4.4 Devonian period
9 min read•august 20, 2024
The Devonian period, spanning 419.2 to 358.9 million years ago, was a crucial time in Earth's history. Known as the "," it saw rapid diversification of marine life, the emergence of the first forests, and significant changes in the planet's atmosphere and climate.
This period witnessed the formation of supercontinents, widespread shallow seas, and a generally warm climate. The Devonian's most notable developments include the evolution of vascular plants, the rise of the first forests, and the appearance of , setting the stage for vertebrate colonization of land.
Devonian period overview
- Occurred approximately 419.2 to 358.9 million years ago, following the Silurian and preceding the Carboniferous periods in the Paleozoic Era
- Characterized by the rapid diversification of fish, the appearance of the first forests, and significant changes in the Earth's atmosphere and climate
- Marked by two major extinction events at the end of the period, which significantly impacted marine life
Age of fishes
Top images from around the web for Age of fishes
Amphibians | Biology I View original
Is this image relevant?
Evolution of fish - Wikipedia View original
Is this image relevant?
Fish reared on land replay the transition to four legs | Readable View original
Is this image relevant?
Amphibians | Biology I View original
Is this image relevant?
Evolution of fish - Wikipedia View original
Is this image relevant?
1 of 3
Top images from around the web for Age of fishes
Amphibians | Biology I View original
Is this image relevant?
Evolution of fish - Wikipedia View original
Is this image relevant?
Fish reared on land replay the transition to four legs | Readable View original
Is this image relevant?
Amphibians | Biology I View original
Is this image relevant?
Evolution of fish - Wikipedia View original
Is this image relevant?
1 of 3
- The Devonian is often referred to as the "Age of Fishes" due to the remarkable diversification and evolution of fish during this time
- , , and all underwent significant adaptive radiations
- The period also saw the emergence of the , four-limbed vertebrates that would eventually give rise to amphibians and all other land vertebrates
Temporal range
- The Devonian spans a time interval of approximately 60.3 million years
- Subdivided into three epochs: the (419.2 to 393.3 Ma), (393.3 to 382.7 Ma), and (382.7 to 358.9 Ma)
- Each epoch is further divided into stages based on the appearance and disappearance of specific fossils and changes in the global environment
Devonian paleogeography
- The Devonian was characterized by the continued breakup of the supercontinent and the formation of the supercontinent Euramerica (also known as )
- The collision of Laurussia and Gondwana began in the Late Devonian, eventually leading to the formation of the supercontinent Pangaea in the Permian
Laurussia vs Gondwana
- Laurussia formed from the collision of the Laurentian and Baltic cratons during the Caledonian in the Early Devonian
- Gondwana, which included modern-day Africa, South America, Australia, Antarctica, and India, was located in the southern hemisphere
- The two supercontinents were separated by the , which progressively closed during the Devonian due to the convergence of Laurussia and Gondwana
Shallow seas
- Much of Laurussia and parts of Gondwana were covered by shallow, warm seas during the Devonian
- These epicontinental seas provided habitat for diverse marine life, including reef-building organisms like stromatoporoids and corals
- Fluctuations in sea level throughout the Devonian led to the repeated flooding and exposure of continental shelves, influencing sediment deposition and fossil preservation
Devonian climate
- The Devonian climate was generally warm and humid, with atmospheric CO2 levels estimated to be several times higher than present-day levels
- The period began with but experienced a gradual cooling trend, culminating in a brief glacial episode near the end of the Devonian
Greenhouse conditions
- The Early Devonian was characterized by a greenhouse climate, with high atmospheric CO2 levels and global temperatures
- Lack of significant continental glaciation and the presence of tropical flora and fauna at high latitudes provide evidence for these warm conditions
- Greenhouse conditions likely facilitated the expansion of vascular plants and the development of the first forests
Glaciation evidence
- Despite the overall warm climate, evidence suggests a brief glacial episode occurred during the Late Devonian
- Glacial deposits have been found in South America and Africa, indicating the presence of ice sheets on parts of Gondwana
- The onset of glaciation may have been triggered by a drawdown of atmospheric CO2 levels, possibly linked to the rise of vascular plants and increased weathering rates
Devonian flora
- The Devonian saw the rapid evolution and diversification of vascular plants, which had first appeared in the Silurian
- Early Devonian flora was dominated by small, herbaceous plants, but by the Late Devonian, the first forests had emerged, transforming terrestrial ecosystems
Early vascular plants
- Early Devonian vascular plants were small and lacked true roots and leaves, relying on rhizoids for anchorage and sporangia for reproduction
- Genera such as Cooksonia and Rhynia represent some of the earliest known vascular plants
- As the Devonian progressed, plants evolved more complex vascular systems, true roots, leaves, and secondary growth, enabling them to grow taller and colonize new habitats
Archaeopteris forests
- By the Late Devonian, the first forests had appeared, dominated by the tree-like lycophyte Archaeopteris
- Archaeopteris could grow up to 30 meters tall and had a woody trunk, true leaves, and an extensive root system
- The rise of had significant impacts on the global carbon cycle, weathering rates, and atmospheric composition, potentially contributing to the Late Devonian extinction events
Devonian fauna
- The Devonian is renowned for the diversification of fish and the appearance of the first tetrapods, but the period also saw the continued evolution of invertebrate life
- Marine ecosystems were dominated by placoderms, lobe-finned fishes, and ray-finned fishes, while invertebrates such as trilobites, brachiopods, and crinoids remained abundant
Placoderms
- Placoderms were a diverse group of armored fishes that dominated Devonian seas
- They were characterized by bony plates covering their head and thorax, and some species, such as Dunkleosteus, grew to massive sizes (up to 10 meters long)
- Placoderms went extinct at the end of the Devonian, possibly due to competition with other fish groups or the Late Devonian extinction events
Lobe-finned fishes
- Lobe-finned fishes, or sarcopterygians, include the ancestors of tetrapods as well as the coelacanths and lungfishes
- They are characterized by fleshy, lobed fins containing bones homologous to those in the limbs of tetrapods
- During the Devonian, lobe-finned fishes diversified and gave rise to the first tetrapods, which began to venture onto land
Ray-finned fishes
- Ray-finned fishes, or actinopterygians, are the most diverse group of vertebrates today, encompassing nearly all modern fish species
- In the Devonian, ray-finned fishes underwent a major adaptive radiation, evolving a wide range of body forms and feeding strategies
- Notable Devonian ray-finned fishes include the predatory Cheirolepis and the deep-bodied Mimipiscis
Early tetrapods
- The first tetrapods, or four-limbed vertebrates, evolved from lobe-finned fishes during the Late Devonian
- genera such as Acanthostega and Ichthyostega had a mix of fish-like and tetrapod features, including gills, fins, and primitive lungs
- These early tetrapods were still primarily aquatic but had the ability to venture onto land, setting the stage for the vertebrate colonization of terrestrial habitats
Invertebrate diversity
- Devonian seas hosted a diverse array of invertebrate life, including trilobites, brachiopods, mollusks, and echinoderms
- Trilobites, which had dominated Paleozoic seas, began to decline in diversity during the Devonian, possibly due to competition with other arthropods and fish
- Brachiopods and reef-building organisms like stromatoporoids and tabulate corals were abundant in environments
Devonian mass extinctions
- The Devonian Period is marked by several extinction events, the most significant being the Late Devonian extinction
- These extinctions had profound impacts on marine ecosystems, leading to the disappearance of many iconic Devonian taxa
Late Devonian extinction
- The Late Devonian extinction was a prolonged series of extinction pulses that occurred over several million years, culminating in the Hangenberg Event at the Devonian-Carboniferous boundary
- It is estimated that up to 70% of marine species went extinct during this time, including all placoderms, many trilobites, and numerous brachiopod and coral species
- The extinction disproportionately affected shallow marine ecosystems, particularly reef communities
Causes of extinctions
- The causes of the Late Devonian extinction are still debated, but several factors likely contributed:
- Global cooling and glaciation, which lowered sea levels and disrupted marine habitats
- Reduced oxygen levels in the oceans, possibly due to eutrophication from the spread of vascular plants on land
- Volcanic activity and associated changes in atmospheric composition and climate
- The evolution of land plants, which altered weathering rates and nutrient cycling
- The combination of these factors likely placed significant stress on marine ecosystems, leading to the observed extinction patterns
Devonian reef systems
- Devonian seas were characterized by extensive reef systems, which hosted diverse communities of marine organisms
- Reefs were constructed primarily by stromatoporoids and tabulate corals, with contributions from other organisms such as rugose corals, bryozoans, and calcareous algae
Stromatoporoid reefs
- Stromatoporoids, a group of sponge-like organisms, were the dominant reef-builders in the Devonian
- They formed large, mound-like structures that provided habitat for a wide range of marine life
- Stromatoporoid reefs were particularly abundant in the shallow, warm seas that covered much of Laurussia during the Devonian
Coral reefs
- Tabulate and rugose corals also played a significant role in Devonian reef construction
- Tabulate corals, named for their table-like appearance, formed large colonies that contributed to reef growth
- Rugose corals, also known as horn corals, were solitary or colonial and added to the structural complexity of Devonian reefs
- The Late Devonian extinction events had a severe impact on reef communities, leading to the collapse of many reef systems
Devonian geology
- The Devonian Period is represented by a wide range of sedimentary and volcanic rocks, reflecting the diverse environments and tectonic settings of the time
- Two notable geological formations from the Devonian are the and the
Old Red Sandstone
- The Old Red Sandstone is a sequence of sedimentary rocks, primarily sandstones and conglomerates, that were deposited in non-marine environments during the Devonian
- These rocks are found in many parts of Europe and North America and are often red in color due to the presence of iron oxides
- The Old Red Sandstone preserves a rich fossil record of Devonian fish and early tetrapods, as well as trace fossils of terrestrial arthropods
Catskill Delta
- The Catskill Delta was a large, prograding delta system that formed along the eastern coast of Laurussia during the Late Devonian
- It is composed of a thick sequence of sandstones, shales, and conglomerates that were deposited in fluvial, estuarine, and shallow marine environments
- The Catskill Delta preserves a diverse fossil assemblage, including , freshwater fish, and some of the earliest known tetrapod remains
Economic resources
- Devonian rocks are important sources of economic resources, particularly hydrocarbons such as oil and natural gas
- These resources are often associated with organic-rich shales that were deposited in anoxic marine environments during the Devonian
Devonian oil shales
- Devonian oil shales are fine-grained sedimentary rocks that contain significant amounts of organic matter, which can be converted into oil through heating
- Major Devonian oil shale deposits are found in the United States (e.g., the Green River Formation) and Estonia
- The high organic content of these shales is attributed to the abundant marine life and anoxic conditions that prevailed in many Devonian seas
Devonian gas reserves
- Devonian shales are also important sources of natural gas, particularly in North America
- The Marcellus Shale, which underlies parts of the Appalachian Basin in the eastern United States, is one of the largest natural gas plays in the world
- Other significant Devonian gas reserves are found in the Barnett Shale of Texas and the Horn River Basin of Canada
- The development of horizontal drilling and hydraulic fracturing technologies has made the extraction of gas from these shales economically viable
Devonian in the fossil record
- The Devonian Period is well-represented in the fossil record, with a diverse array of marine and terrestrial organisms preserved in sedimentary rocks worldwide
- Some Devonian fossil sites are known for their exceptional preservation, providing unique insights into the anatomy and ecology of ancient life
Exceptional preservation
- Exceptional preservation refers to fossil sites where organisms are preserved with fine anatomical details, such as soft tissues, that are not typically fossilized
- Devonian sites with exceptional preservation include the of Germany, which preserves pyritized soft-bodied organisms, and the Gogo Formation of Australia, known for its three-dimensionally preserved fish fossils
- These sites offer rare glimpses into the biology of Devonian organisms and help paleontologists reconstruct ancient ecosystems
Lagerstätten deposits
- Lagerstätten (singular: Lagerstätte) are fossil deposits characterized by their exceptional preservation, diversity, and/or abundance of fossils
- Notable Devonian Lagerstätten include:
- The Rhynie Chert of Scotland, which preserves early vascular plants and terrestrial arthropods in exquisite detail
- The Miguasha National Park in Quebec, Canada, renowned for its diverse assemblage of Devonian fish, including early tetrapods
- The Cleveland Shale of Ohio, USA, which has yielded numerous well-preserved shark and placoderm fossils
- These Lagerstätten provide invaluable windows into Devonian life and have greatly contributed to our understanding of the period's biodiversity and evolutionary history
Key Terms to Review (30)
Age of Fishes: The Age of Fishes refers to the Devonian period, a time spanning from about 419 to 359 million years ago, when fish flourished and diversified in marine environments. This era saw the emergence of various fish groups, including early jawed fishes and lobe-finned fishes, which played a crucial role in the evolution of vertebrates. It marked significant advancements in fish anatomy and ecology, setting the stage for future vertebrate life on land.
Archaeopteris forests: Archaeopteris forests were ancient woodlands that thrived during the late Devonian period, characterized by the dominance of the genus Archaeopteris, a tree-like plant that exhibited both fern-like and seed plant features. These forests played a crucial role in transforming terrestrial ecosystems, marking a significant transition from primitive vegetation to more complex forest structures, which influenced soil formation and atmospheric composition.
Catskill Delta: The Catskill Delta refers to a geologic formation that was primarily created during the late Devonian period, characterized by extensive river and deltaic systems that deposited sediment in the region of present-day New York. This delta was significant for its role in shaping the paleoenvironments of the time, influencing both terrestrial and aquatic life through sedimentation patterns and habitat formation.
David Attenborough: David Attenborough is a renowned British broadcaster and natural historian, best known for his influential work in the field of wildlife documentaries. His passion for nature and the environment has inspired generations to appreciate the natural world, making him a pivotal figure in the conversation about biodiversity and conservation. Through his engaging storytelling and visually stunning films, he has brought attention to various aspects of evolution, including the development of vertebrates during the Devonian period, the evolution of birds from dinosaurs, mammalian diversification, and the role of echinoderms in marine ecosystems.
Devonian Biodiversity Crisis: The Devonian Biodiversity Crisis refers to a significant and widespread decline in marine and terrestrial biodiversity that occurred during the Late Devonian period, approximately 375 million years ago. This crisis is characterized by the extinction of numerous species, particularly among marine life like corals and certain fish groups, significantly impacting the ecosystem dynamics of the time. The causes of this crisis are believed to include climate change, anoxia in oceanic waters, and changes in sea level.
Early devonian: The Early Devonian is the first stage of the Devonian Period, lasting from about 419 to 393 million years ago. This time was marked by significant evolutionary advancements, especially in marine life, and the emergence of early terrestrial ecosystems, laying the groundwork for major changes in biodiversity and habitat development.
Early tetrapods: Early tetrapods were the first vertebrates to make the transition from aquatic to terrestrial environments, evolving during the Devonian period. This transition marked a significant evolutionary milestone, as these creatures developed key adaptations that enabled them to navigate land, such as limbs instead of fins and changes in respiratory systems. Early tetrapods played a crucial role in the evolution of amphibians and other land-dwelling vertebrates.
Early vascular plants: Early vascular plants were among the first land plants to develop specialized tissues for transporting water and nutrients, marking a significant evolutionary step in plant life during the Devonian period. These plants were crucial for colonizing terrestrial environments, as they could grow taller and thrive in diverse habitats, contributing to the establishment of complex terrestrial ecosystems.
First tetrapods: The first tetrapods were the earliest vertebrate animals that transitioned from aquatic to terrestrial environments, marking a significant evolutionary milestone during the Devonian period. These organisms, which include ancestors of modern amphibians, reptiles, birds, and mammals, adapted to life on land by developing limbs and other physiological changes that allowed them to thrive outside water. Their emergence represents a critical step in the evolution of vertebrates as they moved into new habitats and diversified into various lineages.
First true trees: First true trees refer to the earliest large, woody plants that appeared during the Devonian period, characterized by their ability to grow tall and form complex branching structures. These trees played a vital role in transforming terrestrial ecosystems by providing habitats and influencing soil formation. They represented a significant evolutionary advancement in plant life, showcasing the ability to photosynthesize efficiently and store resources, which ultimately paved the way for modern forests.
Frasnian-Famennian Extinction: The Frasnian-Famennian extinction was a significant event that occurred at the end of the Devonian period, around 372 million years ago, leading to a major loss of biodiversity on Earth. This extinction is particularly notable for the dramatic reduction in marine life, including various fish and coral species, marking one of the five largest mass extinction events in Earth's history. It resulted in substantial ecological shifts and paved the way for the evolution of new species in the following periods.
Glaciation Evidence: Glaciation evidence refers to geological and climatic indicators that demonstrate the past existence of glaciers and ice sheets on Earth's surface. This evidence can include various features such as striations, moraines, and till deposits, which provide insight into historical climate conditions, landforms, and the movement of glaciers during periods of glaciation, particularly during significant ice ages.
Gondwana: Gondwana was a supercontinent that existed from the Late Precambrian to the Jurassic period, comprising landmasses that are now part of Africa, South America, Antarctica, Australia, and the Indian subcontinent. This massive landmass played a crucial role in shaping the geological and biological history of Earth, particularly influencing the evolution and distribution of species during various geological periods.
Graham Young: Graham Young was a notable figure during the Devonian period, recognized for his contributions to paleontology and our understanding of ancient life. His work primarily focused on the study of fossil records and the biological diversity that thrived during this geological era, which is often referred to as the 'Age of Fishes'. Young's research provided insights into the evolutionary patterns and environmental changes that occurred throughout the Devonian period, significantly enhancing our knowledge of vertebrate development.
Greenhouse conditions: Greenhouse conditions refer to an atmospheric state where elevated levels of greenhouse gases, such as carbon dioxide and methane, lead to increased heat retention within the Earth's atmosphere. This phenomenon significantly influences global temperatures and climate patterns, affecting ecosystems and life forms during various geological periods, including the Devonian period.
Hunsrück Slate: The Hunsrück Slate is a geologic formation from the Devonian period, primarily located in the Hunsrück region of Germany. It is known for its exceptional fossil preservation and rich deposits of various marine organisms, providing crucial insights into early Paleozoic life and ecosystems. This slate is significant for understanding the biodiversity and environmental conditions of the Devonian seas, making it a key site for paleontological research.
Invertebrate Diversity: Invertebrate diversity refers to the wide range of species, forms, and ecological roles of invertebrates, which are animals without a backbone. This diversity includes various groups such as arthropods, mollusks, and cnidarians, showcasing a multitude of adaptations that allow these organisms to thrive in different environments. Invertebrates play crucial roles in ecosystems, from pollination to decomposition, highlighting their significance in both ancient and modern ecological systems.
Jaw evolution: Jaw evolution refers to the development of jaws in vertebrates, transforming the way they feed and interact with their environment. This crucial adaptation allowed early vertebrates to exploit a wider range of food sources, leading to significant diversification and complexity in aquatic ecosystems. The evolution of jaws is particularly linked to major periods in Earth's history, which saw the emergence of various fish species and set the stage for further vertebrate adaptations.
Late Devonian: The Late Devonian is the final stage of the Devonian period, spanning from approximately 383 to 359 million years ago. This time is marked by significant geological, climatic, and biological changes, including the diversification of fish, the emergence of early amphibians, and substantial shifts in marine environments, leading to one of the largest mass extinctions in Earth's history.
Laurussia: Laurussia refers to a supercontinent that formed during the late Paleozoic Era, primarily consisting of present-day North America and Europe. It played a crucial role in shaping the Earth's geological and biological landscape during significant periods such as the Devonian and Carboniferous, contributing to changes in climate, sea levels, and the distribution of flora and fauna.
Lobe-finned fishes: Lobe-finned fishes are a group of bony fish characterized by their fleshy, lobed fins, which are joined to the body by a single bone. These fishes, including the coelacanths and lungfishes, represent a significant evolutionary link between fish and the early tetrapods that eventually ventured onto land. Their unique fin structure provides insight into the transition from aquatic to terrestrial life during the Devonian period.
Middle Devonian: The Middle Devonian is a subdivision of the Devonian period, occurring approximately 393 to 383 million years ago. This time frame is marked by significant geological and biological developments, including the diversification of fish and the emergence of early terrestrial ecosystems. The Middle Devonian is crucial for understanding evolutionary trends and the global changes that shaped the Earth's environments during this period.
Old Red Sandstone: Old Red Sandstone refers to a series of sedimentary rock formations primarily composed of reddish sandstone, which were deposited during the Late Silurian to Early Devonian periods. These rocks are significant for understanding the geological and paleontological history of this time, particularly as they contain important fossils that shed light on the early evolution of fish and terrestrial life.
Orogeny: Orogeny is the process of mountain formation, particularly through tectonic plate interactions, including collisions and subductions. This geological phenomenon results in the uplift and deformation of Earth's crust, significantly shaping landscapes and influencing ecological and climatic conditions over geological time. Orogeny is crucial in understanding the formation of mountain ranges and their effects on biodiversity and natural resources.
Placoderms: Placoderms were an ancient group of armored fish that lived during the Paleozoic era, particularly thriving in the Devonian period. They are characterized by their bony plates that covered their head and thorax, giving them a distinctive appearance compared to modern fish. As some of the earliest jawed vertebrates, placoderms played a crucial role in the evolution of vertebrate life and are often associated with significant ecological changes during their time.
Ray-finned fishes: Ray-finned fishes are a diverse group of bony fish characterized by their fin structure, where the fins are supported by bony rays. They are the most abundant and diverse class of vertebrates, thriving in various aquatic environments. These fishes emerged during the Devonian period, which marked a significant evolutionary milestone as they adapted to numerous ecological niches, leading to their dominance in modern aquatic ecosystems.
Rheic Ocean: The Rheic Ocean was a major oceanic body that existed during the Paleozoic Era, particularly prominent during the Devonian period. This ocean played a crucial role in the geological and paleogeographical evolution of the Earth, acting as a connecting body of water between the northern and southern continents, including Laurussia and Gondwana. The Rheic Ocean significantly influenced marine life and sedimentation patterns, making it an essential feature in understanding the Earth's ancient environments.
Sedimentation: Sedimentation is the process by which particles settle out of a fluid and accumulate over time, forming layers of sediment. This process is essential in the formation of sedimentary rocks and plays a critical role in preserving fossils, as it provides the medium in which organic materials can be buried and later transformed into fossils. The rate and conditions of sedimentation influence the distortion and alteration of fossils, the geologic record of specific periods like the Devonian, and the characteristics of terrestrial environments.
Shallow marine: Shallow marine refers to the areas of the ocean that are relatively close to shore and typically characterized by shallow waters, often less than 200 meters deep. These environments are crucial for various ecological processes and play a significant role in sediment deposition, biodiversity, and fossil formation, especially during specific geological periods.
Terrestrial colonization: Terrestrial colonization refers to the process by which organisms, particularly plants and animals, adapt and establish themselves in terrestrial environments. This shift from aquatic to land habitats was a significant evolutionary step during the Devonian period, leading to the development of diverse ecosystems and a variety of terrestrial life forms.