Chitin is a biological material found in the cuttlebones, or internal shells, of cuttlefish. It has a maximum shelf life of thousands of years, and yet researchers recently verified—using three separate techniques, multiple laboratories, and careful material handling—that samples of chitin from fossils had the same basic chemistry as modern chitin.

Cuttlefish are mollusks that look somewhat like squid. They have an internal, hard, supportive structure with soft organs around and inside it. This resilient "cuttlebone" is made of cleverly woven strands of a biochemical material called chitin and mixed with a hard biomineral called aragonite.

Many believe that fossils represent organisms that died millions of years ago. Scientific literature, however, contains dozens of well-described original soft tissues in fossils. Since laboratory tests have shown that organic tissues decay in only thousands of years, these fossils have been at the center of much heated controversy.

Cambrian rock layers contain many strange animal fossils, and very few fossils appear in layers below them. Called the "Cambrian explosion of life," the creatures in these layers come from all the major groups of animals alive today (including fish, which represent the vertebrates), plus many more that later became extinct.