I would wager that the oldest wild animal in almost every state in the lower 48 is some sort of turtle, but knowing exactly how long they can live is a fairly tricky matter to resolve. Wood Turtles (Glyptemys insculpta), for example, have been confirmed up to at least 55 years of age in the wild, but experts agree that is likely nowhere near their actual potential longevity. To determine that, a biologist first needs to find a turtle when it is young enough to age with confidence. Because Wood Turtles develop annual growth rings (annuli) on their shells, you can do that for about the first 20 years of their life, after which point they stop growing*. Then the turtle needs to be marked in a way that will allow a future biologist to identify that same turtle (usually through notches filed into the edge of the shell). Finally, that future biologist needs to capture that same turtle 50 or more years later, recognize the shell notches, look up the original data (if it still exists), and then look for a matching notch code with a corresponding age. That does not happen very often, but that is how we know Wood Turtles can survive at least into their 50s (turtles marked as adults in the 1970s were recaptured in 2012-2013).