Also, the first possible fossils of insects appeared around 416 Mya, in the Early Devonian. Trilobites: Though declining in numbers, trilobites continued in importance and reached their greatest size during this Period. [27], In the Early and Middle Devonian, the west coast of Laurussia was a passive margin with broad coastal waters, deep silty embayments, river deltas and estuaries, found today in Idaho and Nevada. Life was primitive during the Paleozoic and included many invertebrates (animals without backbones) and the earliest fish and amphibians. The most important group to be affected by this extinction event were the reef-builders of the great Devonian reef systems.[59]. The first ferns, horsetails, and seed plants appeared at the end of the Devonian Period. Plant Life. Brachiopods (ToL: Brachiopoda