The trilobite — an extinct marine creature with numerous legs and a uniquely shaped exoskeleton — occupied almost every ecological niche available to its phylum throughout the Palaeozoic era. In a talk in the 'Café Scientifique' series at London's Dana Centre, the creatures were introduced as “eyewitnesses of evolution” by Richard Fortey, a Merit Researcher at the London Natural History Museum (http://www.danacentre.org.uk/events/2009/02/18/488).

Fortey's affection for the organisms that have been the focus of his scientific career was apparent throughout the highly engaging talk. A highlight focused on the development of the trilobite eye — one of the most complex ever captured in the fossil record. Trilobite eyes were made of a staggering number of tiny calcite lenses, ranging from the hundreds to thousands, some of which Fortey himself counted in his days as a post-graduate student.

Some of the uniquely adapted eyes could see 360°, and one of Fortey's favourite eyes had a special 'shade' that served as a sun visor, allowing the creature to see prey at distance across the sea floor. Other trilobites had variable amounts of magnesium within the crystal structure of the lens, apparently for the purpose of focusing the lens.

Images from the expansive trilobite fossil record captured the audience's imagination, from smooth little burrowers occasionally found in North American backyards to elaborately spiked, spined and even trident-bearing versions unearthed from the sands of North Africa. The creatures described ranged from humble pillbug-like creatures burrowing across the sea floor to metre-long, armoured predators that terrorized the water column.

Both the lecture and the subsequent discussion ended on the trilobite fossil trade. Like dinosaur fossils in China, trilobites from North Africa have become a commodity — several specimens on sale at London's luxury department store Harrods turned out to be unknown species. However, Fortey pointed out a potential upside: he and his colleagues were not able to find representatives of all these new species on subsequent field trips; without a market for the fossils, these species may never have been found.