You might have seen these animals, but you've unlikely imagined they could be millions of years old! Tuatara might look like a regular iguana at first, but it’s literally a living fossil since it’s been around for about 250 million years. Jellyfish have been present on our planet for over 500 million years. Chinese Giant Salamander can grow to be bigger than an adult person, and it's been roaming our planet for 170 million years already. The sea lamprey is ancient parasitic fish that lives in the western and northern Atlantic Ocean.