Review: Trilobite! Eyewitness to Evolution

Perhaps the title "Trilobite!" does not have quite the threatening ring of "Jaws!" or "Carnosaur!" (with or without the exclamation point), but the sub-title really gets to the meat of the book. The trilobites were eyewitnesses to evolution in many different ways. Richard Fortey, trilobite specialist at the Natural History Museum in London and a fine writer, is an ideal guide, not just for his expertise in the animals, but for his literate approach to the history of knowledge about trilobites and for his ability to use them to show how scientists approach evolutionary problems with fossils.

Fortey is the author of several excellent books, including Life, Fossils, the Key to the Past, and The Hidden Landscape. Far more than a taxonomic specialist, he has spent his career studying the importance of trilobites to major problems in evolution, including their relationships, their geographic spread and what this might say about correlating rocks from ancient ocean bottoms, and their morphological diversity and functions. Given the scope of his other books, it is not surprising that Fortey chose to introduce readers to his beloved fossils using a problem-centered approach (rather than a dry, taxonomic, textbook-like one). An especially pleasant added value is his penchant for literature, local history, and the development of the field with all its personalities, which allows the reader a vivid and close look at the science.

"Eyewitness" is an especially apt theme for the book. Fortey begins by taking us to a spot on the North Cornwall coast called Beeny Cliff. This is where Thomas Hardy famously situated a scene in his early novel A Pair of Blue Eyes that became the archetypal — and literal — cliff-hanger of Victorian prose. In the novel, Knight, one of the protagonists, slips and tumbles over the edge of the cliff. Clinging to his life, desperately waiting for aid, Knight comes face to face with a trilobite embedded in the rock, which stares at him with stony eyes dead for millions of years. Instead of seeing his life flashing before him, Knight, an amateur scientist, sees the history of life — from primordial slime to iguanodons and mammoths. It has been known for some years that Hardy cribbed the paleontological knowledge in this passage from one of Gideon Mantell's popular books of the time. Fortey reveals another twist to the cliff-hanger: there are no trilobites in that particular geologic section.

But the eyes of the trilobite that stared at Hardy's Knight are amazingly complex and varied structures, originally formed of calcite. Trilobites retained this ocular legacy through their evolutionary history, but found ways to modify the crystal structure and the number and size of the lenses. Recent technology has enabled scientists to model and simulate the structure of these eyes in order to understand just what trilobites saw and how the eyes evolved. They certainly witnessed a great deal of geologic history.

Trilobites are distributed all over the world, from the Cambrian to nearly the end of the Permian, roughly speaking the first 300 million years of the good fossil record that we call the Paleozoic Era. From their earliest appearance they are quite diverse, and they are notorious for their rapid rates of origination and extinction of species. This is borne out by Fortey's remark that even in the Early Cambrian, trilobite faunas are different from one another in different parts of the globe. As continental shelves separated and collided and moved all over the world, the trilobites kept pace. Like few other groups, they point geologists to rock strata that have similar faunas that reflect deposition at about the same time. This has helped tremendously in correlating and connecting ancient pieces of real estate into a cohesive history of geologic strata.

Fortey's book also covers the people who have been witness to the developing understanding of trilobites, which were first interpreted as odd flatfishes. He paints fine portraits of geologists and paleontologists who have braved rain, cold, and provincial cooking to search out these petrified beasts in the remotest places. Fortey recounts how knowledge of the trilobites expanded through time as better-preserved specimens revealed a fantastic diversity of eyes, legs, segments, and spines. And he explains how recent advances in developmental biology have revealed the probability that Hox genes underlay these variations, just as they do in living arthropods. One of Fortey's most interesting portraits, to me, was his account of the Cambrian "explosion" of trilobites and other invertebrates. Fortey cuts through a lot of the silliness about "phyla" and timing of diversification that seems to flummox creationists like Jonathan Wells and Phillip Johnson — neither of whom is conversant with the evidence.

Readers should not expect to find an omnibus reference book on trilobites. Fortey has a lot to teach about trilobite structure, diversity, and evolution, but his book is far less pedestrian and far more engaging than a more text-like treatment would have been. Rather, he has used trilobites as a vehicle to explain a great many aspects of evolution, geologic history, and how we know what we know about these ancient animals and the problems that they illuminate. Besides, his prose is genial and knowledgeable and his diction is superb. We in the field of evolution are lucky to have a great many fine writers, and Richard Fortey is one of the best.

A word of caution: Trilobites are among the most popular and available invertebrate fossils — in particularly a number of species from Morocco, some of which Fortey figures in his book with elaborate spines, horns, tails, and legs. But caveat emptor: commercial purveyors often "restore" the finer and more lucrative details, and your local fossil emporium might not know this (or tell you).

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