The September 2006 issue of Discover magazine had an article about a scientist who practices a science called paleopathology. This is the application of the science of pathology, which attempts to understand health problems of living things, to paleontology, which is the study of fossils. Since fossils are mostly of the bones of creatures who lived so long ago their solid remains have turned into stone, studying the bones in light of our current medical understanding can reveal many things about the creatures of the past.
In the article, the scientist, Bruce Rothschild, discusses his findings about a variety of ancient and not so ancient creatures. He has challenged the idea that certain dinosaurs walked upright, because their bones do not demonstrate the types of fractures and other deformation that normally come from such a posture. He has also bolstered the theory that dinosaurs like the Tyrannosaurus rex did walk upright. Other findings suggest that T-rexes may have ad rough sex.
Another finding relates to creatures that dive deep underwater to catch prey. Diving too deep for too long and rising too quickly can lead to a condition called the bends, in which bubbles of gas form in the bloodstream which can cause damage to the brain and joints. But Rothschild has found evidence of the bends in the bones of certain diving creatures of the past. This suggests that some creatures evolved a way to cope with this condition and survive where others would be killed or crippled. He hopes this may lead to ways of allowing humans who dive deep to cope with the same problem.
Critics of biological evolution try to cast doubt upon the value of fossils in proving evolution. In fact, fossils are a very rich window on the past, allowing us to understand many intricate details of life forms that are no longer around. The changes in bone structure over time gives enough evidence of evolution to establish the theory, even if there were no other evidence for the theory (which there is). This shows the lie that we cannot test the theory of evolution because we cannot test theories with experiments.
Just as the forensic scientists who investigate crimes can testify to events of the past based on evidence found in the present, so can paleontologists describe the creatures of the past based on the evidence they have left for us to find millions and even billions of years later.