Stylemys Tortoises
Tortoises and turtles
One of the most familiar and commonly preserved fossils in the White River Badlands are those of the land tortoises. Common in many levels, the best preserved and most commonly found one are in the oreodont beds of the Orellan NAMLA. Chadronian age specimens tend to be broken. Fossil land tortoises typically range in size from a few inches to as much as two feet in length, with the average size being 10 - 12 inches long. Due to the shape and structure of the shell, it is clear that they were land tortoises. Skeletal remains are also common although shells containing complete skeletons and the tortoise's skull are relatively rare. Fossils believed to be tortoise eggs are also commonly found.
The most common variety of tortoise found is that of Stylemys nebrascensis, but other chelonians are occasionally found. Aquatic turtles are far rarer in White River formations. Although many collectors and paleontologists casually lump all Chadronian/Orellan tortoises into a single species, Stylemys nebrascensis, a number of paleoherpetologists now question this, feeling that based on shell shape, and even after taking post mortem shell deformation into consideration, that some species were relatively flat like our modern gopher tortoise of the Southeast and Southwest, while others were round and probably did not borrow. Similar niche separation is commonly observed in land tortoises of Africa and Asia.
The abundance of high quality mammal fossils in the White River Badlands is felt by many specialists to be related to den use by these animals. Fine, articulated oreodonts and nimravids are especially common in these formations but would not be had they died in the open. Using the modern gopher tortoise of the southeastern states as an example, it has been observed that many unrelated species of animals, including rabbits, foxes, opossums, raccoons, bobcats, both venomous and non-venomous snakes and raccoons live in the dens of tortoises, sometimes while the tortoise is also present. The occurrence of such mutually beneficial behavior during the Orellan NALMA would help explain the presence of some many articulated skeletons of oreodonts and medium-sized predators. Following the death of these mammals, their remains would have been quickly covered up when the burrows were flooded, thus setting the state for future, museum-quality specimens to be found millions of years later.
Written by Alan S
The most common variety of tortoise found is that of Stylemys nebrascensis, but other chelonians are occasionally found. Aquatic turtles are far rarer in White River formations. Although many collectors and paleontologists casually lump all Chadronian/Orellan tortoises into a single species, Stylemys nebrascensis, a number of paleoherpetologists now question this, feeling that based on shell shape, and even after taking post mortem shell deformation into consideration, that some species were relatively flat like our modern gopher tortoise of the Southeast and Southwest, while others were round and probably did not borrow. Similar niche separation is commonly observed in land tortoises of Africa and Asia.
The abundance of high quality mammal fossils in the White River Badlands is felt by many specialists to be related to den use by these animals. Fine, articulated oreodonts and nimravids are especially common in these formations but would not be had they died in the open. Using the modern gopher tortoise of the southeastern states as an example, it has been observed that many unrelated species of animals, including rabbits, foxes, opossums, raccoons, bobcats, both venomous and non-venomous snakes and raccoons live in the dens of tortoises, sometimes while the tortoise is also present. The occurrence of such mutually beneficial behavior during the Orellan NALMA would help explain the presence of some many articulated skeletons of oreodonts and medium-sized predators. Following the death of these mammals, their remains would have been quickly covered up when the burrows were flooded, thus setting the state for future, museum-quality specimens to be found millions of years later.
Written by Alan S
Taxa of turtles ranked by abundance
Stylemys nebrascensis
Testudo sp.
OBSOLETE TAXA
Graptemys inornata, Testudo brontops, Xenochelys (Lower zone, Titanothere zone)
Testudo laticunea, T. thomsoni (Middle to upper Oligocene)
Testudo sp.
OBSOLETE TAXA
Graptemys inornata, Testudo brontops, Xenochelys (Lower zone, Titanothere zone)
Testudo laticunea, T. thomsoni (Middle to upper Oligocene)