|MadSci Network: Evolution|
The preservation of soft parts in ancient organisms is very exciting. We can see things about them that people once did not think would ever be possible. The rare preservation of soft parts in trilobites is generally limited to appendages (legs, antennae, a few other things). There are no known living trilobites, but trilobites are arthropods and they have many living relatives: insects, crabs and shrimp, spiders, and so on. All arthropods have jointed limbs that bear very small hairs. The shapes their limbs take are strongly affected by what they use them for. For example, the big claws that some crabs display are obviously for fighting, opening things that are hard to open, and activities like that. By contrast, delicate limbs that go down both sides of the body and have more or less a common shape are almost always legs used for walking. Centipedes, cockroaches, and spiders all have walking legs of this kind. Fossil trilobites that have preserved soft parts usually show the ends of legs sticking out from one or both sides of the shell (exoskeleton) and these legs look very much like the walking legs of living arthropods. That is how we interpret their function. Some fossil trilobites show very slender, long, straight appendages sticking out from under the front of the "head" (cephalon). These look like the antennae of modern arthropods and we interpret them to have been similar to modern antennae. Antennae are generally used for sensing the environment and trilobites probably used their antennae the same way. The whiskers of cats are made quite differently but they serve a similar function. Preservation of soft parts in trilobites is an excellent example of how paleontologists can compare modern organisms to ancient ones and understand something about how the ancient creatures lived. If you want to learn more about trilobites you could start by visiting the web sites of major natural history museums. Type in trilobites in the search function and you will probably find some fascinating things. David C. Kopaska-Merkel Geological Survey of Alabama box 869999 Tuscaloosa, AL 35486-6999
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