Georgia.  Wild torreya trees can still be found in Torreya State Park in Florida.

Mature torreya trees grow to 60 feet tall, but today few wild torreyas exceed 6 feet before dying back due to fungal disease.  Torreya trees have been transplanted to the Biltmore Estate in Asheville, North Carolina where they are doing much better than the wild trees.  Torreya trees growing on the Biltmore Estate survived a freeze of -30 F.  This shows they are capable of surviving in more northerly latitudes, and this supports Barlow’s hypothesis.

References:

Barlow, Connie

The Ghosts of Evolution

Basic Books 2000

Wharton, Charles

The Natural Environments of Georgia

Georgia Department of Natural Resources 1978

The Interglacial Invasion of Warm Climate Species into Southeastern North America

January 21, 2012

Humans have been enjoying a relatively stable warm climate phase for roughly 11,000 years now–a period of time known as the Holocene.  We’ve probably been experiencing an interglacial because it’s likely we’re between Ice Ages, although with the extraordinary release of CO2 from industrial activities, there’s no telling when the next Ice Age will occur.  This phase of warm stable climate has allowed agriculture to flourish.  If climate had remained unstable and as cool as it did during the last Ice Age, civilization as we know it may never have come into existence.

The most recent interglacial previous to the present one was the Sangamonian Interglacial which lasted from 132,000 BP-118,000 BP.  Climate during the Sangamonian was even warmer than that of today.  At one point during this interglacial the north polar ice cap completely melted and sea levels were higher than they are now.  Cypress swamps grew as far north as Illinois, alligators swam in rivers flowing through what today is Missouri, and giant tortoises roamed the ridge and valley region of the southern Appalachians.  This wasn’t the warmest era in geological history–it wasn’t even close to as warm as much of the Pliocene, Miocene, Oligocene, etc. ages–but it was unusually warm compared to most of the Pleistocene.  This prolonged warm climate phase allowed many frost sensitive species of vertebrates to colonize much of southeastern North America, at least temporarily.  But because cold phases of climate during the Pleistocene lasted 10 times longer than warm phases, fossils of these tropical and subtropical species are in some cases extremely rare.  There are probably more species than the following pictorial cavalcade illustrates, but these are the ones confirmed by science.

Eremotherium laurillardi, the largest ground sloth to ever live in North America, grew to 18 feet long and weighed up to 3 tons.  Fossils of this species are quite common along Georgia’s coastal fossil sites which mostly date to the Sangamonian and early Wisconsinian.  Cold climate eventually drove them from what is now Georgia, but they persisted in Florida until maybe 30,000 BP when the beginning of the LGM became too cold for them even there.  They did continue to live in South America until 10,000 BP when hunting Indians likely drove them to extinction.  If it wasn’t for man, they may have recolonized the gulf coast of today.  2 species of ground sloths (Jefferson’s and Harlan’s) were able to survive in North America during the Ice Age, but Eremotherium must have been incapable of tolerating frosts.

Evidence that the South American marsh deer (Blastoceras dichotomous) once lived in the southeast comes from 1 mandible found at Saber-tooth Cave in Florida.  It was given the scientific name, Blastoceras extraneous, but was likely the same species populating the present day South American pampas.  Dr. Richard Hulbert expressed doubt in his book, The Fossil Vertebrates of Florida, that this mandible was correctly identified, but that was before he himself indentified the presence of collared peccaries in the Florida Pleistocene–a big surprise.

Collared peccaries were only identified from the Florida Pleistocene within the last few years.  Apparently, they colonized the south during the Sangamonian and probably other interglacials.  2 other species of peccaries–the flat-headed and the long-nosed–did commonly occur in the south during cold stages as well.

1 ocelot specimen from the Florida Pleistocene proves this cat lived in the south.  It seems that this cat should be able to survive in Florida today.  I suspect Indians coveting its spotted coat led to its demise there.

Fossil evidence of a small species of cat resembling the modern day margay comes from Florida and 2 widely separated sites in Georgia–Ladds and the Isle of Hope site.  Scientists are uncertain of the identification–it’s either a margay,  jaguarundi, or a distinct extinct species.  Despite the scientific genus name, Leopardus, it’s not at all closely related to a leopard.  Was it climate or paleo-Indian desire for spotted coats that restricted this species to isolated jungles?

Giant tortoise fossils dating to the Pleistocene were found at Ladds, the northernmost locality, though during the Pliocene, which was mostly warmer than the Pleistocene, they lived as far north as Kansas.  In contradiction to what most scientists think, I suspect giant tortoises were capable of surviving light frosts.  See my reasoning in a blog entry from my April 2011 archives.

In the Sangamonian of Georgia I suspect alligators may have ranged into the Etowah River.  If giant tortoises lived in the area, alligators surely must have been able to live there too.

Many species of South American and Central American birds also extended their range north in Sangamonian times.

The Extinct Pleistocene Giant Tortoise (Hesperotestudo crassicutata) Must Have Been Able To Survive Light Frosts

April 15, 2011

Illustration of the extinct giant tortoise that lived in the southern parts of North America.  It grew as large as the Galapagos Island tortoises but was more closely related to the much smaller extant gopher tortoise.

Scientists often use the presence of giant tortoise fossils as a proxy for past temperatures.  They conclude that because giant tortoises can not survive freezing temperatures than they must have lived during a time when the region was completely frost free.

Hesperotestudo crassicutata scute

Photo of part of a tortoise shell or scute from a specimen found in Texas.

Three species of closely related land tortoises lived in southeastern North America: a giant species (Hesperotestudo crassicutata) that grew as big as modern day Galapagos Island tortoises, an intermediate-sized species (Hesperotestudo incisa), and the gopher tortoise (Gopherus polyphemus) which is still extant.  It has occurred to me that the two larger species must have been able to survive light frosts, otherwise they would have become extinct when Ice Ages began.  Here are 5 reasons why I have come to this conclusion and disagree with the scientific consensus that the presence of tortoise fossils indicates warmer winters in this region than those of today.

1. The giant Pleistocene tortoise existed for at least 2 million years.  Within this vast time span, there must have been climatic phases, or at least events of crazy weather, that led to frosts in the deep south.  Today, frosts occur as far south as

Look at how much average temperatures fluctuated before the Holocene (~11,000 BP) when it’s assumed once a decade frosts began occurring in south Florida.  Notice also how much lower average temperatures were previous to the Holocene.  It doesn’t make sense the frosts in the deep south just began occuring 11,000 years ago.  They must have occurred before then.

south Florida at least once a decade.  It doesn’t make sense that these once a decade frosts just began to occur ~11,000 years ago and were absent for the previous 2 million years.  It just seems improbable that frosts began to occur in the deep south during the Holocene, a time of relative climatic stability, but didn’t occur during the Ice Ages which were times of dramatic climatic fluctuations (as the above chart shows) and generally of cooler climates.  If it’s true that giant tortoises couldn’t survive in an environment of light frosts, than that means they were extirpated in the southeast every time there was a frost.  They could only recolonize the south from enclaves in central America or what’s now Mexico, but that would mean a geographical corridor in the deep south must have remained frost free for thousands of years at a time–an unlikely climatic scenario, even during warm interglacials.

2. Scientists believe giant tortoises couldn’t escape the cold because they didn’t dig burrows.  This is a shaky assumption.  The only surviving species of giant tortoise lives on islands near the equator where there are no frosts.  As I discussed with my first point, Hesperotestudo did evolve in a region that must have had occasional light frosts, and therefore to survive, it must have evolved adapatations to escape the cold.  Moreover, Hesperotestudo is not the same species as extant giant tortoises, and we have no knowledge of its behavior patterns.  It’s closest living relative, the gopher tortoise, has a deeply innate instinct to dig burrows, and I see no reason for the assumption that giant tortoises didn’t also dig burrows.  Sea turtles dig deep pits to lay their eggs, proving that size is no obstacle to digging deep holes.

Gopher tortoises dig extensive burrow systems. The giant Pleistocene tortoise was closely related to the gopher tortoise.  There is no reason for the assumption that they did not also dig burrows which would have helped them survive frosts.

3. There is no evidence of tropical plants or pollen in the Pleistocene fossil record of the deep south.  If winters were warmer than those of today, and frost free, there should be fossils of tropical species of plants.  Instead, for example, a study of fossil plants from a site in the Aucilla River in north Florida, dating to the Pleistocene, found almost the exact same species that exist in the region today.  No tropical species were found.  Only 3 species outside their present day region were discovered here–osage orange, wild squash, and hazlenut. All three are temperate species, and the latter prefers cooler temperatures than exist today here.

4. Fossils of extant mammal species tend to be on average of individuals larger than those of the same species found in the region today.  According to Bergmann’s Rule, this indicates cooler climates and precludes warmer winters.

5. The prolonged freeze of 2009/2010 in south Florida caused a high mortality rate of the invasive Burmese python but did not cause their complete extirpation.  It seems reasonable to suppose that eventually, large reptiles that are maladapted to occasional frosts, would through selective pressure evolve to have an adapatation that enables them to seek thermal refuges.  And in fact, there are 2 clades of Burmese pythons with differing behavior patterns in their responses to frosts: the majority of the ones imported for the pet trade come from southeast Asia, and they’re naive to frost; but another population of this species occurs in temperate regions, and they’ve learned to seek refuge and hibernate during colder times of the year.

Like the northern population of Burmese pythons, and the American alligator, the giant Pleistocene tortoise was likely an animal of the subtropics that extended its range into southern temperate regions during warmer climatic stages.  And like pythons and alligators, selective pressures chose those individuals that took action to escape frost.  Alligators know to escape frost by moving into deep water, while caimans and crocodiles and southern Burmese pythons continue basking in subfreezing temperatures which leads to their deaths.  Like the alligator, Pleistocene giant tortoises must have survived frosts by moving to thermal enclaves such as burrows they dug themselves, the dens of other species, caves, hot springs, or under upturned tree roots.  How they survived frost is a subject for conjecture, but I have no doubt that somehow they must have.

Tamias aristus, the Extinct Kicked-up Version of the Eastern Chipmunk

January 20, 2011

Ladds Mountain, located in northwestern Georgia, is perhaps one of the best Pleistocene fossil sites in the state and yields the most mammalian species of any, though not many are of the famous large species.  Many caves and fissures pockmarked the mountain.  During their existence, these caves afforded dens for the animal life of the time, but eventually they collapsed and eroded.  Fortunately for fascinated scientists, the calcareous flowstone mixed with red clay to preserve the fossils.

I took this photo of Ladds Mountain, Bartow County, Georgia.  A fence prevents honest people like me from trespassing to hunt for fossils.

The numerous fossils of small species found here provides intriguing clues about the paleoenvironmental conditions at the time they lived.

One of the interesting small species was the giant or noblest chipmunk (Tamis aristus).  Its anatomical characteristics were exactly the same as those of the living eastern chipmunk (Tamias straiatus) with the exception of a notable size difference–the extinct species was 10%-30% larger.

Skull comparison between the two species of chipmunks from a paper written by Clayton Ray.  Tamias aristus was larger but otherwise they’re similar.  I also notice a suture on top of the skull of the larger species that doesn’t appear on the specimen of the smaller species.

Photo of an eastern chipmunk from google images.  I chose this one because it shows the species in its favored habitat–in a rocky woodlot.  Chipmunks store food in cheek pouches and carry it to tunnels under boulders and tree roots where they hoard the food.  They become dormant during bad weather.  I believe this is why they survived the Ice Age while its larger cousin did not.  During the last interglacial it co-existed with its larger cousin.

Clayton Ray first studied the fossil remains of the giant chipmunk in the 1960’s.  He tentatively decided that it was a distinct extinct species, though he believed it may have merely been a larger subspecies of the still extant eastern chipmunk.  Today, the eastern chipmunk reaches its southernmost range limit in central Georgia.  They live around Atlanta and Athens but are absent in Augusta.  There are more rocky boulders and crevices in the piedmont than there are in the coastal plain. Chipmunks like to tunnel and den in and around big rocks.  The coastal plain is also a tad warmer, allowing chipmunk-eating snakes to be active for a longer time period of the year.  I consider these two factors to be the reasons chipmunk ranges are limited in the south to the piedmont and mountain regions.

Tamias aristus is not common in the fossil record, though that doesn’t necessarily mean it wasn’t successful and abundant for a time.  Fossil specimens have only been recovered from one site other than Ladds–Arredondo IIA, located in north central Florida.  Fossils from Arredondo IIA are thought to be Sangamonian in age.  The Sangamonian was a warm interglacial period lasting from ~132,000-~118,000 years BP.  No good radiometric dates from any of the fossils found at Ladds have ever been recorded, indicating the fossils were too old for carbon dating (carbon dating isn’t possible for fossils older than 50,000 years).  As far as I know uranium series dating and pottasium-argon dating have never been attempted or aren’t possible here.  However, fossil specimens of the extinct giant tortoise (Hesperotestudo crassicutata) and the Florida red-bellied turtle (which today only occurs in Florida) were recovered from Ladds–evidence that the fossils accumulated here during a period of time when the climate was much warmer than that of today.  This also fits Ladds in with a Sangamonian interglacial age along with Arredondo IIA.

Conversely, a few species found at the site indicate cooler climate as well, but it’s not a convincing list–none are definitively dependent on a cooler climate–and it’s unclear whether fossils of different ages are mixed here.  The late Dr. Alan Holman, North America’s foremost authority on Pleistocene reptiles and amphibians, studied the cold blooded vertebrates found at Ladds, and he determined the all lived here during the same phase of climate.  In my opinion  based on the preponderance of temperate and warm weather species, the Ladds fauna is probably from a full blown interglacial period.

Dr. Alroy tackled the problem of determining the age of fossil sites hampered by the lack of quality radiometric dating.  Using the known ages of species appearances and disappearances in the fossil record as a kind of index, he estimates the ages of sites.  He calls this “appearance event ordination” or AEO.  This method is necessarily a very rough and inexact estimate.  Nevertheless, he estimated the age of the fossils found at Ladds to be about 300,000 years old.  One of the species he uses as an index for Ladds is the Vero tapir.  He placed the Vero tapir as existing until 300,000 years BP, but I believe he made a mistake.  Bjorn Kurten considered the Vero tapir to be the common southeastern species of tapir until the megafauna extinction of ~12,500 years BP.  Moving the disappearance date of the Vero tapir changes the estimated date of Ladds fossils.  I have no way of knowing for sure, of course, but because the species of fossils here are so similar to those at Arredondo IIA, I suspect it’s also Sangamonian in age.  I’m more certain that the animals here did live during an interglacial of some kind, if not the Sangamonian, than the Yarmouthian (~200,000 BP) or the Aftonian (~300,000).

Tamias aristus  apparently co-existed with Tamias striatus because the fossils of both are found at Ladds.  They obviously share a common ancestry, probably evolving from the same species.  I hypothesize that their ancestor evolved along two lines:  the larger species grew bigger because it foraged year round, while the smaller species became dormant during bad weather.   Both species did well in the rich oak and chestnut forests of the interglacial age and perhaps well into the early Wisconsinian Age when the climate was still mild.  But as the climate became drier and cooler, grassland replaced forests.  The remaining forested areas provided limited habitat, and the smaller chipmunk adapted better.  I believe the smaller chipmunk had a survival advantage because it became dormant during the bad weather of the Ice Age.  The larger chipmunk could function year round–an advantage in a warm climate.  But it lost that advantage during the Ice Age and instead became victim more frequently to hungry predators in winter, while its smaller cousin stayed hidden and safe during times of the year when food became scarce for carnivores.

Here’s the list of mammalian species found at Ladds and Arredondo IIA.  Notice the striking similarities.  Note: there were other species living near these sites that never perchance left fossil evidence at either one. 

* denotes species found at both sites.  X denotes extinct species.

Mammalian species found at Ladds

*opposum

masked shrew

smoky shrew

*short tailed shrew

*eastern mole

little brown bat (cf)

gray myotis

eastern pipistrelle

big brown bat

*X Jefferson’s ground sloth (probably)–Ray refers to it as species indetermined

*X beautiful armadillo

* New England cottontail–I think it a rather dubious feat to be able to determine subspecies based on a few fossil bones.  This may have been a large subspecies of interglacial rabbit that grew this size due to high quality foraging in a rich forest

*X Noblest chipmunk

Eastern chipmunk

woodchuck

beaver

* rice rat

deer mouse

white footed mouse

X unnamed extinct species of mouse in the Peromyscus genus

* cotton rat

*woodrat

*Florida muskrat

muskrat

southern bog lemming

meadow jumping mouse

*X dire wolf (probably)–Based on one tooth, Clayton Ray considered it to compare favorably to the gray wolf.  Dr. Nowak, the foremost authority on Pleistocene canids, later looked at this tooth, and wrote that it did fall within the size range of dire wolf.  Because Ladds probably dates to the Sangamonian interglacial, it must belong to a dire wolf because gray wolves didn’t colonize North America yet.

*gray fox

black bear

X Florida spectacled bear

raccoon

fisher

* long tailed weasel (cf)

spotted skunk

striped skunk

hog-nosed skunk

river otter

* jaguar

cougar

* bobcat

X river cat–Scientists are unsure whether this was a distinct extinct species, a margay, or a jaguarundi. 

*X Vero tapir

horse

*X long nosed peccary

*X flat-headed peccary

* white tailed deer

X at least one species of unidentified ungulate, the teeth were in too bad a condition to determine the species

5 species of birds left fossils here too, including turkey, black duck, ruffed grouse, passenger pigeon, and a perching song bird

Dr. Holman recoded 22 species of reptiles and amphibians

Mammalian species found at Arredondo IIA

*Opposum

*X Jefferson’s ground sloth

*X beautiful armadillo

* short-tailed shrew

* eastern mole

least shrew

northern yellow bat

southeastern myotis

X Pleistocene vampire bat

eastern pocket gopher

southeastern pocket gopher

southern flying squirrel

*X noblest chipmunk

gray squirrel

*Florida muskrat

Florida mouse

cotton mouse

old field mouse

woodland vole

meadow vole

X Florida bog lemming

harvest mouse

* cotton rat

* rice rat

* wood rat

golden mouse

* rabbit in the cottontail genus

* long tailed weasel

*dire wolf

*gray fox

* jaguar

* bobcat

*X Vero tapir

*X long-nosed peccary

*X flat-headed peccary

* white tailed deer

X upland bison–Bison antiquus

X long-necked llama

X big headed llama

The paleodatabase lists 15 amphibians but just one reptile as being recovered here.  I think this is incomplete.  I believe more reptiles than that were found here but just haven’t been listed on that source.  42 species of birds, including 3 extinct kinds were found here, but again, they’re not listed on the paleodatabase.

The predominant environment at both sites during the Sangamonian interglacial was probably a rich oak and chestnut hardwood forest interspersed with small prairies and dotted with swamps and marshes.

References

Holman, Alan

“The Herpetofauna of Ladds Quarry”

National Geographic Research 1 (3) 1985

Ray, Clayton

“Pleistocene Mammals from Ladds, Bartow County, Georgia

Bulletin of the Georgia Academy of Science 25 (3) 1968

The paleodatabase.

(I’m still trying to get my hands on a copy of Clayton Ray’s 1965 paper devoted exclusively to the extinct chipmunk.  If I do, I’ll write another entry with any new details I learn.)

 

Top Ten Pleistocene Animals I would bring back to the Present, if I could

December 23, 2010

(Warning: I’m jumping on my soapbox for this blog entry.)

Merry Christmas?  I say bah humbug!  Christmas is an ancient pagan holiday celebrating the winter solstice–the shortest day of the year–with a festival of artificial lights.  The Romans knew how to party, and they turned this festival into a drunken orgy known as Saturnalia.  They gave toys to their kids to distract them, so the children wouldn’t be aware that their parents were engaged in a little joyful wife and servant swapping.  The Catholic Church gained political power in the 4th century, but the hierarchy was unable to stop the alcoholic sex-crazed fun.  Instead, they incorporated the holiday and falsely claimed it to be the birthday of Jesus, the invisible Jewish rabbi who the psychotic founders of Christianity believed was the son of God, after God supposedly deposited his sperm into Mary’s vagina without breaking her hymen.

Pious Christians tried to break the real spirit of what the winter solstice should be about, but they haven’t ruined it nearly as much as the oppressive rulers of today’s American society have.  Big corporations and monstrous merchants have transmogrified this glorified sex orgy into a psychological compulsion for working class people to waste money on a bunch of junk they don’t need, so that wealth is transferred from the poor to greedy merchants.  Clueless economists make the ridiculous claim that this is good for the economy.  In reality it’s only beneficial for credit card-owning banks who for the rest of the year use this expensive spending orgy to drain working class people’s money, like vampires sucking the blood of sheep.

I’m not interested in material objects, but I do have a Christmas wish that a magic Santa could transport live specimens of extinct Pleistocene animals to the present so scientists could study the beasts, and zoos could display them.  Here’s my top ten wish list:

Photo of a replica skeleton of Ermeotherium that I took at the Skidaway Island museum.

1. Eremotherium laurillardi–a giant ground sloth.  There’s nothing like this beast living today.  Diminutive South American tree sloths are the closest living relative, but c’mon, there’s just no comparison.  This massive beast lived on Georgia’s coastal plain until about 30,000 years ago which is the time the last glacial maximum began.  The climate became too cold for them in North America, but they persisted in South America until about 11,000 years ago.

2. Smilodon fatalis–the saber-toothed cat.  There’s nothing like this alive today either.  Maybe we could lead a horse or cow into its cage and solve the mystery, once and for all, how it killed its prey.

3. Glyptotherium floridanum–Glyptodont.  A mammal built like a turtle and the size and shape of a Volkswagon.  Who wouldn’t want to see this in person?

4. Mammut americanum–Mastodon.  I’d pick mastodon over mammoth.  Mammoths are closely related to extant living Asiatic elephants, but mastodons were much more primitive and were related to an ancient order close to the evolutionary foundation of elephant-like animals.

5. Megalonyx jeffersonii–Jefferson’s ground sloth  This was a smaller ground sloth about the size of an ox.  For ecological reasons I believe this was the most common kind of ground sloth found in Georgia during most of the Pleistocene.  It preferred forested environments and was better adapted to colder temperatures, living as far north as Canada.

6.  Glossotherium harlani–Harlan’s ground sloth. Co-existed with Jefferson’s ground sloth, but apparently preferred open meadows as opposed to the forested conditions frequented by the other.

7. Mammuthus colombi–Columbian mammoth.  An elephant adapted for living in a temperate region.  Definitely unique enough to make my Christmas wish list.

8. Dinobastis serum–Scimitar-toothed cat.  Not as famous as Smilodon but equally as fascinating.  Got to give it the edge over other mammals left off the top ten list such as the Pleistocene vampire bats, extinct javelinas, and extinct llamas.  Though interesting, those other species do have similar living relatives, but there are no species of fanged cats left on the planet.

9. Terratornis sp.–The terratorn.  It’s a condor with a 14 foot wingspan.

10. Hesperotestudo crassicutata–This giant tortoise lived on Georgia’s coastal plain during warm interglacials and interstadials.  It grew as big as modern day Galapagos Island tortoises, but was closely related to extant gopher tortoises.

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The nature lover in me did get a real gift this year in time for Christmas.  The state of Georgia is going to purchase 15 square miles of Oaky Woods in Houston County.  Currently, it’s being managed as a wildlife management area, but real estate developers were threatening to destroy it.  Oaky Woods is a unique wilderness.  It’s the last stand of the black bear in the piedmont region of Georgia, and it’s home to 4 state record trees.  The landscape consists of mature stands of mixed pine and oak as well as rare remnants of blackbelt prairie, a probable relic habitat dating back to the Pleistocene.  Moreover, there is some good fossil-hunting ground there.  Eocene marine fossils are commonly found on this piece of land.

See www.saveoakywoods.com

Augusta radio talk show host, Austin Rhodes, suggested I go live in a tree when I brought this subject up on the Augusta Chronicle message board.  What a jerk!  The site is now protected, however, no thanks to shmucks like him.

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My next entry will be about ice berg keel scours off the coast of South Carolina. 

Cool.