Hundreds of millions of years later, these species are nearly indistinguishable from their prehistoric ancestors.
A horseshoe crab is seen swimming along the sea floor in coastal waters surrounding the Philippines. Horseshoe crabs are considered"living fossils", species that appear largely unchanged from their fossilized ancestors. On beaches spanning the Atlantic Coast from Maine down to the gulf of Mexico, thousands of murky brown shells carpet the sand.
Living fossils are also scarce, often the last of their kind, with no close relatives alive today, and they tend to thrive in marine environments because it is easier to sidestep extinction events deep in the ocean.This primordial, helmetlike arthropod scuttled across the sandy ocean floors from as early as the Paleozoic , sharing the seas with long gone icons of prehistory such as Trilobites, a hard shelled, insect-like creature and Orthoceras, a strange, conically shelled cephalopod.
The nautilus is a mollusk that has survived on Earth for about 500 million years, but today, they're endangered by shell collectors.Nautiluses, near mythic marine mollusks characterized by their multi-chambered shell and pinholed gaze, float through the inky twilight of the deep pelagic. “They are also superb at finding dead food," continues Ward. “These are obligate scavengers. They have no vision and stay out of the light.”
However, to the world’s surprise, the “coelacanth was dredged up in the 1930s off South Africa, and known as a fossil before it was discovered alive” says Scott Lidgard, emeritus curator of fossil invertebrates at the Field Museum. “Starting in the 1990s, molecular geneticists began examining the two species of living coelacanths, eventually finding that there are parts of the genome that appear to be rapidly evolving.
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