Chapter Eleven

1. Chapter Eleven The Record of the Past

2. Fossils and Their Interpretation • A fossil is the remains or traces of an ancient organism. Several conditions must be met for fossilization to occur. • The fossil record is not a complete record of the history of living organisms on the face of the earth. It exhibits sampling error. • Fossils can give us information about the size, shape, and function of different muscles, the relative importance of the senses, and approximate brain size. Additionally, information about disease, injury, growth, and development may be found. • Artifacts are important clues to hominid behavior.

3. Fossils Fossilized bone(limb bones of Baluchterium) Cast(Archeopteryx) Tracks (dinosaur) Image #315485 American Museum of Natural History Image #325097 American Museum of Natural History Image #125158 American Museum of Natural History

4. Taxonomy and the Fossil Record • The definition of a species in living animals is based on reproductive success, a concept which would be difficult to apply to the fossil record. • The typological viewpoint is that basic variation of type is illusory and that only fixed types are real. Typologists are more likely to split two specimens that differ into two separate species. • The populationist viewpoint is that only individuals have reality and that type is illusory. Variation underlies all existence. Populationists would be more likely to lump two specimens that differ into a single species. • A paleospecies is defined in terms of morphology rather than reproductive success. A chronospecies is an arbitrarily defined division in an evolutionary line based on time. • Age, sex, and genetic differences all lead to variability in the fossil record.

5. Geological Time • Relative dating provides information on which fossils in a sequence are older or younger. Stratigraphy is based on the principle of superposition, which states that the lower strata are older than those above. • Methods like flourine dating can help establish if two bones are contemporary. • Certain fossils or combinations of fossils are commonly found and have become markers for particular periods of time. These are known as index fossils.

6. Radiometric Dating Techniques • Radiometric dating methods are based on the decay of radioactive materials. Radioactivity means that the atom is unstable and will decay into another type of atom. • If we have a given number of atoms, we can say that one-half will have decayed in a specific number of years known as the half-life. • Dating techniques include fission-track, thermolumine-scense dating, electron spin resonance dating, amino acid racemization, and the geomagnetic time scale.

7. Radiometric Dating • Potassium-Argon dating is based on the radioactive decay of potassium 40, which has a half-life of 1250 million years. • Radiocarbon dating is based on the decay of carbon 14, which has a half-life of 5,730 years.

8. The Geological Time Scale • The evolution of life has been greatly affected by earth dynamics. Shifting landmasses create new migratory routes and destroy others. Plate tectonics also are responsible for many alterations in climate. • Geologists have divided the history of the earth into a hierarchy of units: era, period, and epoch. • The three large eras are the Paleozoic, the Mesozoic, and the Cenozoic.

9. The Cenozoic • The Cenozoic is known as the Age of Mammals, as it is the time of the adaptive radiation of the mammals. (Source: W.B. Harland et al. A Geologic Time Scale 1989 (Cambridge: Cambridge University Press, 1990).