The true arthropods – or euarthropods – make up the majority of panarthropods, and include the modern chelicerates (sea spiders, horseshoe crabs, and arachnids), the myriapods (millipedes and centipedes), and the pancrustaceans (crustaceans and insects), along with various completely extinct groups like the trilobites.
The earliest fossil evidence associated with some sort of euarthropod presence are trace fossils dating to only a few million years after the start of the Cambrian (~537 million years ago), and the group’s common ancestor is estimated to have split off from the radiodont lineage no more than 550 million years ago in the end of the Ediacaran.
…And this is where things get more complicated.
Continue reading “Cambrian Explosion #45: Stem-Euarthropoda”