For hundreds of years, sea monsters have appeared on maps — both as warning to travelers and as decoration. Scholar Chet Van Duzer explores these beasties in his new book, Sea Monsters on Medieval and Renaissance Maps ($22 and up, amazon.com), and gives readers a better understanding of their place and purpose in history.

“The ocean has had a spell on me since I was a child, and I have been studying old maps for the past 15 years,” Van Duzer explains. “In 2009, I was in the National Library in Madrid. I consulted a 15th-century manuscript of Ptolemy’s Geography and saw that its maps had sea monsters everywhere. I was immediately interested.

“I started investigating the sea monsters on other medieval and Renaissance maps, and found them to be absolutely fascinating, both for their beauty and their whimsy, and for what they can tell us about the sources the cartographer was using.”

Sea Monsters on Medieval and Renaissance Maps explores how conceptions of sea monsters evolved through the years, possibly from real sightings of walruses and sharks.

“I hope that readers come away from the book with a smile inspired by images of some of the more-whimsical sea monsters,” the author says.