"Teaching people about the world in which we live."
"Teaching people about the world in which we live."
The chambered nautilus is called a living fossil because it has been around as an evolving species for 500 million years. This is longer than the shark’s 300 million year history. Squid and octopus share the same ancient ancestor with the nautilus. The nautilus first enjoyed a predatory advantage as a species because it was capable of changing its level in the ocean. That is, the nautilus had buoyancy. This gave it many angles of attack and much greater mobility than its prey.
Nautilus buoyancy is accomplished via its chambered shell. The nautilus shell consists of a spiral of chambers, with the nautilus animal living in the outermost chamber. The nautilus adjusts its buoyancy and hence its level in the ocean by adjusting the amount of liquid in the chambers. Thus it has its own, built-in personal flotation device. In fact, the primogenitor nautilus (the nautiloid cephalopods) became the first large, mobile predators of the sea.
The warm water temperatures near the ocean surface on the GBR are lethal to the nautilus. Nautilus stay near the ocean floor at great depths where the temperature is colder. However, the nautilus shell implodes at 2000 feet (650 meters) below the sea, so they cannot go to the greatest depths of the ocean floor. The chambers cannot be kept clear of liquid (so they can float) for very long at 1200 feet (400 meters). Hence the nautilus must live in a safe zone between the devil of warm water above and the terrible pressures of the deep blue sea below.
The need to remain in the zone makes their migrations and the colonization of species from island to island a major question since the ocean floor found between the major island chains is deeper than the critical depths. Three explanations have been offered: the larvae (which drift as plankton) colonize distant island chains, or colonization occurred during an ice age when the frozen waters of the Earth lowered the ocean levels by about 450 feet (150 meters) and made immigration easier, or some species have won a "sweepstakes colonization" prize. Sweepstakes colonization is the term evolutionary biologists use to mean a very low chance event.
The nautilus is a mysterious animal, a living fossil known since ancient human history, but only studied scientifically in its natural environment during the last century.
This summary was prepared from the book written by Peter Ward, Professor of Geology at University of Washington, Seattle.
