Living Fossil The earliest horseshoe crabs were found 450 million years ago as fossils in strata. Many think of them as crabs and crustaceans when in fact they are more related to spiders and scorpions. Under their enormous shell, their bodies also look more like those of spiders.
The nautilus is considered to be a living fossil. It's remained largely unchanged for the past 500 million years, since the Triassic period. The nautilus usually inhabits ocean depths of about 300m, rising to around 100m at night only for feeding, mating or laying eggs. The average lifespan of a nautilus is around 20 years.
Snapping turtles as we know them first walked the earth some 40 million years ago, but they have been virtually unchanged over the past 215 million years of their evolution, according to Tortoise Trust. Although not among the most endangered tortoises and turtles according to the Turtle Conservation Coalition, the snapping turtle is listed as threatened.
Tuataras are kind of confusing because they look like lizards, but they’re not actually lizards. They are simply (and you’ll love this) “lizard-like” members of the order Rhynchocephalia. Tuataras have many features of primitive reptiles. For example, their lungs consist of a single chamber. They also have a third, or parietal eye, which is only visible in hatchlings.