King of the bugs

Trilobites are fantastically important fossils. They appear, already fairly complex animals, in the earliest Cambrian and their evolutions can be seen throughout the entire Palaeozoic era. They suffered a knock in extinction event that closed the Cambrian, and were dwindling through the Silurian and Devonian, before reaching exctinction at the end of the Permian.

So they were around for a very long time, about 300 million years, were very widespread, abundant in life and in the fossil record, and were constantly changing as they moved into a wide variety of lifestyle niches. These all help the trilobite to become a very important date marker for stratigraphy. If you find an identifiable species of trilobite, there's a good chance you'll be able to have a reasonable stab at the age of the rocks you found it in. They are also good indicators of plate tectonic movements. I studied the cladistics of a family of trilobites for my final year university project. Basically, a tool to try to establish a 'family tree'. Their migratory trends helped provide information on the closure of the Iapetus Ocean.

One of the best known trilobites is the one shown above - Elrathia kingi. It's found in such numbers and in such great condition in the Wheeler Shale deposits of Utah that it has become a fossil shop staple across the world. I buy them in Tucson, and in a couple of different sizes on matrix as well as bagged loose examples. They are carefully graded and sorted according to size - saves me a lot of trouble...

They are relatively easy to collect. The shale is quite soft and the fossils weather out of the stone. In the right places, they can often be found lying on the surface. Mostly, though, splitting the shale in a quarry will provide a decent number of good examples in a short space of time. Elrathia were used for jewellery by Native Americans living in the area, and it's easy to see why. Their size, shape and detail mean they lend themselves perfectly to this use. I've also heard they had been used as a form of currency at one point.

They're a great example of their kind, and likely the starting point for many a collection. They aren't very big, maybe up to 4cm commonly, and are so abundant as to be inexpensive. There are plenty of collectors that collect only trilobites, and I'll bet almost every one of them has an Elrathia in their collection.