Corynexochids are the second longest surviving Order of trilobites, ranging from the Cambrian to the end of the Devonian. We know this bugs mostly from their more common representatives like Illaenus or Bumastoides. One feature many of them have in common is the effaced nature of their cephalons and pygidia. These trilobites were uniquely adapted to very muddy environments, likely preferring to burrow in sediment. I've taken more of an interest in this Order in the last few years, for despite the simplicity of their body plan, they are fascinating creatures. In the Rochester shale, they can be more commonly found among bryozoan thickets, suggesting some kind of potential symbiosis or food source. Not all of them were devoid of ornamentation. If we consider the genera of Zacanthoides or Changaspis from China, we see that they were not all effaced. And then we have the Moroccan genera of Paralejurus and the scutellids like Scabriscutellum and Thysanopeltis with a distinctive rim of pygidial spikes. The scutellids and styginids are fascinating in terms of phylogeny. In entomology, we know the term "scutellum" referring to a posterior feature resembling a shield, and we see that quite distinctly in the deeply incised furrows of the pygidium of Scabriscutellum (Morocco) or Scutellum lunatus (Minnesota, USA). Another interesting feature was that they could attain to impressive sizes. If we consider Ectillaenus giganteus from Portugal or Ectillaenus benignensis from Morocco, they could reach fairly robust sizes. Canada is not as blessed with corynexochids. We can count among them Bumastoides, Bumastus, and Ekwanoscutellum, I consider myself lucky to have 15 distinct species from this interesting Order, including the handlebar mustache of trilobites, Illaenus tauricornis. Having prepared a few from Russia and partials here in North America, I have come to deepen my appreciation of this true mud bugs.
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Kane Faucher
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February 2024
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