Trilobite

Bruce Ediger

Trilobite: Eyewitness to Evolution

Richard Fortey, 2001, ISBN 978-0375706219

Trilobite book cover

The cover is a bit weird, as it feature euryptids and horseshoe crabs as well as trilobites. Horseshoe crabs are mentioned in the book, Fortey believed in 2001 they were close relatives of trilobites, but euryptids never come up.

The story in the book actually merits the “Eyewitness to evolution” subtitle.

  • Trilobite eyes are unique among arthropods. Fortey includes a chapter on them, complete with crystallography of the calcite that trilobites used as lenses.
  • Trilobite fossils are used in biostratigraphy, to correlate layers of sediment separated by horizontal distance, providing a witness to continental drift. -Trilobite fossils were used to validate “punctuated equilibrium” models of evolution, and to demonstrate heterochrony
  • And trilobites underwent evolution as all families of animals do.

This book is a decent popular introduction to trilobite paleontology. Like all popular paleontology books there’s lots of the human history, from the first time some European notes a trilobite fossil in print (as “flat fish”, 1688, England, Reverend Edward Lhwyd), and trilobites appearance in the fiction of Thomas Hardy.

There’s the usual brief graphic rundown of the anatomy of the subject:

diagram of trilobite anatomy

There’s some evolutionary biology. Fortey discusses how an unbroken series of sediment layers containing various trilobite species contains an illustration of punctuated equilibrium.

Trilobite fossils are used in paleogeography. Paleomagnetism can give a rough idea of a paleocontinent’s rotational orientation on the globe. Fortey describes how trilobites can be used to place paleocontinents’ latitudes. The only thing about this I found troubling is distinguishing arctic from temperate from tropical trilobites. The last one died in the end Permian mass extinction, 252 million years ago. Nevertheless, this is a far better explanation of how those “here’s the Earth in the Ordovician Period!” maps get made.

Reasonable guess at an Ordovician globe projection

Fortey writes a little about using cardboard cutouts of ancient continents to get plausible arrangements.

There’s even a bit of taphonomy in the discussion of how people figured out what trilobite legs looked like.

This is well written, Fortey can actually turn a phrase, he’s a little more florid than Michael J. Benton was in When Life Almost Died

All in all, an enjoyable, informative read.