Belemnite
In 1826 Mary Anning discovered what appeared to be a chamber containing dried ink inside a belemnite  fossil. She showed it to her friend Elizabeth Philpot who was able to revive the ink with water, and use it to illustrate some of her own ichthyosaur fossils. Other local artists were soon doing the same when more fossilised ink chambers were discovered. Anning noted how closely the chambers resembled the ink sacs of modern squid and cuttle fish, which she had dissected to better understand the anatomy of fossil cephalopods. This led William Buckland to publish that Jurassic belemnites had used ink for defence just as many modern cephalopods do.