As you probably already know, there are two groups of turtles that belong to the superfamily Chelydroidea:
common snapping turtles and alligator snapping turtles. Both groups have that distinct prehistoric look and feel to
them and are quite often confused for each other. However, there are significant differences between the two which are easy to spot,
even to an untrained eye.
Common snapping turtle (left) and alligator snapping turtle (right)
Common snapping turtle - Chelydra serpentina
Alligator snapping turtle - Macroclemys temmincki
The shell of the common snapper seems to be quite smooth, especially in larger individuals, while the alligator snapper's shell has easily distinguishable individual scutes with a distinctly bumpy feel. Although the alligator snapper's shell also becomes smoother with age, the 'rougher' feel never really goes away.
Common snapping turtle - side view
Alligator snapping turtle - side view
The shell of alligator snapping turtle has three distinctive ridges, while the common snapper's shells are smoother.
You can also see the difference in the shape of their heads, as you look at them from above. The alligator snapper has a triangular, pointed head, while the common snapper's head is more oval.
Common snapping turtle - carapace
Alligator snapping turtle - carapace
One of the most distinctive features of the alligator snapping turtle is the fleshy lure located at the bottom of its mouth, easily spotted when the turtle opens its jaws. The alligator snapper is the only turtle in the world with such a 'device'. With its jaws open the turtle fools fish into believing its lure is a live worm. Once a fish enters this trap to take a bite - it becomes a meal itself. The common snapper does not have such a lure.
Alligator snapping turtle - easily visible red fleshy worm-like lure in the mouth
Another unique feature found on the alligator snapping turtle is a fleshy eyelash-like growth around its eyes - again, the common snapping turtle lacks them.
Alligator snapping turtle - eye with fleshy 'eyelashes' clearly visible
Common snapping turtle - eye, no 'eyelashes'