evidence: The fossil record is filled with strange marine animals that would look like sea monsters if they were alive today. From the creepiest Cambrian critters to massive marine reptiles, wonderfully weird sea creatures have inhabited our oceans for over half a billion years. We've put together a list of 25 of the strangest ancient sea monsters ever to have lived, all of which went extinct long before humans came along. [...] Saccorhytus coronarius was essentially a wrinkly sac with no anus. These weirdos lived during the Cambrian period around 500 million years ago and are known from microfossils discovered in China. The Minion-like creatures may have spent their days catching prey in seafloor sediment, but researchers' understanding of the animals' lives is limited. They are believed to be related to penis worms and mud dragons.