Their ancestors lived in ancient shallow water. Horseshoe Crab also changed very little over the last 445 million years, is as old as Trilobites class of animals.
Some animals has been survived on the earth for millions of years, some of them may be horror, or intelligent enough to become a survivor from nature and predators.
Here is the 12 kinds of animals known as living fossils, the frilled shark, golden "Mars" ant and other ancient species animals, some of them remain almost no change over millions of years of evolution.
Perhaps these living fossils might still exist even after human extinction.