XENOPHANES: In order to make any sense out of dinosaurs, one needs to have at hand, and to understand, the meaning of the word "fossil" (see Oxford Dictionary definition at left). Although "fossil" is now a common and widely used word, whose meaning is known to practically everyone, the general acceptance of the idea that fossils are the remains of ancient organisms required millenia to achieve. In fact, many basic tenets in science, a heliocentric solar system (sun at the center) in astronomy for example, were established centuries before fossils were properly understood. The reasons for this are complex, but one major factor is that the great age of the earth also was not widely appreciated until relatively recently. Without an earth eons old the idea of ancient life and the idea of fossils are meaningless.

Although the true meaning of fossils is a rather recent acquisition in the history of geology, there were early glimpses of truth. Xenophanes (c.750 BC), one of the earliest known Greek natural historians appears to have been the first to recognize the true meaning of fossils. He described the occurrence of clam shells in rocks outcropping in mountainous parts of Attica. He recognized that these lithified clam shells were closely similar to clams that were then living along the coastline of the Aegean Sea. To account for the occurence of these lithified clam shells far from the present sea, he argued that they were the preserved remains of clams that had lived at an earlier time when Attica was covered by an ocean. However, in 750 BC there were no quantitative methods for verifying this idea, and so Xenophanes' rather modern-sounding explanation for these clams could not be tested, and disappeared from view. It is perhaps the earliest example of an idea ahead of its time.