The very best science book for laymen is the book that is written by an expert in a field about his favorite area of expertise. So it is a delight to read _Trilobite! Eyewitness to Evolution_ (Knopf) by Richard Fortey. Fortey is surely an expert; he is a senior paleontologist at the Natural History Museum in London, and has done extensive research in fossil fields all over the globe. His favorite specimens (he refers to them as "my animals") are trilobites, and reading his lucid, humorous, enthusiastic pages, one can certainly understand why.
Fortey writes with humor about his adventures in the field. He has hunted trilobites everywhere on the globe, in desert as well as arctic wastes. But of course, most of Fortey's book is about the trilobite itself. The name comes from it's three lobes, not head, thorax, and tail, but the central body axis flanked by the left and right pleural regions. It was originally thought to be some sort of flatfish, but as more specimens were found, it became clear that it was an arthropod, with the nearest living relative the horseshoe crab (although they look more like the woodlice or roly-poly bugs, and some balled up like them). What is generally fossilized in trilobites is the outer upper shell. The underside, with the legs, is thin cuticle that decomposed before fossilization could take place. It was only when specimens were found from a certain field in New York state that details of limbs became plain. Because of a peculiarity in the minerals of the area, the thin cuticle had become gilded with pyrites, fool's gold. Every segment was shown to have a pair of branched legs, and the creature even showed antennae. Fortey's chapter on trilobite eyes, the only ones ever to use calcite prisms for lenses, is amazing.
In Fortey's account, trilobites become interesting in themselves, but he clearly shows that they have larger importance. Trilobites were always marine, never freshwater, and they generally inhabited the coastal areas. Because of this, the outline of trilobites in what is now land shows where the coasts used to be. Trilobites help to track the movements of the continents as they split off and sailed to their current positions on the globe over millions of years. Fortey shows how tracking trilobites can sometimes top paleomagnetism as a way of documenting continental drift. In addition, trilobites serve as timekeepers. They are found all over the world and range through such times as Cambrian, Devonian, and Permian, and if you can confidently identify a trilobite, you can spot what range of times your rocks come from.
Trilobites lived for over three hundred million years (humans have been around about a thousandth of that time), so they had, as the British say, a very good innings. They have been gone for over two hundred and fifty million years, and yet in this fascinating book, they live still and, with help from a superb reporter, they have news to tell us.