Pterosaur fossils are divided into two broad categories: Rhamphorhynchoid and Pterodactyloid. The former are often easily distinguished by a longer tail, but the way that the skull connects to the vertebrae also distinguishes these two types of pterosaur. A few researchers, including John Goertzen,believe that at least one species of Rhamphorhynchoid survived until at least the 17th Century. Standard models of biology (based upon naturalism philosophy rather than scripture) include the assertion that the last species of pterosaurs became extinct about 65 million years ago; this is disputed by some creationist cryptozoologists who believe that Rhamphorhynchoids still live in some areas, especially in the southwest Pacific.