Turtle is aquatic or semi-aquatic animal with webbed feet. Tortoise is terrestrial animal with clubbed feet, domed shell and generally inhabiting warmer regions. Terrapin is a turtle living in fresh or brackish water. The term originally referred to the diamondback terrapin, Malaclemys terrapin. Each spring female turtles must find a suitable location to dig a nest and lay eggs and leaves them to develop and hatch on their own. During the weeks of incubation, many eggs are dug up and eaten by predators or succumb to disease. There is a marked contrast to box turtles and tortoise species, which tend to have a high, domed shell and stumpy, elaphantine feet better suited for walking around on land. A two-step model has been proposed for the evolutionary origin of the turtle shell. The carapacial ridge (CR) is critical for the entry of the ribs into the dorsal dermis. Turtle derbies have a long history in many communities in eastern, mid-western, and southern states. Turtles as well as other reptiles carry Salmonella bacteria that can make humans sick. Children younger than 5 years of age and immune-compromised persons of any age should avoid contact them.