The family Kinosternidae consists of two genera and twenty three species. Four species belong to the genus Sternotherus (musk turtles), and nineteen belong to the genus Kinosternon (mud turtles). The family Kinosternidae is distributed from southeastern Canada to the United States east of the Rockies and southward to Brazil. These are small turtles, with the largest species in Texas achieving a maximum length close to 7 inches (17.8 cm).
Members of this family are aquatic and sometimes seen patrolling the bottoms of brackish marshes, creeks, flooded fields, lakes, ponds, and rivers. Mud and musk turtles engage in moderate amounts of basking. However, because the turtles’ lifestyle causes significant algae growth on their shells, observers occasionally mistake an algae-covered turtle for a rock. Kinosternid turtles are capable of remaining submerged underwater without surfacing for several minutes. Their underwater ability is due in a large part to buccopharyngeal respiration.
Mud and musk turtles have a carapace that is oval-shaped and has twenty-three marginal scutes including the cervical scute. The plastron has ten to eleven scutes and may have a flexible hinge.
As evidenced by fossil material, the family Kinosternidae has been around for a long time. A fossil of Xenochelys formosa was discovered in deposits in South Dakota that dated to the Oligocene Epoch (23 million to 38 million years ago). This specimen is the oldest known representative of the family.
2 genera and 5 species of kinosternid turtles are found in Texas.