Phacopids had a late start in the Ordovician, and were wiped out by the end of the Devonian. They were extremely diversified, and we can credit them for the development of schizochroal eyes as opposed to holochroal lenses. Someone like Richard Fortey is all over the eye development of trilobites like a dirty shirt! Pictured here is the iconic Eldredgeops rana (previously Phacops rana for all the older collectors out there!). Note those distinctive eyes. We really start bumping into this new bumper crop in the Ordovician with all the Flexicalymene, Calyptaulax, and the incredible diversity of the cheirurids. By the Devonian, their diversity thinned out. There were some massive calymenids in the early Devonian, but all the cheirurids were gone after the Silurian. Eventually, it was these phacopidae and Geesopines that survived. As my dear collecting comrade says, Eldredgeops is like the cockroach of the Devonian. Their emergence in the Eifelian and Givetian was madly prolific. Proof? Now that is one gregarious assemblage!
Given their diversity, it is no wonder that almost half of my collection (roughly 60 of 150 species) is phacopids. Unlike asaphids and lichids, they never attained massive proportions. They were, however, very resilient and there is likely no continent on earth that doesn't have a few phacopids in their fossil record! Exceptions to big sizes might be Drotops from Morocco or oversized Ceraurus. The biggest authentic Drotops I've seen is about 16 cm in length -- not tiny, but not exactly a mature Uralichas either. Comments are closed.
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Kane Faucher
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February 2024
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