Devonian Period (about 419–359 million years ago)
The Devonian is a geologic period in the Paleozoic marked by diverse marine life, the rise of forests and seed plants, and the first vertebrates venturing onto land — a key chapter in early terrestrial ecosystems.
Overview
The Devonian is the fourth period of the Paleozoic and a major interval within the Phanerozoic eon, spanning roughly from 419 to 359 million years ago. The name derives from Devonshire, in England, where characteristic rocks of this age were first studied. The period is often called the "Age of Fishes" because of the remarkable diversification of aquatic vertebrates, but it is also notable for major innovations on land.
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Environment and characteristic life
High global sea levels flooded many continental margins and produced widespread shallow marine habitats. These conditions supported extensive reefs and diverse marine communities. Key groups of Devonian fish included:
- Agnatha (jawless fishes)
- Acanthodii (spiny fishes)
- Placoderms (armoured fishes)
- Chondrichthyes (cartilaginous fishes: early relatives of sharks and rays)
- Osteichthyes (bony fishes), including the lobe-finned fishes closely related to tetrapods
On land, plants made a dramatic advance: small vascular plants gave rise to taller forms, forests of tree-like lycopsids, horsetails and early ferns developed, and the first seed-bearing plants emerged. Arthropods such as primitive insects and myriapods also became established in terrestrial environments.
Continental layout and climate
The arrangement of continents differed markedly from today. The great southern landmass Gondwana dominated the high southern latitudes, while smaller continents such as Siberia and pieces of what would become Europe and North America occupied other positions. The proto-continent Euramerica lay nearer the equator and provided many of the shallow seas that supported reefs. Toward the end of the Devonian these plates were converging and the first steps toward assembling Pangaea were underway. Climate varied through the period but overall patterns fostered warm shallow seas and widespread vegetated land surfaces.
Stratigraphy and subdivisions
Geologists divide Devonian rock sequences into lower, middle and upper units to reflect changes in fossils and environments. These Devonian strata preserve marine shelf sediments, reef complexes, and terrestrial deposits that capture the growing complexity of ecosystems. Regional rock successions and fossil assemblages allow finer subdivisions and correlations across continents.
Evolutionary significance and terrestrial colonization
The Devonian witnessed several evolutionary milestones. Fish evolved new jaw structures, fins and sensory systems, and some lobe-finned fishes made the transition toward limb-bearing forms. The broader process of evolution of vertebrates from water to land involved fishes (fish) that show a mix of aquatic and terrestrial features; transitional fossils (for example, well-known taxa sometimes cited in popular summaries) illustrate stages on the path to true tetrapods. At the same time, terrestrial ecosystems matured as arthropods diversified and plants stabilized soils and altered global biogeochemical cycles.
Notable events and legacy
The Devonian ended with one or more extinction pulses that disproportionately affected marine communities, particularly reef-builders and many fish groups. The causes are debated and likely include sea-level change, climate shifts and ecological stress. Despite losses, the evolutionary innovations of the Devonian — forests, seeds, complex freshwater and nearshore food webs, and the origin of tetrapods — shaped the later history of life and paved the way for terrestrial dominance by vertebrates and land plants.
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Questions and answers
Q: What period of the Paleozoic era is the Devonian?
A: The Devonian is the fourth period of the Paleozoic era.
Q: When did the Devonian period last?
A: The Devonian period lasted from about 419 million years ago (mya) to about 359 mya.
Q: Where was it named after?
A: The Devonian was named after Devonshire, England, where rocks from this period were first studied.
Q: What type of fish existed during this time?
A: During the Devonian, various types of fish existed including Agnatha (jawless fish), Acanthodii (spiny fish), Placoderms (armoured fish), Chondrichthyes (cartilaginous fish), and early Osteichthyes (bony fish).
Q: What other organisms evolved during this time?
A: During the Devonian, evolution of fish into tetrapods occurred and various terrestrial arthropods also became established. Additionally, seed-bearing plants spread across dry land forming huge forests.
Q: What continents were present during this time?
A: During the Devonian, there was a supercontinent of Gondwana to the south and Siberia to the north with an early form of Euramerica in between them. Pangaea was just starting to form at that time as well.
Q: How had land been colonized by late in this period? A: By late in the Devonian period, land had been colonized by plants and insects while massive reefs were built in oceans. Additionally, Euramerica and Gondwana were beginning to converge into what would become Pangaea.
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Author
AlegsaOnline.com Devonian Period (about 419–359 million years ago) Leandro Alegsa
URL: https://en.alegsaonline.com/art/26993