The animal with the longest lifespan is the Greenland shark (Somniosus microcephalus). These sharks have been found to live exceptionally long lives, with some individuals estimated to exceed 400 years in age. Determining the precise lifespan of Greenland sharks is challenging due to their slow growth rate and difficulties in studying them. Scientists use various techniques, such as radiocarbon dating of eye tissue and the presence of specific chemical markers, to estimate their age. Other long-lived animals include the bowhead whale, which can live over 200 years, and certain species of tortoises, such as the Galapagos tortoise, which can live well over 100 years. However, the Greenland shark holds the record for the longest-known lifespan among animals.