How can scientists tell how old animals are?

Question

For example, how do they know the Greenland shark is 512 years old (believed)?

In: Biology

Answer 1

In living animals, age can be estimated off things like bone density/growth plate fusion, how worn teeth are, in animals like tortoises that have shells, the shells have rings like a tree so can be counted, general size of an animal, and extrapolation from known ages of other animals of similar type. Like if there’s a great white shark that’s 15 feet long and is known to be 30 years old, and was known to grow about 6 inches a year (all numbers hypothetical), and then another shark is seen that’s 25 feet long, an age can be estimated from the average.