January 8, 2010
Every bone tells a story. It is easy to think of a bone as a static thing, a part of an animal’s body that does not change, but in truth bones are constantly being remodeled throughout the life of an organism. This was true of dinosaurs just as much as any vertebrate living today, and the fossil bones on display in museums are like snapshots into the last days of those individual animals. And, if you look closely, you might even find even more striking clues that the bones really did once belong to living creatures.
Just like flesh, bone can become infected, and such infections leave behind osteological clues that can be preserved in the fossil record. When a part of a skeleton becomes infected, the body’s immune system attacks the microorganisms in the bone, but this can have the unfortunate side effect of killing bone cells in the process. The body will then try to create new bone in those areas, but this new bone is often built up outside the surface of the original bone. This causes swellings of bone, and in 1917 the paleontologist Roy Moodie identified just such a pathology in the tail bones of a sauropod dinosaur.
Featured in his book Studies in Paleopathology, the two vertebrae came from near the end of the tail of a large sauropod dinosaur akin to Apatosaurus. Between them was a large, bulbous swelling, and Moodie thought this looked like a probable bone infection (though he was not absolutely sure). But how had the bone become infected in the first place?
Moodie hypothesized that a predatory dinosaur was to blame, but he did not envision a lively chase between predatory and prey. At the time sauropod dinosaurs were still viewed as big, stupid swamp-dwellers who were so huge that they did not even know what was happening to their own bodies half the time. Of dinosaurs such as Apatosaurus, Moodie wrote:
The tail in some of these large animals was very long and slender, and it may have been used in swimming, as a muskrat uses his today. The terminal caudals [vertebrae at the tip of the tail] in some species were reduced to mere slender rods of bone, so that a fracture or an injury of any kind in this region could easily occur. Aside from possible blows from the head, the dinosaur to which the above described vertebrae belonged was entirely defenseless. The tail, for example, might be seized by one of the carnivorous dinosaurs and vigorously chewed for some time before the owner of the tail was able to turn his huge body and knock the offender away.
For Moodie, Apatosaurus and its relatives were so dumb that they would barely even notice that they were being eaten alive, and once they did it would take a great deal of time to get its body in order to push the offending predator away. If the dinosaur who owned the tail bones Moodie described had not broken them through carelessness, then it probably had its tail chewed on for a bit by an Allosaurus or other predator.
Today, though, we know that sauropods were not so stupid as Moodie suggested. They were active creatures who trod about on dry land, and there is no evidence whatsoever that they stood by as predators nibbled their tails. Wrong as he might have been about the behavior of dinosaurs, though, Moodie was a pioneer in recognizing pathologies in fossil bones, and his work provided scientists with new insights into the lives of dinosaurs and other prehistoric animals.
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