Palaeontology and Phylogeny

Abstract

Millions of years before arthropods had succeeded in colonizing the land, the primaeval oceans were teeming with them. They, in turn, had probably evolved from segmented, worm-like ancestors, similar to today’s polychaete annelids; but fossil evidence of this is lacking. Trilobites and Crustacea are known from the Cambrian period, Eurypterida from the Ordovician, Diplopoda from the Devonian or possibly earlier, Collembola and probably Insecta also from the Devonian. Myriapods, Collembola, and Insecta are probably descended from an onychophoran-like ancestor. The mid-Cambrian Aysheaia pedunculata (found in British Columbia in a marine deposit, along with polychaetes, trilobites, holothurians etc.) may have been such an animal, but other interpretations of it have also been made.