Paleobiology

Paleobiology is a science that draws dominantly from geology (evidence from rocks), paleontology (evidence from fossils), and biology (evidence from living organisms). The class contains both geology and biology majors, each of whom will feel disadvantaged at times as we deal with data from these different disciplines and try to meld them together.

Laboratory scientists usually try to control variables as they design and carry out experiments. For example, one might concentrate on the effect of temperature on spawning in, say, Dungeness crabs, if one was to worry about the effects of an El Nino. One could design an experiment in which crabs could be induced to spawn in lab tanks controlled at set temperatures, with everything else kept the same.

This is a valuable experiment. However, the results might not carry over into the real world, where Dungeness crabs have to worry about many other things apart from water temperature. For example, there might be fewer, or more predators in an El Nino year, and they might be different predators than those usually looking for crabs or crab eggs... and so on. It might turn out that El Nino conditions are lousy in terms of temperature for Dungeness crabs, yet other parameters balanced out the temperature effect, to leave no net result. Whatever else we are looking at as we try to survey the life of the past, we are looking at organisms that were facing real problems in the real world. We may have to abandon mindsets that are appropriate to lab science. (Ecologists face this sort of problem too.)

An example in the fossil record might be the Cretaceous-Tertiary extinction, when dinosaurs became extinct. Talk to a physicist who is modelling the impact of an asteroid, and he/she will focus on the dramatic environmental damage (dust, darkness, freezing, etc.) and likely point to asteroid impact as the cause of dinosaur extinction. Yet many creatures survived, so the solution to the question of the extinction (when we find it) is likely to have a large ecological component that can explain the differential survival. (Much more about this later in the course.)

The other major component of paleobiology is that it is a historical science. Many sciences (chemistry, physics, biochemistry, etc.) do not need to worry about history, because, they say, they deal mostly with "laws" that do not change with time. Yet the world in which those laws operate may have changed with time. The geochemist dealing with ore deposits has to remember that the Earth did not always have oxygen in its atmosphere and ocean; the astronomer studying Mars has to remember that once it had water on its surface; and a geophysicist has to remember that Earth's internal heat supply has changed over the last few billion years. The paleoclimatologist has to remember that the Earth has not always had ice caps: in fact, it "normally" does not. The geological principle of uniformitarianism ("the present is the key to the past") is a principle, not a law: it is a useful first assumption.

As historians of evolution, paleobiologists must remember that life is constantly changing. Once there was no life on land; once the only living organisms on Earth were all bacteria; once there were no swimming predators, and once there were no flying predators. In fact, once there were no predators at all.

Another disconnect can occur. Geneticists usually say that mutations occur randomly, and extrapolate that to suggest that they can study molecules that (therefore, in principle) EVOLVE at some regular rate. When they apply these principles, they reconstruct evolutionary events at times that contradict the record of evolution as displayed by fossils. Geologists therefore argue that while mutation may be random, and clock-like, EVOLUTION is not, either in principle or in practice. (Much more about this later, too.)

So what we are trying to do is to reconstruct the way that life evolved on this Earth. While there may be multiple hypotheses about any particular events or processes in Earth history, there was only one true story, and our job is to find it. (And the same applies to archeologists and historians.)

One of the delights of paleobiology (and still today, some aspects of biology) is that it is often specimen-driven. By that I mean that one lucky discovery of a new specimen can make a great difference. The discoverer has to be lucky in the sense that he or she actually SAW the specimen, BUT ALSO has to recognize the importance of the find. Here are some examples:

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Last updated August 24, 2004.

Links checked September 30, 2005.

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