A unicorn, a dinosaur, and a shark were riding a bicycle

"According to the narrator of this book, a unicorn, a dinosaur, and a shark were riding a bicycle. But they say that's not true, and they just want to take a load off for once. They're tired of being told what to do by the bossy storyteller! And who is a reader supposed to believe, anyway--a book's narrator or its characters?"--Book jacket.