The era when life first conquered the land and oceans

Space · Published 31 October 2026 Swipe more like this →

In short: During the Devonian Period, Earth underwent a radical biological overhaul. While massive fish dominated the seas, a vascular plant explosion transformed the continents into forests, creating the first complex terrestrial ecosystems and paving the way for vertebrates to leave the water behind forever.

Spanning from 419.2 to 358.9 million years ago, the Devonian Period is famously known as the "Age of Fishes." This era saw a massive diversification of aquatic life, where new predators like sharks, bony fishes, and ammonoids began to rule the oceans. During this time, jawless fish and placoderms—including the giant 33-foot Duncleosteus—reached their peak diversity. While trilobites continued a steady decline, brachiopods emerged as the most abundant marine organisms of the Paleozoic Era.

The period was equally transformative for the terrestrial world. A spectacular "explosion" of vascular plants occurred, giving rise to major groups like lycophytes (clubmosses) and euphylophytes (ferns and seed plants). These primitive trees, such as Archeaosigillaria and Archaeopteris, fundamentally altered global carbon cycling and created extensive marshlands. This new biosphere provided the habitat for invertebrate land animals, including scorpions, spiders, and wingless insects, to begin thriving on land.

Perhaps most significantly, the Devonian served as a bridge for vertebrate evolution. Changing freshwater environments fostered the transition of fish into the first tetrapods—the lineage that would eventually become all land vertebrates. Fossil evidence from approximately 408 million to 360 million years ago reveals protoamphibians like Acanthostega and Icthyostega moving into pools alongside lungfish and placoderms. Geologically, this era also saw major tectonic shifts, including the final closure of the Iapetus Ocean and the formation of mountain chains that shaped the semi-arid continental landmasses of modern Europe.

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