TRIASSIC to PLEISTOCENE PERIOD: 230 million - 10,000 years ago
Turtles and land tortoises comprise the reptilian group TESTUDINIDAE. There are two North American lineages of thick-shelled land tortoises that originate from the Oligocene Period - the sub-genera Hesperotestudo and Caudochelys. Both types existed in Florida to the end of the Late Pleistocene Period when they all went extinct. The early inhabitants of what is now the southern United States coexisted with these Giant Land Tortoises and hunted them for food. These creatures cannot withstand long periods of freezing temperatures and thrive only in regions with mild winters. Despite the term "Last Ice Age" their presence in the fossil record right up to the end of the Pleistocene show that this region was not as cold during winter periods as it is today.
The oldest fossil turtles found date back to the Triassic Period in Germany with Progaochelys and Proterocheris. Before the end of the Cretaceous Period, most modern turtle groups existed with representatives in existence. Florida's oldest fossil ever found is a marine turtle dating to the Cretaceous. Portions of the creature were collected 9210 feet below the surface of Okeechobee County during well-drilling in 1955.
Turtles have highly specialized anatomy for living in their environment. The upper carapace is formed from the fusing of individual bony elements. Thoracic vertebra are fused to the inside of the upper carapace. The underside flat portion of the shell is called the PLASTRON. The overall shape of the carapace indicates the environment in which the turtle or tortoise lived in. High-domed shells indicate land-dwelling species while low-domed shells are more hydrodynamic and indicate an aquatic life. Even though the do not possess teeth, most turtles are carnivores.
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