Frilled Shark: Deep-Sea "Living Fossil"

Dwelling in deep waters, the Frilled Shark features fringed gills, earning its name. It's often referred to as a "living fossil" due to its primitive appearance. It has the longest gestation period of any vertebrate, at up to 3 1/2 years. It is seldom observed because of its life so close to the bottom of the ocean until they rise to the surface before their deaths, a lifestyle that has caused the species to remain relatively the same for thousands of years.