The Isle of Hope Fossil Site in Chatham County, Georgia

I’ve mentioned the Isle of Hope fossil site numerous times on this blog, but I recently realized I’ve never featured it.  In my opinion it is the 3rd or 4th best Pleistocene fossil site in Georgia, ranking behind Ladds, Kingston Saltpeter Cave, and perhaps Yarbrough Cave.  More vertebrate fossils were discovered here than at any other coastal fossil site in Georgia.  Most other coastal fossil sites were discovered in the 18th or 19th centuries before paleontologists screen-washed sediment for smaller bones, and accordingly the earlier scientists only collected bones of the largest species.  The more recently discovered Clark Quarry near Brunswick may rival the Isle of Hope for best coastal site, but despite the publication of a preliminary report in 2005, the finds at this site have yet to be thoroughly and systematically reviewed in a scientific journal.

The Isle of Hope is an elite neighborhood in Savannah, Georgia.  At high tide, it is separated from the mainland by a small tidal river.  Vertebrate fossils of Pleistocene age have been collected from this river.

The Isle of Hope fossil site was a deposit that occurred on both sides of a small tidal river within the city limits of Savannah.  During high tide this rivulet separates the island from the mainland.  The fossil site was discovered in the early 1980s during construction of a boat pier.  The landowners, and John Heard, an amateur hobbyist, collected the fossils, and later, paleontologists from Georgia Southern also collected specimens from the site.  Most of these specimens are housed at the Georgia Southern Museum.  One side of the site has been “covered in riprap and is no longer accessible for collection.”   However, I suspect this entire tidal river has potential for a hobbyist prospecting for fossils  Tidal action has likely distributed specimens in both directions away from the deposit.  If I lived in Savannah, I’d definitely search for fossils here.

Uranium-series dating and fossil composition suggest the fossils were deposited during a warm interglacial climate phase between ~132,000 BP-~75,000 BP.  Every single species of mollusc and fish found in the fossil deposit still occurs in the region today–evidence water temperatures during this climatic stage were similar to those of today. 

The dwarf surf clam was the most common bivalve species found at the Isle of Hope site.  It is still the most numerically common clam in Georgia tidal inlet channels.

user posted image

Fossil brown-banded wettletraps were found at the Isle of Hope site.

Atlantic sharpnose shark

The Atlantic sharp-nosed shark.  Fossils of this species were the most common fish remains found at the Isle of Hope site.  It’s still the most common shallow water shark found in the region today.

Amazingly, the fishing in coastal Georgia 100,000 years ago would have resulted in the same species typically caught from a modern day pier–sharp-nosed sharks, stingrays, moray eels, sheepshead, black drum, toad fish, and puffers.  Schools of mullet would have been seen swimming by, and little killifish swarmed the shallows.

Eastern mud turtle.  Mud turtles were the most common reptile specimens found at the Isle of Hope site. 

 Photo of Salt Marsh Vole. Photo courtesy of USFWS/Photo by Michael Mitchell.

The meadow vole was the most common small mammal living in coastal Georgia during the Pleistocene.  This species no longer occurs this far south aside from a relic population that lives in a salt marsh in Levy County, Florida.  

There has been an interesting change in the small mammal fauna of coastal Georgia since the Pleistocene.  Then, the most common rodents were the arvicolines, including the meadow vole, southern bog lemming, and Florida muskrat.  The sigmodontine rodents (cotton rat, rice rat, wood rat, and old field mouse) were present but less common.  Today, the 3 arvicoline rodents mentioned above are absent from coastal Georgia while the sigmodontine rodents are common.  The bog lemming no longer occurs this far south.  The meadow vole also doesn’t occur this far south with the exception of a relic population that lives in a salt marsh in Florida.  The Florida muskrat no longer occurs this far north.  Scientists believe the intermingling of warm and cold climate species during the Pleistocene is evidence that climate then was more equible than it is today because formerly winters were warmer and summers were cooler.  I have a different explanation for the co-existence of warm and cold climate species during the Pleistocene.

During some climatic phases, average temperatures were less extreme than they are today, but overall climatic fluctuations were formerly more drastic.  These dramatic climatic fluctuations created more varied habitats that supported a wider array of fauna, especially of small mammals. I think the relatively stable climate of the past 10,000 years is the cause of the more zonal distribution of small mammal species today.  The change in temperature ranges between the Pleistocene and Holocene haven’t been large enough to entirely explain the disappearance of arvicolines from coastal Georgia.  Instead, I think a shift to a more stable climate pattern is a better explanation.  For example, during the Pleistocene a shift to a sudden cold pattern with snowy conditions would have benefited meadow voles over cotton rats because the former are better adapted to living under snow.  A subsequent shift to warm climate would have favored cotton rats, but during Ice Ages the warm climatic phases didn’t last long enough to completely extirpate the cold climate species.  Changes in species composition lagged behind the rapid climatic changes. But over the past 10,000 years, a warm climatic phase that has lasted quite a while, meadow voles did not enjoy the benefits of a sudden shift to cold climate in the south and have mostly disappeared from the region.  Only species adapted to warm climate have been able to continue living in the south.

Perhaps the most mysterious mammal to have lived in Georgia 100,000 years ago was a small cat.  (See https://markgelbart.wordpress.com/2013/05/09/the-mystery-cat-of-pleistocene-georgia/).  A jaw bone of this species was found at this site but not enough skeletal material has been found to determine what species this cat was.  Despite the genus name, Leopardus, it was not closely related to the leopard as some sources have erroneously and carelessly reported (See Roadside Geology of Georgia).  Instead, it was closely related to the margay and ocelot.

White-tailed deer fossils were the most abundant large mammal specimens found here.  Deer may have been more common in Pleistocene Georgia than other species of now extinct megafauna, contrary to other areas such as Florida.  However, specimens of long-nosed peccary, bison, horse, tapir, and mastodon have been found here, showing they did share the environment with deer.  I think if this tidal river were more throughly investigated, fossils of more species would be  discovered, including those of large carnivores which are so far lacking completely from coastal Georgia sites.

Eremotherium laurillardi, the giant ground sloth.  It was common on the Georgia coast during the last interglacial but disappeared from North America some time during the following Ice Age.

Below is a list of all the species found at the Isle of Hope site as reported in the reference cited at the bottom.  I had fun translating the Latin names to English.  Just 1 species of shellfish stymied my attempt to translate them all.

Isle of Hope Species List

Knobbed whelk (Busycon carica)

Brown-banded wettletrap (Epitonium rupicola)

Sea snail (Eupleura caudata)

Lettered olive (Oliva sayana)

Sea snail (Polinices duplicatus)

Eastern auger (Terebra dislocata)

Small white clam (Abra aequalis)

Incongruous ark clam (Anadara brasiliana)

Blood ark clam (Anadara ovalis)

Transverse ark clam (Anadara transversa)

Common jingle shell (Anomia simplex)

? (Divaricella quadrisulcata)

Coquina clam (Donax variabilis)

Dwarf surf clam (Mulinia lateralis)

Ponderous ark clam (Noetia ponderosa)

Atlantic nut clam (Nucula proxima)

3-toothed Cardita (Pleuromeris tridentata)

Nurse shark (Ginglymostoma cirratum)

Sand tiger shark (Carcharias taurus)

Tiger shark (Galeocerdo cuvier)

Bull shark (Carcharhinus leucas)

Dusky shark (Charcharhinus obscurus)

Lemon shark (Negaprion brevirostris)

Sharp-nosed shark (Rhizoprionodon terranovae)

Hammerhead shark (Sphyrna tiburo)

Stingrays (Dasayatidae)

Spotted eagle ray (Aetobatus narinari)

Eagle rays (Myliobatidae)

Gar (Lepisosteus sp.)

Lady fish (Elops saurus)

Moray eels (Muraenidae)

Shad (Alosa sp.)

Herrings (Clupeidae)

Hard-nosed catfish (Arius felis)

Lizard fish (Synodus sp.)

Toadfish (Opsanus sp.)

Ray-finned fish (Batrachoididae)

Killifish (Fundulus sp.)

Sea robins (Prionatus sp.)

Cutlass fish (Trichiurus sp.)

Pinfish (Lagodon rhomboides)

Sheepshead (Archosargus probatocephalus)

Silver Perch (Bairdella cf chrysoura)

Black drum (Pogonias cromis)

Red drum (Scianops ocellata)

Mullets (Mugil sp.)

Barracudas (Sphyraena sp.)

Flounders (Bothidae)

Boxfish (Lactophrys sp.)

Puffer fish (Tetraodontidae)

Porcupine fish (Diodontidae)

Siren (Siren intermedia)

Red Spotted Newt (Notophthalmus viridescens)

Conger Eel (Amphiuma means)

Spotted Salamander (Ambystoma cf maculatum)

Toads (Bufo sp.)

Chorus frog (Pseudacris ornata)

Bullfrog (Rana catesbeiana)

Snapping Turtle (Chelydra serpentina)

Mud Turtles (Kinosternon sp.)

Musk Turtles (Sternotherus)

Soft Shelled Turtle (Apalone ferox)

Box turtle (Terrapene carolina)

Chicken turtle (Deirochelys reticularian)

Slider (Pseudemys cf concinna)

Pond slider (Trachemys scripta)

Gopher tortoise (Gopherus polyphemus)

Extinct Intermediate Tortoise (Hesperotestudo incisa)

Extinct Giant Tortoise (H. crassicutata)

Black Racer (Coluber constrictor)

Bull Snake (Pituophis melanoleucas)

Water snake (Nerodia fasciata)

Queen snake or other Crayfish snake (Regina sp.)

Garter snake (Thanophis sirtalis)

Hog-nosed snake (Heterodon sp.)

cottonmouth water moccasin (Agkistrodon piscivorus)

unidentified rattlesnake (Crotalus sp.)

Unidentified duck (Anas sp.)

Opposum (Didelphis virginiana)

Beautiful armadillo (Dasypus bellus)

Giant ground sloth (Eremotherium laurillardi)

Harlan’s ground sloth (Paramylodon harlani)

Short-tailed shrew (Blarina brevicauda)

Southeastern shrew (Blarina carolinensis)

Eastern mole (Scalopus aquaticus)

Unidentified bear (Ursidae)

Raccoon (Procyon lotor)

River otter (Lutra canadensis)

Margay-like cat (Leopardus sp.)

Bobcat (Lynx rufus)

Southern flying squirrel (Glaucomys volans)

Gray squirrel (Sciurus carolinensis)

Beaver (Castor canadensis)

Rice rat (Orzomys palustris)

Cotton rat (Sigmodon hispidus)

Wood rat (Neotoma floridana)

Old-Field Mouse (Peromyscus polionotus)

Florida muskrat (Neofiber alleni)

Southern bog lemming (Synaptomys australis)

Meadow vole (Microtus pennsylvanicus)

Pine vole (M. pinetorum)

Cottontail rabbit (Sylvilagus floridanus)

Marsh rabbit (S. palustris)

Long-nosed peccary (Mylohyus fossilis)

Bison sp. (Bison sp.)

White-tailed deer (Odocoileus virginianus)

Tapir (Tapirus veroensis)

Horse (Equus sp.)

Mastodon (Mammut americanum)

Reference:

Hulbert, Richard; and Ann Pratt

“New Pleistocene (Rancholabrean) Vertebrate Faunas from Coastal Georgia”

Journal of Vertebrate Paleontology 18 (2) June 1998

 

 

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