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.
The only reason we know that these evolutionary marvels existed is because some left behind fossilized remains in rocks. Modern researchers are still interpreting these fossils and making fresh discoveries all the time, so be sure to keep up with the latest Live Science fossil news.
