One of the most famous of all the ancient animals were the dinosaurs—creatures that only lived on land (so far, no dinosaurs are known to have lived in the air or water)—first appearing in the early Triassic period (about 220 million years ago) and all but disappearing at the end of the Cretaceous period (about sixty-five million years ago). It is thought that modern humans (Homo sapiens sapiens) appeared only about 25,000 years ago. Although we know movies that show humans and dinosaurs existing together are only Hollywood fantasies, one caveat remains: Many scientists believe that modern birds are the ancestors of the dinosaurs—and thus, in some ways, we can say that the dinosaurs never truly became extinct! (For more about dinosaur extinctions, see the chapter “Heredity, Natural Selection, and Evolution.”)

The word “cockroach” can often send chills up a human’s spine. They are considered pests by most, but in reality, they’ve been on Earth for much longer than humans. The earliest cockroach fossils are about 350 million years old; by about 220 million years ago, cockroaches were so prolific—and are thought to have been the first organism to master flight—that many paleontologists nickname that time the “Age of Cockroaches.”

Modern cockroaches (order Blattaria or Blattodea) are nocturnal scavenging insects that eat not only human food, but book bindings, ink, paper, and seemingly everything in between. Of the about 4,500 species of cockroaches, only thirty species are associated with human habitats, and of those, only about four are considered definite pests. The most well-known one in the United States is the American cockroach (Periplaneta americana) that can measure about 1.2 inches (30 millimeters) long—although when you see them invade your kitchen at night, they seem to look much larger! The world’s heaviest cockroach is the Australian giant burrowing cockroach—a creature that can measure 3.5 inches (9 centimeters) long. They are related to the termite; in fact, recent genetic evidence suggests that termites evolved directly from true cockroaches. And they are amazing creatures that have adapted well to life on Earth; they can even go for a month without food, for two weeks without water, and the female mates once and can stay pregnant for all of her life.