The euthycarcinoids were a group of euarthropods known from the mid-Cambrian to the mid-Triassic (~500-254 million years ago), surviving through multiple mass extinctions including the devastating “Great Dying” at the end of the Permian that finished off the trilobites. But despite an evolutionary history spanning around 250 million years they have a very sparse fossil record, extremely rare and known from less than 20 species across their entire time range.
For a long time their affinities were uncertain, and they’ve been variously suggested to have been crustaceans, trilobites, or chelicerates, or even to have been a lineage of earlier stem-euarthropods. But since the early 2010s better understanding of their anatomy has placed them in the mandibulates, probably as the closest relatives of the myriapods and helping to close the gap between the aquatic ancestors of that group and their earliest known terrestrial forms.
Continue reading “Cambrian Explosion #56: Euthycarcinoidea”