Palaeontologists believe that internal fertilisation evolved around 400 million years ago, so anything this old is literally old as fuck.

Also, the first animal in the fossil record known to reproduce this way is an extinct species of fish, amusingly named Michrobrachius dicki.

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The oldest known mammal species to evolve on Earth was a small shrew-like creature known as Juramaia sinensis which lived about 160 million years ago. Descended testicles are a mammalian trait thought to have been present in the earliest mammal species. So it's quite likely that anything 160 million years old is literally old as balls.

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