Key Takeaway: The Devonian Period lasted about 420 to 359 million years ago. Fishes diversified dramatically, extensive reefs flourished, the first forests transformed the continents, and vertebrates began the transition onto land. The period ended after a prolonged series of environmental crises and extinctions.
Fast Facts about the Devonian Period
Time Range: About 419.62 to 358.86 million years ago. The Devonian lasted nearly 61 million years and was the fourth period of the Paleozoic Era.
Era: Paleozoic Era, the interval when marine ecosystems diversified and increasingly complex life became established on land.
Period Before: Silurian Period. The Silurian saw the recovery of marine ecosystems, the spread of reefs, increasingly diverse jawed fishes, and the earliest recognizable vascular-plant communities.
Period After: Carboniferous Period. Vast coal-forming wetlands, diverse amphibians, giant arthropods, and the earliest amniotes became important during the Carboniferous.
Named By: Adam Sedgwick and Roderick Impey Murchison in 1839. They named the system after Devon in southwestern England, where its rocks were studied.
Best Known For: The Age of Fishes, large reef systems, the first forests, the diversification of land plants and arthropods, the fish-to-tetrapod transition, and the Late Devonian biodiversity crisis.
Famous Life: Placoderms such as Dunkleosteus, early sharks, ray-finned fishes, lobe-finned fishes, lungfishes, ammonoids, brachiopods, corals, stromatoporoids, crinoids, trilobites, early trees such as Archaeopteris, and early tetrapods such as Acanthostega and Ichthyostega.
Famous Fossil Sites: The Gogo Formation of Australia; the Rhynie Chert and Old Red Sandstone of Scotland; Miguasha in Quebec; the Hunsruck Slate of Germany; the Cleveland Shale and Silica Formation of Ohio; the Hamilton Group of New York; Red Hill in Pennsylvania; and the Anti-Atlas of Morocco.
Where the Devonian Period Fits in Geologic Time
The Devonian Period was the fourth period of the Paleozoic Era. It followed the Silurian Period and came before the Carboniferous. The current International Chronostratigraphic Chart places it from about 419.62 to 358.86 million years ago.
The Devonian is divided into three series or epochs. The Lower Devonian contains the Lochkovian, Pragian, and Emsian stages. The Middle Devonian contains the Eifelian and Givetian stages. The Upper Devonian contains the Frasnian and Famennian stages.
The Devonian was long enough to include several major ecological transformations. Jawed fishes expanded into marine and freshwater habitats, reef systems reached enormous scales, forests spread across floodplains, and vertebrates developed limbs and other adaptations associated with shallow-water and terrestrial movement. The transition into the Carboniferous followed the Hangenberg crisis near the end of the period.
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History of Discovery and Naming: Sedgwick, Murchison, and the Devonian System
The Devonian was formally established during a difficult nineteenth-century debate over the age of rocks in Devon and Cornwall. These thick sequences contained slates, limestones, volcanic rocks, and the strongly altered remains of marine animals. Their position was confusing because the fossils and rock types did not fit neatly into the systems already recognized elsewhere in Britain.
Adam Sedgwick and Roderick Impey Murchison worked together in southwestern England and concluded that the disputed rocks formed a distinct interval between the older Silurian and younger Carboniferous systems. Fossil specialist William Lonsdale provided crucial evidence by showing that corals from the South Devon limestones appeared intermediate between Silurian and Carboniferous forms.
Sedgwick and Murchison introduced the Devonian System in 1839, naming it after the county of Devon. The new system helped resolve the controversy and demonstrated the growing importance of fossils for correlating rocks that had been folded, faulted, metamorphosed, or separated by great distances.
William Daniel Conybeare was not one of the two geologists who named the Devonian, but his earlier work with William Phillips helped establish the stratigraphic framework of England, including the younger Carboniferous rocks above the disputed interval. The Devonian therefore emerged from a broader generation of geological mapping and fossil comparison that transformed the Paleozoic time scale.
What Earth Was Like During the Devonian Period
During the Devonian, Laurentia, Baltica, and Avalonia were joined into the large equatorial continent commonly called Laurussia or Euramerica. Gondwana remained enormous and occupied much of the Southern Hemisphere, while Siberia and several smaller continental blocks lay elsewhere around the globe.
Continental collisions continued to close ancient oceans and raise mountain belts. In eastern North America, the Acadian Orogeny produced mountains whose erosion supplied vast quantities of sediment to nearby basins. These sediments helped build the Catskill Delta complex, preserving freshwater fishes, plants, forests, and early tetrapods.
Broad tropical seas covered parts of the continents. Warm, shallow water supported enormous reef complexes built mainly by stromatoporoid sponges, tabulate corals, rugose corals, algae, and microbial communities. Muddy offshore shelves supported brachiopods, bryozoans, crinoids, mollusks, trilobites, and diverse fishes.
Much of the Devonian had a greenhouse climate, but conditions changed substantially through the period. The spread of deep-rooted plants accelerated chemical weathering and changed soils, rivers, nutrient transport, atmospheric carbon dioxide, and the global carbon cycle. Later Devonian intervals included cooling, sea-level fluctuations, and the repeated expansion of oxygen-poor water in marine basins.
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Life and Major Evolutionary and Environmental Events
The Devonian is one of the most transformative intervals in the history of life. Marine ecosystems included giant reef complexes and increasingly complex food webs, while fishes diversified into many major lineages. On land, low vegetation gave way to the first forests, soils deepened, arthropod communities expanded, and vertebrates began evolving the anatomy of tetrapods.
The Age of Fishes
The Devonian is often called the Age of Fishes because jawed vertebrates underwent a major evolutionary radiation. Placoderms, an extinct group of armored jawed fishes, ranged from small bottom dwellers to large open-water predators.
Dunkleosteus: Armored Predator of the Late Devonian
Dunkleosteus was a large arthrodire placoderm that lived during the Late Devonian. Its head and the front of its body were protected by thick, interlocking armor plates. Instead of conventional teeth, the front edges of its bony jaw plates formed sharp cutting surfaces that could shear through prey.
Most Dunkleosteus fossils consist of skull and shoulder armor, while the unarmored rear portion of the body is rarely preserved. Its exact length and body proportions therefore remain debated, but fossils from the Cleveland Shale of Ohio show that it was one of the largest predators in its ecosystem. Learn more about its fossils, anatomy, size estimates, and feeding adaptations in the Fossilguy Dunkleosteus guide.
Early cartilaginous fishes also diversified. These shark relatives were generally smaller and anatomically different from most modern sharks, but they already displayed a variety of spines, teeth, fins, and feeding adaptations. Fossil teeth, fin spines, scales, and occasional articulated skeletons document their increasing importance.
Bony fishes split into two great branches: ray-finned fishes and lobe-finned fishes. Ray-finned fishes remained relatively modest in diversity but would later become the dominant vertebrates of aquatic ecosystems. Lobe-finned fishes included coelacanth relatives, lungfishes, and the lineage that ultimately produced tetrapods.
Devonian fishes occupied coral reefs, open seas, estuaries, lakes, rivers, and floodplains. Some crushed shelled prey, some filtered or gathered small food items, and others hunted fishes and invertebrates. The expansion of fishes reshaped aquatic food webs and established many of the broad vertebrate lineages that survive today.
Devonian Reefs and Marine Ecosystems
Devonian reef systems were among the largest and most extensive of the Paleozoic Era. Stromatoporoid sponges formed thick, layered skeletons that helped bind and strengthen reefs. Tabulate and rugose corals added branching, honeycomb, chain-like, and horn-shaped colonies, while algae and microbial crusts filled and stabilized spaces between larger organisms.
These reefs supported rich communities of brachiopods, crinoids, bryozoans, gastropods, bivalves, cephalopods, ostracods, trilobites, and fishes. Nearby muddy seafloors could be equally diverse, with filter-feeding brachiopods and bryozoans forming dense shell beds and crinoid stems accumulating in large numbers.
The earliest true ammonoids appeared during the Devonian and rapidly became important swimming predators. Their coiled shells and quickly evolving species later made them valuable fossils for dating marine rocks. Reef ecosystems also created protected lagoons, channels, slopes, and hard surfaces that increased the variety of available habitats.
Reef communities were severely affected during the Late Devonian biodiversity crisis. Large stromatoporoid-coral reef systems declined dramatically, and reef ecosystems did not return to the same scale for a long interval afterward.
Devonian Trilobites
Trilobites were no longer as diverse as they had been during the Cambrian and Ordovician, but they remained conspicuous members of many Devonian seafloor communities. Phacopid trilobites developed large, elevated schizochroal eyes made of relatively few separate lenses. Many could enroll tightly for protection, leaving the eyes and thickened shell exposed.
One of the most familiar North American Devonian trilobites is Eldredgeops rana, long known to collectors as Phacops rana. It is common in parts of the Middle Devonian Hamilton Group of New York and related rocks around the Great Lakes. Its broad head, rounded body, and prominent eyes make it easy to recognize.
Huntonia, also placed by some researchers in Huntoniatonia, is a striking Lower Devonian trilobite from Oklahoma. It had large eyes, a projecting snout-like front to the head, and long genal and tail spines. Complete specimens from the Haragan and Bois d'Arc formations are prized by collectors, although they require skilled preparation from hard limestone.
Other Devonian trilobites included Dipleura, Greenops, Paciphacops, Odontochile, Scutellum, and numerous proetids. Trilobite diversity declined during Middle and Late Devonian environmental crises. By the end of the period, all major groups except the proetids had disappeared.
The First Forests and Expanding Land Ecosystems
At the beginning of the Devonian, most land plants were small and lacked deep roots or broad leaves. By the Middle and Late Devonian, vegetation had changed dramatically. Many unrelated plant groups evolved into tall tree-sized plants, and the first known forests appeared along rivers, wetlands, and floodplains.
The famous Gilboa fossils of New York include cladoxylopsid trees with tall trunks and crowns of short branches. Nearby Middle Devonian fossil soils at Cairo preserve extensive root systems belonging to Archaeopteris, a tree with woody trunks, fern-like foliage, and deep, branching roots. Archaeopteris later became widespread and formed large forests across many parts of the world.
Forests changed the planet. Deep roots broke apart rock, stabilized riverbanks, created thicker soils, and increased the movement of nutrients into lakes and oceans. Growing vegetation stored carbon and caused a decline in atmospheric carbon dioxide.
Wildfires were also becoming part of these increasingly complex landscapes. Fossil charcoal occurs before the first true forests, but the spread of large woody plants during the Late Devonian provided much more fuel and made fire a more important ecological force. At the Red Hill fossil site in Pennsylvania, charcoal is interspersed with plant fossils, showing that fires burned within the surrounding floodplain vegetation.
Terrestrial arthropods also diversified. Mites, trigonotarbids, scorpions, millipedes and centipedes, and early insects lived in plant litter, soils, stream margins, and low vegetation. By the end of the Devonian, land ecosystems included producers, decomposers, herbivores, and predators, although they still lacked the flowering plants, birds, mammals, and reptiles familiar today.
The Fish-to-Tetrapod Transition
The fish-to-tetrapod transition did not begin with fishes suddenly walking onto land, as is commonly depicted. Instead, many of the important changes occurred while these animals were still living entirely in the water. Stronger appendages, flexible necks, flattened skulls, and air-breathing abilities would have been especially useful in shallow, crowded waterways filled with vegetation, submerged branches, and poorly oxygenated water.
Lobe-finned fishes, or sarcopterygians, played an important role in this transition. Unlike the thin, ray-supported fins of most fishes, their paired fins were fleshy and contained a chain of strong internal bones, including early counterparts of bones that later formed the tetrapod limb. The large Late Devonian lobe-finned fish Hyneria lindae was still fully aquatic, but its muscular, robust fins likely helped it turn, brace against the river bottom, and maneuver through the dense vegetation, submerged logs, and debris found in river systems such as Red Hill.
Hynerpeton bassetti, discovered at the Late Devonian Red Hill fossil site in Pennsylvania, was one of the earliest known tetrapods from North America. Its remains are incomplete, but they show that limbed vertebrates lived within the site's heavily vegetated river and floodplain ecosystem. Hynerpeton probably spent nearly all of its time in the water. Rather than using its limbs for walking on land, it probably used them to brace against the river bottom and navigate among aquatic plants, tangled branches, and submerged logs. Because a complete skeleton has not been found, its exact style of movement remains uncertain.
Tiktaalik roseae, from the Late Devonian of Arctic Canada, is an example of an earlier stage in this transition. It was still clearly a fish, with scales, gills, fins, and fin rays. However, its front fins contained bones comparable to a shoulder, elbow, and wrist, while its broad skull and mobile neck resembled features later seen in tetrapods.
Tiktaalik was an aquatic animal that lived in shallow channels and river-margin habitats. Its reinforced fins could allowed it to brace itself, lift part of its body, or push along the river bottom. These abilities would have been useful for moving through the vegetation and woody debris of these Devonian river systems.
Later forms such as Acanthostega and Ichthyostega had true limbs with digits, but they still retained many adaptations for aquatic life. Acanthostega was especially water-dependent, with a fishlike tail and limbs that could not support its full weight on land. Ichthyostega had a more robust skeleton and may have been capable of limited movement outside the water, although it would not have walked like a modern salamander or other land animal.
Together, these fossils show that limbs first became useful underwater in the densely vegetated, debris-strewn river systems of the Devonian. They could support the body in shallow water, help an animal push through dense vegetation, and provide leverage while moving over uneven river bottoms and around logs. Only later were tetrapod limbs modified for better movement across land.
Evidence for early tetrapods also comes from fossil footprints. The Valentia Island tetrapod trackways in Ireland were made during the late Middle Devonian, about 385 million years ago. Some of the trackways appear to record movement across exposed river-margin sediment, while others may have formed as the animals paddled or walked through shallow water. They show that early tetrapods could move through both shallow water and wet shoreline environments long before the best-known Late Devonian tetrapod skeletons appeared.
The fish-to-tetrapod transition was not a simple march from water onto land. It was a branching evolutionary process in which different types of animals developed different combinations of fishlike and tetrapod-like features. These experiments eventually produced vertebrates capable of living more permanently on land and gave rise to the lineage that later included amphibians, reptiles, birds, and mammals.
Late Devonian Environmental Crises and Extinctions
The Late Devonian biodiversity crisis was not one sudden event. It was a prolonged interval of ecological disruption containing several extinction pulses. The best known were the Kellwasser events near the Frasnian-Famennian boundary and the Hangenberg event close to the end of the Devonian.
Reef-building stromatoporoids and corals suffered severe losses, and many brachiopods, trilobites, ammonoids, conodonts, and fishes disappeared. Placoderms were among the vertebrate groups that failed to survive the final Devonian crises, while sharks and bony fishes passed through a major evolutionary bottleneck and later diversified in the Carboniferous.
Widespread marine anoxia, or severe oxygen depletion, was central to many of these events and is recorded by organic-rich black shales. The ultimate causes remain debated. Changes in climate and sea level, volcanic activity, nutrient runoff from increasingly deep-rooted forests, altered ocean circulation, and other factors may have interacted at different times.
The Hangenberg crisis near the Devonian-Carboniferous boundary affected both marine and freshwater ecosystems. Its aftermath reshaped vertebrate communities and marked the end of the ecological world that had made the Devonian the classic Age of Fishes.
Famous Fossil Sites from the Devonian Period
The Gogo Formation of Western Australia is one of the world's most important Devonian fish sites. Limestone concretions preserve three-dimensional fishes in extraordinary detail, including placoderms, early sharks, lungfishes, and other bony fishes. Some specimens preserve muscles, embryos, and umbilical structures, providing rare evidence of soft anatomy and reproduction.
The Rhynie Chert of Scotland preserves an Early Devonian hot-spring ecosystem in microscopic detail. Silica entombed plants, fungi, algae, microbes, mites, and other arthropods, often preserving cells and internal tissues. The deposit offers one of the clearest views of an early terrestrial ecosystem.
Miguasha in Quebec preserves Late Devonian fishes and plants from an ancient estuary. Its fossils include lobe-finned fishes, ray-finned fishes, placoderms, and the famous tetrapod relative Eusthenopteron. The site has played a major role in research on vertebrate evolution.
The Hunsruck Slate of Germany preserves Early Devonian marine animals in fine-grained sediment, sometimes with soft tissues and delicate appendages outlined by pyrite. Starfish, brittle stars, crinoids, trilobites, arthropods, worms, and fishes reveal details rarely preserved in ordinary marine rocks.
In North America, the Hamilton Group of New York and nearby states contains abundant Middle Devonian brachiopods, corals, crinoids, bryozoans, mollusks, and trilobites. The Silica Formation of Ohio is famous for well-preserved invertebrates, while the Cleveland Shale preserves Late Devonian fishes, including placoderms and sharks.
Red Hill in Pennsylvania preserves a Late Devonian floodplain ecosystem with fishes, plants, and early tetrapods. The Gilboa and Cairo fossil forests of New York record the rise of tree-sized vegetation and complex root systems. Other classic regions include the Old Red Sandstone of Scotland, the Anti-Atlas of Morocco, Devon and Cornwall in England, and Devonian reef complexes in western Canada and Australia.
Devonian Fossil Hunting Sites
Devonian rocks are exposed across many parts of eastern and central North America, and several Fossilguy guides cover productive collecting regions. Access, ownership, safety rules, and collecting regulations can change. Always verify current conditions, remain on legal access routes, and obtain permission before collecting on private property.
Western New York: Penn Dixie
The Western New York Devonian Fossil Guide covers Middle Devonian rocks of the Hamilton Group, including the Ludlowville and Moscow formations. These marine shales are known for brachiopods, corals, crinoids, bryozoans, mollusks, and trilobites including the classic Eldredgeops rana.
Mahantango Formation: Pennsylvania and West Virginia
The Mahantango Formation Fossil Guide covers Middle Devonian shale, siltstone, and sandstone exposures in Pennsylvania and West Virginia. The formation preserves brachiopods, bivalves, gastropods, corals, crinoids, bryozoans, and trilobite fragments including Dipleura, Eldredgeops, and Greenops.
Mahantango fossils occur at scattered roadcuts, stream exposures, and other outcrops rather than one single collecting park.
Sylvania, Ohio: Silica Formation and Fossil Park
The Sylvania Devonian Fossil Guide covers the Middle Devonian Silica Formation of northwestern Ohio. These fossil-rich shales are famous for brachiopods, corals, bryozoans, crinoids, mollusks, and occasional complete Eldredgeops trilobites.
The former Hanson quarry itself is not a public collecting site, however Fossil Park in Sylvania has quarry spoil material where people can search for fossils.
Recommended Devonian Books and Fossils
Gaining Ground, Second Edition: The Origin and Evolution of Tetrapods
Jennifer A. Clack: 2021
Etextbook: A detailed, scholarly look at the fish-to-tetrapod transition, covering lobe-finned fishes, early tetrapod anatomy, major fossil sites, and the move onto land. Technical at times, but clear and rewarding for serious paleontology readers.
The Trilobite Collector's Guide
Andy Secher, 2024
Written by leading trilobite collector Andy Secher, this guide offers a captivating journey into the world of these ancient arthorpods. It features more than 400 photos, collecting tips, top-ten lists, and advice for spotting fake trilobites.
References / Works Cited
Carmichael, S. K., Waters, J. A., Konigshof, P., Suttner, T. J., & Kido, E. (2019). Paleogeography and paleoenvironments of the Late Devonian Kellwasser Event: A review of its sedimentological and geochemical expression. Global and Planetary Change, 183, 102984. https://doi.org/10.1016/j.gloplacha.2019.102984
Daeschler, E. B., Shubin, N. H., & Jenkins, F. A., Jr. (2006). A Devonian tetrapod-like fish and the evolution of the tetrapod body plan. Nature, 440, 757-763. https://doi.org/10.1038/nature04639
International Commission on Stratigraphy. (2026). International Chronostratigraphic Chart, v2026/06. stratigraphy.org/chart
Meyer-Berthaud, B., Scheckler, S. E., & Wendt, J. (1999). Archaeopteris is the earliest known modern tree. Nature, 398, 700-701. https://doi.org/10.1038/19516
Sedgwick, A., & Murchison, R. I. (1839).
XL. Classification of the older stratified rocks of Devonshire and Cornwall.
The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science, 14(89), 241-260.
https://doi.org/10.1080/14786443908649732
Shubin, N. H., Daeschler, E. B., & Jenkins, F. A., Jr. (2006). The pectoral fin of Tiktaalik roseae and the origin of the tetrapod limb. Nature, 440, 764-771. https://doi.org/10.1038/nature04637
Stein, W. E., Berry, C. M., Hernick, L. V., & Mannolini, F. (2020). Mid-Devonian Archaeopteris roots signal revolutionary change in earliest fossil forests. Current Biology, 30, 421-431.e2. https://doi.org/10.1016/j.cub.2019.11.067
FAQs: Devonian Period Frequently Asked Questions
Quick answers to common questions about Devonian time, fossils, fishes, trilobites, forests, early tetrapods, climate, extinction events, and fossil collecting.
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When was the Devonian Period?
The Devonian Period lasted from about 419.62 to 358.86 million years ago. It was the fourth period of the Paleozoic Era, after the Silurian and before the Carboniferous.
See: Geologic Time -
Why is the Devonian called the Age of Fishes?
The Devonian is called the Age of Fishes because jawed vertebrates diversified into many forms, including armored placoderms, early sharks, ray-finned fishes, lobe-finned fishes, and lungfishes. These groups occupied marine and freshwater habitats and included some of the period's largest predators.
See: The Age of Fishes
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What lived during the Devonian Period?
Devonian seas contained placoderms, sharks, bony fishes, trilobites, brachiopods, corals, stromatoporoids, crinoids, ammonoids, and many other invertebrates. On land, the first forests expanded alongside early insects, arachnids, and other arthropods.
See: Life and Major Events -
When did the first forests appear?
The first known forests appeared during the Devonian. By the Middle and Late Devonian, tree-sized plants such as Archaeopteris had deep root systems, woody trunks, and broad crowns that transformed soils, rivers, weathering, and the global carbon cycle.
See: First Forests -
Did the first tetrapods evolve during the Devonian?
Yes. Devonian lobe-finned fishes gave rise to early tetrapods. Fossils such as Tiktaalik, Acanthostega, and Ichthyostega preserve different combinations of fish-like and tetrapod-like features and document a complex transition into shallow-water and terrestrial environments.
See: Fish-to-Tetrapod Transition -
What are the most common Devonian fossils?
Common Devonian fossils include brachiopods, corals, crinoid stem pieces, bryozoans, mollusks, and trilobite fragments. Fish plates, teeth, and scales can be common in some formations, while complete fishes and complete trilobites are much less common.
See: Devonian Life and Fossils -
What trilobites lived during the Devonian?
Devonian trilobites included phacopids such as Eldredgeops, commonly called Phacops, and distinctive forms such as Huntonia. Proetid trilobites also remained widespread and were the only trilobite group to survive beyond the Devonian.
See: Devonian Trilobites -
What was Earth's climate like during the Devonian?
Much of the Devonian had a warm greenhouse climate with extensive tropical seas, but conditions changed through time. Expanding forests, falling carbon dioxide, shifting sea levels, ocean anoxia, and episodes of cooling contributed to major environmental changes.
See: Devonian Earth and Climate -
What caused the Late Devonian extinctions?
The Late Devonian biodiversity crisis included several extinction pulses, especially the Kellwasser and Hangenberg events. Widespread low-oxygen seas were important, but the ultimate causes remain debated and may have involved climate change, volcanism, nutrient runoff, sea-level changes, and the expansion of land plants.
See: Late Devonian Extinctions -
Where can you collect Devonian fossils?
Fossilguy guides cover Devonian collecting areas in western New York, the Mahantango Formation of Pennsylvania and West Virginia, and the Silica Formation near Sylvania, Ohio. Access rules change, so collectors should verify current regulations and obtain permission before visiting any site.
See: Devonian Fossil Hunting Sites
Jump to Sections
Fast Facts | Geologic Time | Discovery and Naming | Earth and Climate | Life and Events | Age of Fishes | Reefs | Devonian Trilobites | First Forests | Early Tetrapods | Extinction Events | Famous Fossil Sites | Fossil Hunting Sites | Books | References | FAQ
