What is the fine-grained topic of the following text: Megalosaurus had been discovered around 1815 and announced in 1824, but the finder, William Buckland, had only a piece of the lower jaw and a few leg bones, and he was just speculating when he surmised that the fossils came from a forty-foot long Mesozoic lizard. Only return the topic.
Discovery and speculation about Megalosaurus fossils by William Buckland