Of Tortois and Turtles
Tortoises live on the land, whereas turtles live in the water. Their anatomy is adapted to their way of life, and by this they can be easily distinguished from each other. The shell of tortoises is very convex, heavy and completely ossified, whereas the shell of turtles is more flattened and incompletely ossified. Another difference between tortoises and turtles is the shape of their feet. Tortoises have short, club-shaped feet with blunt claws, whereas turtles have more mobile limbs with distinct digits and sharp claws, united with a web. Sea turtles are more typical than freshwater and swamp turtles, which are actually closely related to the tortoises whereas the sea turtles are not.

 

A tortoise with convex shell and broad feet.
Testudo hipparionum from China.

 

A turtle with flattened shel and winged feet.
Photograph Janet Kamphorst.