Many characteristics of snapping turtles also occur in other turtle species, so it's important to consider several different features, such as size and shape of the head and shell, to ensure a positive identification. It can be challenging for novices to distinguish the two different types of snapping turtle -- common snappers and alligator snappers -- from each other, but it is relatively easy to learn how to distinguish them from all other turtles.
Most snapping turtles are sexually mature by 8 to 10 years of age, by which time they have reached at least 12 inches in shell length. Few other North American species commonly reach such sizes, except large softshell turtles, which are easy to identify by noting their leathery shells. While size is only a helpful characteristic for identifying adult snapping turtles, plenty of other characteristics can help you identify young specimens.
All snapping turtles have noticeably long tails, often with a spiky ridge extending down their length. When compared with other turtles, it is obvious that snapping turtle tails are unusually long. Like most aquatic turtles, male snapping turtles possess longer, thicker tails than females do. Additionally, the vents of male snapping turtles are situated close to the tip of the tail, while the vents of females are located near the base of the tail.
Shape of the Shell and Skull
Snapping turtles have enormous heads. In fact, this is one of the most obvious features common to all members of the family Chelydridae. Additionally, while most turtles have keratinous beaks (technically called rhamphothecae), snapping turtles have very distinctive, hooked upper beaks.
Snapping turtles have small shells relative to their size. Many observers note that their shells look much too small for such large turtles. Because of the small size of their shells, snapping turtles cannot completely withdraw into their shells. All snapping turtles possess keeled shells while young, meaning that they have raised rows of scutes on their carapaces. However, as they grow, some snapping turtles lose these ridges.
Common Snappers vs. Alligator Snapping Turtles
Scientists recognize two different snapping turtle species. Common snapping turtles (Chelydra serpentina) range over a much larger area, are incredibly adaptable and thrive in a variety of water bodies, including swamps, ponds, rivers and reservoirs – a few scattered populations even inhabit brackish water. Members of the other described species – alligator snapping turtles (Macrochelys temminckii) – attain much larger sizes than do common snapping turtles, have much larger heads than do their relatives, and are more selective in their habitat choices.
To distinguish mature common snapping turtles from mature alligator snapping turtles, simply note the presence or absence of three distinct keels on the carapace. Alligator snapping turtles retain these keels for the duration of their lives, while common snapping turtle shells become smooth as they age.
The tongues of these animals offer another distinguishing characteristic. While common snapping turtles have muscular tongues, which appear relatively normal by chelonian standards, alligator snapping turtles have small, cylindrical, red tongues, which they use as a lure while hunting for fish underwater.