PHOTOS: Sea Monsters Real and Imagined
"It's a mammal with a long, rat-like snout, a rather high number of small incisors, closely spaced premolars with pointed cusps, and especially long, curved upper canines. Note that, unlike dogs, foxes and so on, it doesn't have an obvious rhinarium (the area of dark, distinctly textured skin that surrounds the nostrils in such animals). These features all immediately screamed "opossum" to me. Partly this is because I've handled opossum skulls and am familiar with their surprisingly big upper canines and high number of incisors. Even the fur looks opossum-like (mammal carcasses typically slough fur after they've been decomposing in water for a while, and this explains the naked face). When you add all this to the fact that the Virginia opossum is a common, widespread mammal in California we have an obvious and uncontroversial identification."
It's not surprising that people have difficulty identifying these decaying carcasses. After all, when we see raccoons and other small mammals they are typically alive, healthy, and fur-covered. Of course, people love mysteries - and as the case of the San Diego Demonoid shows - all it takes to create a mystery is someone not knowing what they're seeing. More monsters will surely wash up, and so the (temporary) mysteries will continue.