The Choctaw Sea was a Cenozoic eutropical subsea, which along with the Okeechobean Sea, occupied the eastern Gulf of Mexico basin system bounding Florida. Location The Choctaw Sea was named for the Choctaw or Choctawhatchee River of northern Oligocene Florida. It occupied most of the Florida Panhandle including the river deltas of the Choctawhatchee River, Apalachicola River, and Ochlockonee River. At its maximum coverage it encompassed an area as far north as the city of Bainbridge in Southwest Georgia and as far to the southeast as Taylor County, Florida, United States. The Choctaw Sea was divided further into two groups of three subseas based upon marine fauna. These subseas were named: Bainbridge Subsea Chattahoochie Subsea Chipola Subsea Walton Subsea Alaqua Subsea Jackson Subsea Subseas Bainbridge Subsea Period: Oligocene. Geologic stage: Rupelian through early Chattian. ~33.9—28.4 Ma (beginning approximately ). Animal age: Orellan through Geringian. ~33.9—26.3 Ma. Post-Bainbridge dry period: Chattian ~28.4—23.03 Ma. The Bainbridge Subsea was named for the fossil beds of Bainbridge, Georgia and is the oldest subsea. This period spanned the existence of the Gulf Trough between Georgia and Florida's Orange Island. It was a warm but cooling climate, moving towards an ice age. The Suwannee Limestone was established during this time. Basilosaurus cetoides and Zygorhiza, early toothed whales, as well as Protosiren, an extinct ancestor of the Manatee, inhabit these waters and are the earliest mammal fossils uncovered with specimens from Citrus County in dolomite ~40—37 Ma. and Marion County, Florida dating from 37.2—33.9 Ma. Chattahoochee Subsea Period: Miocene. Geologic stage: Late Chattian through early Aquitanian ~28.4—23.03 Ma., approximately . Animal age: Arikareean. ~30.8—20.6 Ma. Post-Chattahoochee dry period: Late Aquitanian through early Burdigian ~23.0—20.5 Ma. The Chattahoochee Subsea was named for the Chattahoochee Formation which formed during the rise in sea level. The Chattahoochie Subsea was much smaller in size than the Bainbridge and during the filling of the Chattahoochee, the St. Marks Formation of limestone and sand was established. The Gulf Trough closed between Georgia and Florida forming the complete Florida peninsula allowing land animals to move southward. The fossil record shows that land animals entered the newly formed peninsula ~24.8 Ma. Chipola Subsea Period: Miocene. Stage: Early Burdigalian through the late Langhian ~20.43—15.97 Ma., approximately . Animal age: Hemingfordian through Barstovian ~20.3—13.6 Ma. Post-Chipola dry period: Early Serravallian ~13.65—12.0 Ma. The Chipola Subsea was named after the Chipola Formation and was formerly known as the