Exploring Georgia's Natural History
  • Natural History & Geology
    • Podcast; The Tivola Whale
    • Coastal Plain Correlation Chart
    • GA Paleo Research by Paul F. Huddlestun PhD >
      • Late Eocene & Older... Coastal Plain Stratigraphy
      • Washington County Core Logs By Paul Huddlestun
      • Coastal Plain Core Logs by Paul F. Huddlestun
    • Presentation; Oaky Woods Stratigraphy
    • Physiographic Map of Georgia
    • Fossils of Oaky Woods
    • Collections & Stewardship of Georgia’s Fossils
    • I, Periarchus (A Fossil's Tale)
    • Georgia's Amateurs >
      • Amateur; Jared Dyche, On The Way To A Degree
      • Cam Muskelly, Duluth, GA
      • Kyle Keller, Valdosta, GA >
        • Kyle Keller Returns, Still Rocking!
      • Hank Josey, Dublin
      • Bill Christy; Kamin Performance Minerals Fossils
    • Public Fossil Locations >
      • South Houston County Fossils
      • Updated; Islands of the Savannah River
    • Georgia Fossils in the Smithsonian
  • Education Material
    • My Field Kit; What You Need In The Field
    • Meet Crassostrea gigantissima, Georgia's Historic Giant Oyster
    • Georgiacetus Presentation; A Whale for Georgia
    • The Natural History & Fossils Record of Houston County, GA
    • Evolution in Georgia's Fossil Record
    • Georgia's State Fossil; Shark Teeth
    • Georgia's Paleontology For Georgia's Classrooms
    • SW GA RESA 2018 Talk
    • Library & School Presentations
    • An Introduction To Fossils; Presentation
    • Georgia's Fossils Presentation; 500 million years
    • Georgia College Natural History Museum
  • Meteorites
    • Did I Find A Meteorite?
    • Georgia's Lost Meteorite
    • Georgia's Witnessed Meteorite Falls
    • The Sardis Iron, Georgia's Largest Meteorite
  • 1: Georgia's Oldest Fossils; Archaeocyathids, At 513 Million Years Old
  • 2: Trilobites; 500 Million Years Ago
    • 2A; Murray County Stromatolites
    • 2B; A Trilobite Nest in Georgia
  • 3: Geologic Time
  • 4: Our Oldest Vertebrate?
  • 5: Georgia Before the Dinosaurs
    • 5A; Georgia’s Pennsylvanian Plant Fossils
    • 5B: Carpentertypus durhami, Georgia’s Giant Insect, 315 Million Years Ago
  • 6: 200 Million Years Ago
    • 6A: Birth of the Atlantic Ocean
  • 7: Cretaceous Georgia, Dinosaurs & more
    • 7A: Georgias Pterosaur
    • 7C: Coelecanths
    • 7B: So Many Sharks
    • 7D: Xiphactinus vetus
    • 7E: Side-necked turtles
    • 7F: Marine Reptiles
    • 7G: Dinosaurs in Georgia
    • 7I; The Blufftown Formation
    • 7L: Bill Montante's Mega "Gator" Tooth Discovery
    • 7K: The Pio Nono Formation
    • 7J: The Eutaw Formation
    • 7H: Deinosuchus schwimmeri in Recognition of Dr. David Schwimmer
  • 8: Suwannee Current, Gulf Trough, & Bridgeboro Limestone
  • 9: The Clayton Formation Report; By Hank Josey
    • 9A: The Georgia Turtle
  • 10: The Eocene; Georgia's Oldest Mammals
    • 10A: The Origins of Whales
  • 11: A Whale For Georgia
  • 12: Basilosaurids; The First Modern Whales
    • 12A: Basilosaurus cetoides
    • 12B: Basilotritus
    • 12C: Cynthiacetus (Revised)
    • 12D: Chrysocetus
    • 12E: The Redmond Mandible of Albany Ga
    • 12F; Houston County, GA Basilosaurus to the Smithsonian
  • 13: Ziggy and The Museum of Arts & Sciences, Macon, GA
  • 14: Late Eocene
    • 14A: Eocene Fossils & Stratigraphy
    • 14B; Fossils, Impacts, & Tektites Dating the Clinchfield Formation
    • 14C: The Tivola Limestone
    • 14D: Twiggs Clay Vertebrates
    • 14F; Sandersville Limestone, By Hank Josey
    • 14E: Ocmulgee Formation Vertebrates
    • 14I: Dating Late Eocene Sediments
    • 14J: Georgia's Tektites; Georgiaites
    • 14K; Shell Bluff; Georgia's Most Historic Paleontology Site
    • 14L; Taylors Bluff, Paleo Paddling the Ocmulgee River
    • 14M; Eocene Terrestrial Mammals From Gordon, GA
    • 14N: Fossil Ridge, A Stratigraphic Study in Oaky Woods Wildlife Management Area
    • 14O; Georgia's First Entelodont
    • 14P: Historic Rich Hill
    • 14Q; Bibb County's Christy Hill, Clinchfield Formation Hilltop
  • 15: Early Oligocene
    • 15A: The Marianna Limestone
    • 15B; The Glendon Limestone
    • 15C: Undiffereniated Oligocene Residuum
    • 15D; Brissus bridgeboroensis; A New Echinoid Species From Georgia’s Bridgeboro Limestone
    • 15E: The Curious Steinkern Sea Biscuits of Red Dog Farm Road
    • 15F: Early Oligocene Gordian Knot
  • 16: Bonaire GA Entelodont
  • 17: The Whale Eating Shark
  • 18: Miocene Epoch; 23.3 to 5.3 Million Years Ago
    • 18A; Miocene Terrestrial Vertebrates
    • 18B; Paul Fell, Rockhouse Cave
    • 18C: The Marks Head Formation
    • 18D: Miocene Terrestrial Vertebrates of the Marks Head Formation
    • 18E: The Statenville Formation
    • 18F: South Georgia’s Dugong Metaxytherium calvertense
  • 19: Pliocene Epoch; 5.3 to 2.5 Million years Ago
    • 19A; Two Small Primitive Horses from Taylor County
  • 20: The Ice Ages; Pleistocene & Holocene Epochs
    • 20A; Clark Quarry's Mammoths & Bison
    • 20B: Pleistocene Vertebrate List
    • 20C: Georgia’s Eolian Dunes
    • 20D: Georgia’s Carolina Bays
    • 20E: Late Pleistocene Significant Events
    • 20F: Southeastern Thermal Enclave
    • 20G; Diamond Back Terrapins
    • 20H; A Kaolin Mine Beaver Dam
    • 20I; Pleistocene Vertebrate Fossils On Georgia’s Piedmont
    • 20J; Watkins Quarry Pleistocene Vertebrates, Glynn County, GA
  • *NEW* 20K: Pleistocene Vertebrates from Coastal Georgia
  • 21: Humans in Georgia
  • 22: Geology of the Coastal Plain, 1911
    • 22A: 1911 Cretaceous Fossil Locations
    • 22B: 1911 Eocene Fossil Locations
  • 23: Coastal GA Locations (1957)
  • 24: Needed; The Georgia Geologic Survey
  • Building This Site
    • Origins Of This Site
    • Contributing Artists
    • Black & White Sketches

​14A: The Late Eocene Coastal Plain

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Researchers have been studying Georgia’s extremely complex Coastal Plain sediments for more than a century, dozens of papers have been published on the subject and each paper answers many mysteries but reveals even more.

I have tried to be as precise as possible, but the truth is that without a solid understanding sea level changes and the processes of deposition and erosion it is difficult to grasp the Coastal Plain.

The stratigraphy of Houston County is well understood and this is somewhat in the center of Georgia and the northern Coastal Plain; go 20 miles in any direction and everything changes.

Take Tivola Limestone in Houston County; it averages about forty feet thick and is almost entirely marine in character; formed by the fossils of tiny marine organism.  Underneath it (underlying) is the Clinchfield Formation going down for perhaps thirty feet is a terrestrial-source formation of mostly quartz sand deposited by rivers. On top of the Tivola Limestone (overlying) is the Twiggs Clay at nearly one hundred feet thick, depending on your location, and it is also a terrestrial-sourced formation made up of inland clays and silt deposited by the same rivers.

Get in your car and drive twenty miles east and you’ll find both the Twiggs Clay and the Clinchfield Formation, but the Tivola becomes sporadic.

Picture
Source; Upper Eocene Stratigraphy of Central & Eastern Georgia. Paul F. Huddlestun & John H. Hetrick, Bulletin 95, Georgia Geologic Survey, 1986
Picture
Source; Upper Eocene Stratigraphy of Central and Eastern Georgia. Paul F. Huddlestun and John H. Hetrick. Bulletin 95. Georgia Geologic Survey. 1986
Returning for a moment to sea level change, deposition and erosion; bear in mind that Georgia is a land of several large flowing rivers. These rivers are ancient and were present during all this sea level change. 

Advancing coastlines reached the Fall Line and further north repeatedly, then fell again all the way (at times) to the continental shelf. Our rivers endured through all of this, but their courses and estuaries shifted with sea levels. 

The characteristics of the rivers also changed; sometimes they were thick with sand, sometimes they were thick with clay and silt; sometimes then ran clear. Even within the beds of any given formation repeated change in river conditions is often evident. Rivers, of course, carry terrestrial sediments; sediments whose origins are inland. In the case of our rivers and the Late Eocene formations we’re discussing, these sediments are terrestrial sediments deposited in a marine, coastal environment where the rivers become estuaries emptying into the sea.

The separate beds of sediments within any given formation might reflect local, regional or global changes in conditions while they were being deposited. These changes might be minimal, or major. Since many of the Middle Georgia marine deposits are influenced by local rivers flowing into the sea the sediments could either be terrestrial or marine. A bed might reflect the passing of a storm or a drought. It could represent a red tide episode. A landslide one hundred miles inland might be recorded in the coastal sediments of an estuary.

If an impact event or volcanic eruption occurs regionally or globally it can often be dated by finding which bed contains debris from associated tsunamis, impact ejecta, or ash. The formations are like chapters in a history book, the beds are like pages in the chapters.

This is stratigraphy, the geologic study of layers. In the case of the Coastal Plain this study is almost always about sedimentary rock, of deposition and erosion. Earth not only writes its history in the rock, it also erases portions of that history.

The thickness of a bed doesn’t necessarily have any bearing on how long it took to deposit it; rather it reflects conditions, how fast deposition occurred and how much material was present.

 
Clinchfield Formation
The Clinchfield Formation breaks down into four members (or variants); 
The Riggins Mill Member
The Treadwell Member
The Albion Member 
The Utley Member

There is no room to cover all three here and many of the reports for Clinchfield Formation fossils predate their separation in the literature. Since there is no way to know which member produced these older reported finds we’ll treat the three members together here.

The Clinchfield Formation represents Georgia’s most widespread, vertebrate fossil bearing sediments from the Eocene Epoch. It ranges from South Carolina to Roberta, Georgia. 

The Roberta, Georgia location at Rich Hill is approximately 177 miles inland from the modern coastline, Veatch and Stephenson reviewed Rich Hill but in 1911 the wasn’t yet named, it was not recognized as a separate formation. They did comment that it held abundant shark’s teeth.

In several locations it overlies kaolin deposits; it is frequently exposed during kaolin mining operations. Surface exposures are very rare but do occur in Houston County.

In 1970 Sam Pickering surveyed the Clinchfield Formation in Middle Georgia and also commented that it was rich in vertebrate fossils. He assigned the name Clinchfield Sand following a 1965 oral report from Dr. Michael Voorhies, a paleontologist with the University of Georgia at the time whose work we’ve reviewed.

Previous to this the formation had been referred to as the Gosport Sand by work done in 1943 and referenced to sediments in Alabama. Pickering and Voorhies disagreed with the Gopsort correlation with Alabama and raised the Clinchfield Sand to independent formation status.

Later, in 1986 Paul Huddlestun revised this and changed the name to the Clinchfield Formation, then subdivided that into the current four variants.

In 2005 Dr. Dennis Parmley at Georgia College’s Natural History Museum surveyed the Clinchfield Formation’s vertebrate fossils in the inactive Hardie Mine kaolin quarry near Gordon, Georgia. 

His research produced several scientifically important fossils including thousands of shark’s teeth; several species of turtle shell fossils, the oldest North American colubrid constrictor family of snake, extinct members of the boa constrictor and anaconda families with both adults and young present; individual vertebra fossils were found from adults suggesting snake lengths of 15ft. 
​
Georgia Auk
Dr. Parmley’s research also produced an unusual bird fossil, a single small humerus (leg bone). Dr. Robert Chandler, also from Georgia College, was asked to share his expertise in bird evolution in reviewing this specimen.

The humerus Dr. Parmley recovered turned out to be from the oldest known North American auk. This was surprising since all specimens from this mine in Gordon are warm climate, even subtropical animals. Up until the discovery of this bone it had been thought that auks must have evolved in cold water environments. 

Auks are small diving birds which swim with their wings; flying over the waves the spot their prey, dive into the sea and pursue. It was believed that birds which swim with their wings had to evolve in cold waters where fish could not swim as fast as they can in warm waters. 

The presence of this Georgia auk bone in a tropical or sub-tropical environment has forced a re-think of the evolution of auks; perhaps all bird which swim with their wings. 
Brontothere
Parmley’s research also produced Georgia’s first brontothere fossil (meaning thunder beast, also known as a titanothere).

This was a large, rhinoceros-like land mammal related to horses. Imagine a rhino with a v-shaped horn on its snout. (Though in truth it was not a horn but a bony extension of the skull covered in skin.) 

Brontothere fossils are well known from South Dakota and Nebraska where large herds were killed off quickly by volcanic eruptions and left an extensive fossil record, butthey were unknown in Georgia until this find. 

I would like to thank the artists Quentin Lonon for this 2011 reconstruction for family Brontotheriidae, genus Megacerops though which genus or species occurred in the Clinchfield Formation is unknown. As seen, this was a large animal which was widespread in North America during the Late Eocene Epoch (say 33 to 40 million years ago) but did not did not survive the global climate change and extinction event which began the Oligocene. As a grazer, it’s believed that the tender grasses which fed large herds of these animals died back during the drier, cooler opening phases of the Oligocene and led to the extinction of the animal.

The wealth of fossils from the Gordon, Georgia area allows the reconstruction of a warm coastal Georgia environment from 35 million years ago, 155 miles inland from the nearest modern shoreline. 

​
Reported Clinchfield Formation Vertebrates:
(*) After species name notes 1970 reports from Sam Pickering 
All others are from 2005 & reported by Dr. Dennis Parmley and David J. Cicimurri. Dr. Parmley and David Cicimurri included tooth counts in their paper. (Source: Late Eocene Sharks of the Hardie Mine Local Fauna of Wilkinson County, Georgia. Georgia Journal of Science, 2003
​

Genus &/or Species             Common name                    Frequency
Lamna appendiculata *      Mackerel shark                   Common
Carcharias cuspidate*        Great White Shark              Abundant
Galecerdo latidens*             Tiger Shark                           Abundant
Sphyrna (sp?)*                     Hammerhead                       Rare
Myliobatis (sp?)*                 Eagle Ray                              Abundant
Pristis (sp?)*                         Sawfish                                  Very rare
Abdounia enniskilleni         Extinct Gray Shark             589 Teeth
Carcharias acutissima        Sand Tiger Shark                446 Teeth
Carcharocles angustidens  Megatooth Shark                2 Teeth
Carcharias hopei                 Sand/Tiger Shark                296 Teeth
Carcharias koerti                 Sand/Tiger Shark               123 teeth
Edaphodon (species?)         1st SE Chimaera                  Very Rare
Galeocerdo alabamensis    Requiem Shark                    351 Teeth
Hemipristis curvatus          Snaggletooth Shark            635 Teeth
Heterodontus                       Angel Shark                          1 Tooth
Isurus praecursor                Mako Shark                         27 Teeth
Mustelus vanderhoefti (?) Smoothhound Shark          3 Teeth
Nebrius thielensis                Nurse Shark                        79 Teeth
Negaprion eurybathrodon Lemon Shark                     2127 Teeth
Palaeorhincodon                 Whale Shark                        1 tooth
Physogaleus secundus        Sharpnosed Shark             70 Teeth
Scyliorhinus gilberti           Catshark                               53 Teeth
Squatina prima                    Angel Shark                        6 Teeth
Striatolamia macrota         Sand Shark                          1 Tooth
Basilosaurus (sp?)*             Early Whale, Large            Rare
Zygorhiza*                            Early Whale, Smaller         Rare       
Eosiren (sp?)*                       Manatee                               Common
Family; Brontotherid         Rhino-like mammal            Very Rare
Family: Alcidae                    Bird; Auk                              Very Rare
Family: Cheloniidae            Sea Turtles                           Rare
Family: Trionychinae         Soft Shelled Turtles            Rare
Dermochelydidae (sp?)      Leather Back Turtles         Rare 
Nebraskophis (new Sp?)    NA Colubrid Snake            Very Rare
Palaeophis (species?)          Palaeophid Snake              Rare
Palaeophis africanus          Large Constrictor Snake   Very Rare
Pterosphenus (species?)     Marine Snake                      Very Rare
Pterosphenus schucherti    Large Marine Snake           Very Rare
As a note: 
Pickering’s 1970 report (page 20) included finding specimens of the mega-tooth shark, megalodon in two Eocene Epoch formations. We’ll look at this animal in more detail later. This was a mistake in identification as megalodon didn’t emerge until the Late Oligocene Epoch; millions of years after these formations had been laid down. The report is interesting in the fact that Pickering lists occurrence frequency, implying multiple specimens might have been recovered, I asked Sam Pickering about this when I visited him in 2011 but he didn’t recall how many specimens were recovered and his notes had been lost decades earlier when he left the Georgia Geologic Survey. 
I spoke with Ashley Quinn, Museum Manager at the Georgia College Natural History Museum and she led me to one of their displays explaining that there were mega-toothed sharks present in Georgia’s Eocene seas, notably Carcharodon auriculatus. The museum has one of the teeth on display; it so resembles a megalodon tooth in both size and basic shape that the author would probably make the same mistake during a field identification.

Pickering’s 1970 record for Eocene megalodon finds 
Genus &/or Species             Common       Clinchfield Form.    Tivola Limestone 
Carcharodon megalodon   Giant Shark          Rare                Very Rare
This is assumed to be
Carcharodon auriculatus   Giant Shark          Rare               Very Rare
​
Sirens (Manatees)
The siren family, of which the Florida manatee is a member, is most closely related to elephants and is also known from the Clinchfield Formation and the Tivola Limestone.

Their oldest known appearance in the fossil record comes from Jamaica about 40 million years ago with Prorastomus sirenoides, which was pig sized animal with four legs. 

By 34 million years ago the sirens had evolved into fully marine animals. By 24 million years ago their current 2 genres had emerged. Two other genres are known but extinct. The Smithsonian National Museum of Natural History holds siren fossils collected in 1935 from Houston County’s Clinchfield formation. This is of interest as during the 1980s Smithsonian researchers reviewing siren evolution would come to the University of Georgia to review manatee fossils and make an important discovery about another Eocene mammal.
​

​Tivola Limestone
The Tivola limestone is slightly younger than the Clinchfield Formation and overlies it in Houston County. It is a soft, rough, richly fossiliferous limestone occurring in outcrop or shallow subsurface deposit in Crawford, Bibb, Pulaski, Houston, Bleckley, Twiggs and Wilkinson Counties. 

It was formerly known as the Ocala Limestone. In many locations it is absent, due to erosion or non-deposition. 

The thickness, where present, can be from a few inches to more than 42 feet. 

It has been actively mined for more than a century. Fresh exposures are light tan to light gray and can be composed almost entirely bryozoan debris, sand is also often present in varying small quantities. In its purest form the limestone can be more than 93% calcium carbonate, meaning the formation is made of small marine shell debris and reacts to acid, even vinegar. 

Such bryozoan remains can be so dominant that the Tivola can become bryozoan limestone.

It darkens and hardens as it weathers and can appear as nearly black in old exposures. Echinoids in the form of abundant sand dollars occur, specifically Periarchus pileussinensis, near the top of the Tivola these echinoids can often be found in numbers, stocked in living positions like pancakes.

The Tivola is a strongly marine formation. Where the underlying Clinchfield Formation and overlying Twiggs Clay Formation are both comprised of terrestrial material deposited in a marine environment, the Tivola is almost completely made of marine material, with sand being very minor. 

It is also considered an off shore formation with sediments laid down in a high energy environment. (Large fragments are common.) In most of the Tivola’s thickness the fossils are found in all positions, and often as partial remains. This shows that they originated elsewhere and were transported and deposited by strong currents. 

Near the top a change in conditions is seen which indicates a quieting of the currents. Where echinoids occurred in all positions, now they tend to be upright and in living positions with clusters of individuals often present, suggesting that these died in their current positions.
​

Below are the Tivola Limestone vertebrate Fossil records from multiple sources;
Georgia Geologic Survey; Sam Pickering 1970 (Bulletin 81)
Genus & Species                   Common name                      Frequency
Lamna apppendiculata      Mackerel Shark                      Rare
Carcharias cuspidate          Great White                            Rare    
Galeocerdo latidens             Tiger Shark                             Rare
Carcharodon megalodon   Megatooth                               Very Rare
Myliobatis (species?)          Eagle Ray                                 Common
Basilosaurus (species?)      Early whale                             Very Rare
Siren (species?)                    Manatee (rib fragments)      Rare

Dr. Michael Voorhies University of Georgia (1982)
Genus & Species                   Common name                         Frequency
Family Entelodont                Terminator pig                          Very Rare

Smithsonian National Museum of Natural History (online catalog)
Tivola Limestone vertebrates (as Ocala Limestone in these records)
Genus & Species                   Common name        Specimen - County  Collected by
Carcharhinus (species?)     Requiem shark        Tooth - Twiggs         Bill Christy
Cretolamna (species?)        Mackerel shark        Tooth - Twiggs         Bill Christy
Galeorhinus (species?)       Hound shark              Tooth - Twiggs       Bill Christy
Hemipristis (species?)        Snaggletooth shark Tooth - Twiggs         Bill Christy
Odontaspis (species?)         Sand Shark               Tooth - Twiggs         Bill Christy
Sphyraena (species?)          Barracuda                 Tooth - Twiggs         Bill Christy
    
Smithsonian National Museum of Natural History (online catalog)
Barnwell Formation vertebrates (Land Mammal)
Genus & Species                   Common name        Specimen- County   Collected by  
Leptotragulus medius        Camelid                     Tooth & jaw-Jefferson   McCallie


Leptotragulus medius
Leptotragulus medius; this interesting report come from a time when both the Tivola Limestone & Clinchfield Formation designated as parts the Barnwell group of formations; today only the Clinchfield is considered part of the Barnwell Group with the Tivola held as parts of the Ocala Group of Florida.

Samuel W. McCallie was the Georgia State Geologist from 1908 to 1933; this was during the Stephenson and Veatch research project. McCallie collected the Leptotragulus medius from Jefferson County and gave it to the Smithsonian (specimen #PAL 244447). The material included a partial left mandible and two (forward) premolar teeth (P3 & P4). 

A member of the Protoceratidae family L. medius was an even toed ungulate; meaning that the animal walked on two hooves per foot, as do pigs, goats and deer. They were herbivores. 

They resembled deer though they were smaller and more closely related to camels. We don’t know a great deal about this particular species but the genus Leptotragulus emerged during the Eocene Epoch and went extinct with the Eocene-Oligocene extinction event, enduring for 6.3 million years (40.2 to 33.9 million years ago). Estimates put the weight for members of this genus at less than 13.6 kilograms (30 pounds) for an adult.
​

​Dry Branch Formation

The Dry Branch Formation, named for the community of Dry Branch, Georgia on the Bibb County, Twiggs County line. It consists of three distinct members; 
The Twiggs Clay
The Irwinton Sand
The Griffins Landing

As a whole the Dry Branch Formation extends from Dooly County in the southwest part of the state into the South Carolina counties of Lexington and Orangeburg; northwards to very near the Fall Line and well southward as shallow subsurface.   
​ 
Twiggs Clay Member, Dry Branch Formation
The Twiggs Clay overlies the Tivola Limestone in many parts of central Georgia; it too is Late Eocene Formation, being slightly younger than the Tivola Limestone. It is nearly pure, fine grained marine clay up to 100 feet thick in areas. It is known to bear vertebrate material, fish teeth and scales and (rarely) whale bones. Of course it was the Twiggs Clay which produced Ziggy (Dorudon serratus) at the Museum of Arts and Sciences in Macon, GA. ​
​

Irwinton Sand Member, Dry Branch Formation
This is typically a distinctly bedded sand and sand-clay sediment overlying the Twiggs Clay in Twiggs, Washington and Wilkinson Counties of Georgia. It can be fine to medium grained almost pure quartz sand. Fossils are generally rare but can be found as chert and chert cemented sandstone as well as shell fragments of clams and oysters.

Griffins Landing Member, Dry Branch Formation
This is typically a fairly well sorted, massive to vaguely and rudely bedded hardened sand seen in Burke County, Georgia as well as isolated points in parts of east-central Georgia. Limestone and clay beds occur; fossils include oysters shell beds (Crassostrea gigantissiam) and other shells.

Generally speaking these divisions of the Dry Branch Formation weren’t recognized historically and fossils in collections labeled as Twiggs Clay probably originated from the Twiggs Clay Member of Dry Branch Formation. 

Specimens from the Irwinton Sand and Griffins Landing Members would have been specified as Late Eocene undifferentiated or residuum.
​

Twiggs Clay Vertebrate Species
Twiggs Clay Vertebrates reported in 1970 by Sam Pickering (Bulletin 81)
Genus & Species                   Common name                    Frequency
Lamna apppendiculata      Mackerel Shark                    Common
Carcharias cuspidate          Great White (Warm Seas) Abundant
Galeocerdo latidens              Tiger Shark                          Common
Myliobatis (species?)            Eagle Ray                             Abundant
Basilosaurus (species?)        Early whale                         Very Rare
Eosiren (species?)                  Manatee                               Rare

Dr. Dennis Parmley at Georgia College and State University adds:
Genus & Species                   Common name                    Frequency
Carcharocles auriculatus   Megatooth Shark                 Rare

The author (Thomas Thurman) adds:
Genus & Species                   Common name                    Frequency
Ptychodus (species?)            Extinct Ray-like Shark       Rare
              (Observed in road cut along Elko Road in Houston County.)

The American Museum of Natural History (AMNH) in New York maintains a national online catalog of vertebrate species. For the Twiggs Clay the AMNH lists:
Location: Huber Mine (Now KaMin) Huber Pit #1 
Genus & Species                   Common name        Finds                    Reported
Lamna twiggsensis              Mackerel shark        2 teeth                Gerard R. Case
Ginglymostoma obliquum  Nurse shark              2 teeth                Gerard R. Case
Odontaspis acutissima        Sand shark                3 teeth                 Gerard R. Case         
Propristis schweinfurthi     Sawfish                      3 snout teeth      Gerard R. Case
Myliobatis (species?)           Eagle Ray                   8 teeth                 Gerard R. Case


Location: Huber Mine (Now KaMin) Huber Pit #2
Genus & Species                               Common name        Finds              Reported by
Scyliorhinus enniskilleni                Catshark                    10 teeth         Gerard R. Case
Hemipristis wyattdurhami           Snaggletooth shark 5 teeth            Gerard R. Case
Negaprion eurybathrodon             Requiem shark        5 teeth            Gerard R. Case  

The AMNH also list for Huber (No pit location given):
Genus & Species                   Common name        Finds           Catalog# 
Pterosphenus (species?)     Constrictor snake    Vertebra        FR 7167

 
Ocmulgee Formation
The Ocmulgee Formation frequently occurs directly on top of the Twiggs Clay Member of the Dry Branch Formation but it’s a little sporadic in appearance. Sam Pickering knew this as the Cooper Marl in his 1970 survey; that name has been overturned and the Ocmulgee Formation is now accepted. 

Considered to a near shore formation the Ocmulgee is a sandy, glauconitic (glauconite; a green clay mineral containing iron & potassium) limestone. It is highly variable and much harder than the more frequently exposed Tivola. 

Typically it is composed of alternating beds, varying in thickness, of hard and soft limestone, overall the formation ranges up t0 15 meters (50ft) thick. It is typically fossiliferous throughout with many layers being highly fossiliferous with invertebrates in living positions. The sandier portions tend to be less fossiliferous, though the author has collected crab claws and sand dollars even from these.
         
With the Ocmulgee Formation we are looking at the uppermost Eocene Epoch exposure of the Coastal Plain. Climbing up through the Coastal Plain sediments the next formation would belong to the Oligocene Epoch.     

​Sam Pickering reported the below Ocmulgee vertebrate occurrences: 

Ocmulgee Formation Vertebrates reported in 1970 by Sam Pickering (Bulletin 81)

Genus & Species                   Common name                 Frequency
Lamna apppendiculata      Mackerel Shark                 Rare
Carcharias cuspidate          Great White                       Common
Galeocerdo latidens             Tiger Shark                        Rare
Myliobatis (species?)           Eagle Ray                           Abundant

​
​Smithsonian; Eocene
The below files lack detailed stratigraphic location so they are presented here, many of the records are also repetitive, the same species collected at different times by different researchers, so here they are consolidated to present a record of what’s present in Georgia’s Eocene sediments:
​Genus & Species                   Common name                 Frequency
Lamna apppendiculata      Mackerel Shark                 Rare
Carcharias cuspidate          Great White                       Common
Galeocerdo latidens             Tiger Shark                        Rare
Myliobatis (species?)           Eagle Ray                           Abundant


Smithsonian National Museum of Natural History 
Eocene Vertebrates from Georgia
Online Catalog: Search the Department of Paleobiology Collections
Downloaded: 7/April/2013

Genus & Species                   Common name        Location                    Specimen
Order: Testudines               Turtle                         Wilkinson County   34 shell frag.
Family: Mesonychidae       Mesonychid              Crisp County             Partial Femur
Propristis schweinfurthi    Sawfish                      Bibb County             Dermal bones
Protosiren (species?)          Siren/Manatee         Houston County      Partial rib
Smithsonian National Museum of Natural History 
Eocene Vertebrates from Georgia
Online Catalog: Search the Department of Paleobiology Collections
Downloaded: 7/April/2013

Genus & Species                   Common name           Location                            Specimen
Order: Testudines               Turtle                        Wilkinson County         34 shell frag.
Family: Mesonychidae       Mesonychid             Crisp County                  Partial Femur

Propristis schweinfurthi     Sawfish                    Bibb County                   Dermal bones
Protosiren (species?)          Siren/Manatee       Houston County            Partial rib
Mesonychids are essentially medium to large hoofed predators. The earliest species walked flat on their toes, by the Late Eocene they likely walked on hooves. Called wolves-with-hooves they were effective predators, probably capable of taking large prey and were adapted to running. 

This is the only report of mesonychids in Georgia which the author has seen. Several species are known through North America. Mesonychids emerged in the Paleocene Epoch 55 to 60 million years ago but went extinct in the Early Oligocene around 33 million years ago.

 
References:
·         Upper Eocene Stratigraphy of Central and Eastern Georgia. Paul F. Huddlestun and John H. Hetrick. Bulletin 95. Georgia Geologic Survey. 1986
·         Stratigraphy, Paleontology and Economic Geology of Portions of Perry and Cochran Quadrangles, Georgia. Sam M. Pickering Jr. Bulletin 81. Georgia Geological Survey. 1970
·         Late Eocene Sharks of the Hardie Mine Local Fauna of Wilkinson County, Georgia. Dennis Parmley, David J. Cicimurri. Georgia Journal of Science, Vol.61, Pgs 153-179, 2003. Georgia Academy of Sciences
·         Diverse Turtle Fauna from the Late Eocene of Georgia Including the Oldest Records of Aquatic Testudinoids in Southeastern North America. Dennis Parmley, J. Howard Hutchinson and James F. Parham. Journal of Herpetology, Vol. 43, No.3, Pgs. 343-350. 2006. Society for the Study of Amphibians and Reptiles.
·         Size and Age Class estimates of North American Eocene Palaeopheid Snakes. Dennis Parmley & Harold W. Reed. Georgia Journal of Science, Vol. 61, pgs. 220-232. Georgia Academy of Sciences.
·         Nebraskophis Holman From The Late Eocene of Georgia (USA), the Oldest Known North American Colubrid Snake. Pennis Parmley and J. Alan Holman. Acta Zoologica Cracoviensai Vol. 46, pgs. 1-8, 2003
·         First Record of a Chimaeroid Fish from the Eocene of the Southeastern United States. Dennis Parmley and David J. Cicimurri. Journal of Paleontology, Vol.79. pgs, 1219-1221. 2005 The Paleontological Society.
·         Palaeopheid Snakes from the late Eocene Hardie Mine Local fauna of Central Georgia. Dennis Parmley and Melanie DeVore. Southeastern Naturalist, Vol.4, No.4, pgs. 703-722. 2005.