Belemnite mollusc rostrum fossil. Belemnites were marine animals that were abundant in the the Jurassic and Cretaceous periods, 201-66 million years ago. Their closest living relatives are squid and cuttlefish. They had a squid-like body but, unlike modern squid, they had a hard internal skeleton. In the animals tail, the skeleton formed a bullet-shaped feature referred to as a rostrum. These are the parts that are normally found as fossils. Found in Holzmaden, Germany.