FIGURE 2.1 Hominid footprints overprinting other hominid footprints, suggesting that one hominid purposefully stepped into the footprints of another preceding it. Cast of original trackways, which were preserved in 3.5 million-year-old volcanic ash in Laetoli, Tanzania.

remains. But the controversy was mostly put to rest when paleoanthropologists found footprints attributed to these same hominids in a 3.5 million-year-old deposit. The tracks not only showed upright walking, but an ease with it, as one individual had purposefully stepped in the tracks of a preceding one (Fig. 2.1). Moreover, a nearby smaller individual, possibly a juvenile, also showed the same evidence of bipedal-ism, meaning that three individuals were all walking in the same way. In this case, and in many others, body fossils and trace fossils certainly constitute different forms of fossil evidence, with one not being necessarily better than the other. The scientific significance of the evidence depends on the factually-based quality of the fossils themselves and how carefully the associated observations are recorded and interpreted.

Facts are described through collecting data ("data" being the plural form of "datum"), which comprise the recording of observations. Not all data are created equally, however, and the quality of the descriptive methods and the classification of data are important for distinguishing what is useful for science and what is not. For example, a dinosaur bone might be seen protruding from the ground by two different observers, who respectively record their data as follows:

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