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​14M:
Eocene Terrestrial Mammals
From
Gordon; Georgia


A review by
Thomas Thurman
Posted 08/December/2019
 
​

Picture
​Paleontology is alive and well at Georgia College in Milledgeville. In 2019 Parker D. Rhinehart published a paper revealing 4 previously unreported terrestrial mammal species from Hardie Mine; Alfred J. Mead and Dennis Parmley stood as co-authors. (1)
 
Wilkinson County’s Hardie Mine is an inactive kaolin mine just north of Gordon, Georgia in Wilkinson County. It has been a treasure trove of Eocene Fossils and previous work from Georgia College has done a splendid job of collecting, researching and publishing these finds.
​

​The fossils come from a spoil pile of the Clinchfield Formation near the north wall of mine pit. At the wall the Clinchfield Formation occurs as a bed approximately 1 meter (3.28ft) thick underlain by kaolin deposits and overlain by non-fossiliferous Twiggs Clay.
 
Rhinehart reports a Daphoenus (bear dog) species unknown, a Palaeolagus temnodon (rabbit), Megacerops (brontothere) species unknown, and Hyracodon (hornless rhino) species unknown.
 
You no doubt noticed they’re all teeth. Tooth enamel is the hardest substance the body creates and the one which is most easily preserved as fossils.


Picture
Daphoenus (bear dog)
The canine tooth shown was compared to Daphoenus and Hyaenodon mustelinus (Hyena-tooth) specimens from Badlands National Park and held in the Georgia College vertebrate paleontology collections. The size and dimensions of the tooth clearly identified it as a bear-dog.
​
Picture
Daphoenus from Wikipedia:
“Daphoenus, like the rest of its family, was called a "bear dog" because it had characteristics of both bears and dogs. These animals were about the size of the present-day coyote. Daphoenus vetus was the largest species. The male skulls could reach up to 20 centimetres (7.9 in) in length. Daphoenus had short legs and could only make quick sprints; it was not capable of running long distances. It is thought that these animals ambushed their prey and did some scavenging. Fossil footprints suggested that, like present-day bears, these animals walked in a flat-footed way. Daphoenus dug burrows for their offspring to stay in and hide from their prey.”
 
To quote Rhinehart’s paper;
“The Hardie Mine specimen represents the first known occurrence of Daphoenus in the southeastern United States.”
​

Picture
Palaeolagus temnodon (rabbit or hare)
A cheek tooth from the lower law, as imaged, was recovered from the Hardie Mine sediments which lived near Gordon, Georgia 35 million years ago. The tooth was identified by comparison with specimens in the Georgia College collection from Badlands National Park in South Dakota.
​

Picture
This ancient hare, like modern hare, lived in a savannah, plain or woodland between fertile lands of the paleo-Ocmulgee and paleo-Oconee Rivers. No doubt it hid whenever it sensed the presence of bear-dogs.
 
The genus Palaeolagus lacked the highly developed hind legs which modern rabbits and hares enjoy, so it wasn’t fast by today’s standards. But, as we’ve discussed, neither was the bear-dog Daphoenus. It may well be that speed, or bursts of speed, evolved together in both prey and predators. Any advantage, no matter how small, which encourages survival and reproduction in an individual is both copied and magnified in successive generations.
 
There’s another important fact about this tooth from Palaeolagus temnodon. To quote Rhinehart’s paper;
“The Hardie Mine specimen represents the first known occurrence of Palaeolagus in the southeastern United States.”
​
Picture
​Megacerops (brontothere)
An almost complete Megacerops tooth was reported in the paper, a right molar.
​
Picture
​The Hardie Mine specimen represents the first known occurrence of Megacerops in the Late Eocene sediments of the southeastern United States. Though resembling a modern rhinoceros these were closer to elephant sized animals. All species and both sexes carried horns on the end of their snout, though the horns of males were much larger than females which suggests they were social animals and there was likely combat for mating rights.
​

To quote Rhinehart;
“…the Hardie Mine specimen represents the first known occurrence of Megacerops in the Late Eocene sediments of the southeastern United States.”
​
Picture
Hyracodon (hornless rhino)
Hyracodon looks somewhat like a horse, or a pony at first glance, but is in reality related to rhinoceroses. It has been described as a hornless, agile-built rhino with three toes on each foot. It was adapted towards running and was likely a browser.
​

Picture
The recovered tooth, though partial, shows the diagnostic characteristics of a Hyracodon. This Hardie Mine specimen represents the first known occurrence of Hyracodon in the southeastern United States.
 
All four of these species are fairly common in western North America but rare in the Southeast, this shows that many species were likely widespread so the hunt for fossils should continue.
​

Historically, the Clinchfiled Formation is Georgia's richest source of Cenozoic vertebrate fossils, below is a partial list with these 2019 reports added.
​

​Genus &/or Species        Common name         Frequency
Fish (sharks)
Lamna Appendiculate *       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           Extremely 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

Mammals
Basilosaurus (sp?)*                 Early Whale, Large       Rare
Zygorhiza*                                Early Whale, Smaller    Rare      
Eosiren (sp?)*                           Manatee                          Common
Family; Brontotherid               Rhino-like mammal     Very Rare
Daphoenus                                 Bear-dog                         Very rare (2019)
Palaeolagus temnodon            Rabbit or hare               Very rare (2019)
Megacerops (sp)                        Rhino-like animal         Very rare (2019)
Hyracodon                                  Hornless rhino               Very rare (2019)        


​Reptiles
Family: Cheloniidae                   Sea Turtles                   Rare
Family: Trionychinae                Soft Shelled Turtles    Rare
Dermochelydidae (sp?)            Leather Back Turtles  Rare
Nebraskophis (new Sp?)          Colubrid Snake             Very Rare
Palaeophis (species?)                Palaeophid Snake        Rare
Palaeophis africanus                 Constrictor Snake       Very Rare
Pterosphenus (species?)            Pterosphenus Snake  Very Rare
Pterosphenus schucherti           Constrictor Snake       Very Rare
​Congratulations to Rhinehart, Meade and Parmley on the publication of their paper and a hearty thanks to them for expanding our knowledge of Georgia’s Fossil record. 
​ 

​References
  1. Rhinehart, Parker, D.; Mead, Alfred J.; Parmley, Dennis; Eocene Terrestrial Mammals from Central Georgia; Volume 77 No. 2, Article 6, Georgia Journal of Science, 2019