The Age of Fishes
Devonian
Paleozoic Era · 419.2 – 358.9 million years ago
The Devonian Period lasted from about 419.2 to 358.9 million years ago, roughly 60 million years. Often called the Age of Fishes, it saw fish diversify spectacularly, the first forests spread across the continents and the first four-limbed vertebrates appear.
It was a world of armoured fish the size of cars, vast tropical reefs and landscapes that turned green for the first time. Yet the Devonian also ended in one of the Big Five mass extinctions, which devastated reefs and many groups of fish.
Key facts
- Began
- 419.2 MaMillion years ago
- Ended
- 358.9 MaMillion years ago
- Duration
- 60.3 million years
- Era
- Paleozoic“Ancient life”
- Global temperature
- ~21°CRoughly 19–22°C · today 14.5°C
- Plants on land
- Forests
- Atmospheric CO₂
- Falling, from several thousand ppm to perhaps ~1,000
- Oxygen
- Rising, possibly near modern levels by the end
- Sea level
- High, with extensive warm shallow seas
- Continents
- Laurussia near the equator; Gondwana to the south
- Signature life
- Dunkleosteus, Tiktaalik, Archaeopteris, ammonoids
- Began with
- Small plants and fish diversifying after the Silurian
- Ended with
- Late Devonian extinctions (Kellwasser and Hangenberg)
Ages follow the International Chronostratigraphic Chart (ICS). Global temperatures are rough reconstructions after Scotese et al. (2021); ancient CO₂, oxygen and sea-level values carry large uncertainties.
Epochs of the Devonian
- Early Devonian419.2 Ma – 393.3 Ma
- Middle Devonian393.3 Ma – 382.7 Ma
- Late Devonian382.7 Ma – 358.9 Ma
Continents and oceans
Laurussia, formed by the Silurian collision of Laurentia, Baltica and Avalonia, lay across the equator. Erosion of its Caledonian mountains filled surrounding basins with red river sediments, the Old Red Sandstone, which is why geologists sometimes call it the Old Red Continent.
Gondwana occupied much of the southern hemisphere and was moving north, gradually narrowing the Rheic Ocean between it and Laurussia. Their approach brought mountain building along the eastern edge of North America, the Acadian orogeny, and foreshadowed the later assembly of Pangaea.
Siberia and several smaller blocks lay further north, and the vast Panthalassic Ocean covered most of the globe. High sea levels flooded continental margins, creating broad tropical shelves ideal for reefs.
Climate and atmosphere
The Early and Middle Devonian were mostly warm greenhouse times. As deep-rooted plants and forests spread, they broke down rock and built soils, which many scientists think accelerated chemical weathering and drew carbon dioxide out of the atmosphere.
By the Late Devonian the climate was cooling, and by the very end of the period glaciers had formed in parts of Gondwana, in what is now South America. Oxygen levels appear to have risen through the period, helped by expanding plant life, although exact values remain uncertain.
Life in the Devonian
Life in the Devonian changed on land and in water at once. Fish reached a peak of diversity, plants grew from ankle height into trees, and some lobe-finned fish began the transition to life on land.
The Age of Fishes
Armoured placoderms dominated, among them Dunkleosteus, a predator perhaps around 4 metres long with self-sharpening bony jaw plates. Early sharks such as Cladoselache, spiny acanthodians and ray-finned and lobe-finned fish shared the seas.
Reefs and ammonoids
Some of the largest reef systems in Earth's history grew in Devonian seas, built by stromatoporoid sponges and corals. Coiled ammonoids appeared early in the period and became important swimming predators.
The first forests
By the Middle Devonian, tree-like plants such as Wattieza formed the first forests. In the Late Devonian, Archaeopteris, with true wood and leafy branches, grew into large trees, and the first seed plants appeared near the end of the period.
Fish with legs
Lobe-finned fish gave rise to the first tetrapods. Tiktaalik, from about 375 million years ago, combined gills and scales with a neck and sturdy fins, while Acanthostega and Ichthyostega had true limbs with digits.
Timeline of key events
- 419.2 Ma
Devonian begins
The period starts at Klonk in the Czech Republic, defined by the graptolite Monograptus uniformis.
- 407 Ma
Rhynie chert ecosystem
Hot springs in Scotland entomb early plants, fungi and arthropods in silica, preserving them cell by cell.
- 390 Ma
Earliest forests grow
Tree-like plants form the first forests, with fossil stumps known from New York State.
- 375 Ma
Tiktaalik
A fish with a neck and sturdy limb-like fins lives in shallow streams of what is now Arctic Canada.
- 372 Ma
Kellwasser extinction
Ocean anoxia and climate disruption at the Frasnian–Famennian boundary devastate reef ecosystems.
- 365 Ma
Tetrapods with digits
Acanthostega and Ichthyostega, with true limbs and digits, live in the swamps of what is now Greenland.
- 358.9 Ma
Hangenberg event
A final extinction pulse, linked to glaciation and anoxia, ends the placoderms and closes the period.
How the Devonian ended
The Late Devonian mass extinction was not a single event but a series of crises. The largest, the Kellwasser event around 372 million years ago, struck at the Frasnian–Famennian boundary and caused the collapse of the great reef ecosystems. The Hangenberg event at the very end of the period, around 359 million years ago, hit ammonoids and vertebrates hard and wiped out the placoderms.
Together these events removed an estimated 70% or more of marine species. Proposed causes include widespread loss of oxygen in the oceans, climate cooling and glaciation, nutrient runoff linked to the spread of land plants, and volcanism, but scientists still debate their relative importance.
Where to see Devonian fossils
The Rhynie chert in Aberdeenshire, Scotland, preserves early plants, fungi and arthropods in microscopic detail. Miguasha National Park in Quebec, a UNESCO World Heritage Site, is famous for fish such as Eusthenopteron, and the Gogo Formation of Western Australia yields three-dimensional fish with soft tissues.
Tiktaalik was found on Ellesmere Island in Arctic Canada, and Acanthostega and Ichthyostega in East Greenland. The Cleveland Shale of Ohio produced Dunkleosteus, the Hunsrück Slate of Germany preserves delicate starfish and arthropods, and Gilboa in New York State is known for its fossil tree stumps.
Surprising facts about the Devonian
- A Devonian year had about 400 days. Daily growth lines in fossil corals reveal that Earth spun faster then, so each day lasted only around 22 hours.
- Prototaxites, a trunk-like organism up to about 8 metres tall, towered over Early Devonian landscapes. It is widely thought to have been a giant fungus, though its exact identity is still debated.
- Fossil trackways from Zachełmie in Poland, about 395 million years old, suggest that four-limbed animals existed millions of years before Tiktaalik, a puzzle palaeontologists are still working through.
- A placoderm fish from the Gogo Formation in Australia, Materpiscis, was found with an embryo still attached by an umbilical cord, the oldest known evidence of live birth in vertebrates.
- The Devonian is the only geological period named after an English county: Devon, where Adam Sedgwick and Roderick Murchison studied its rocks in the 1830s.
- The earliest tetrapods had more than five digits: Acanthostega had eight fingers on each hand and Ichthyostega seven toes on each foot.
Where it sits in deep time
The globe beside this article shows Earth 385 million years ago, reconstructed from the PALEOMAP paleo-elevation models. Step to another period and watch the continents drift into place.