Walking with Trilobites by Roy McGurn

The October talk was by member Roy McGurn.
Summary by Roy

The talk was inspired by a field trip led by Tony Crimes, a leading trilobite expert in 1970 to the Nant Ffrancon valley. In particular Tony was a leading specialist in trilobite tracks, commonly attributed the ichno-genus Cruziana, amongst others.

Cruziana,Vale do Pônsul, Penha Garcia, Portugal by Correia PM Wiki Commons

Until this time trace fossils had been more of a curiosity, as mainstream fossils were more useful for dating, still very much an objective in geological research. Trace fossils are usually found quite separate to body fossils, so correlating the two is difficult, as different modes of preservation are at play.
A trace fossil may have more than one causal animal, Cruziana has been identified in the Triassic, long after trilobites became extinct. One animal may also be responsible for several trace fossils, depending on it's behaviour.
What trace fossils tell us is how the animal behaved, culminating in the stunning walking with dinosaurs films. In this instance Tony was able to say what a trilobite was doing - resting, starting or finishing swimming or feeding and burrowing. How they moved and the prevalence of juveniles etc in the population. It is assumed, for example, that juveniles were pelagic. 
That year Tony had chaired an international conference on trace fossils with a Prof Seilacher of Tubingen under the auspices of the Liverpool Geological Society. Together with Richard Fortey possibly the modern triumvirate of trilobite men.
The main sites are 2000 ft up the sides of Cwm Cuenant, a daunting field trip today probably classifying as a rock climbers "scramble" or worse. However a "debris" field behind a cottage, Ty Newydd, can be quite productive of actual fossils.

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