Pirates on Dinosaur Island -- Mark Edwards, Paperback

Dr. Christopher Lemuel escapes England on a privateer after he has the misfortune of winning a duel. With his life in jeopardy, he signs on as ship's doctor only to face further dangers on the high seas. The good doctor is wounded in a sea battle, captured by pirates, and reluctantly becomes a buccaneer.

Then matters become stranger still when Dr. Lemuel is marooned on an island populated by enormous beasts unknown in natural history.