Devonian

The Devonian is the Silurian, 419.2 million years ago Mya, to the beginning of the Carboniferous, 358.9 Mya. it is named after Devon, England, where rocks from this period were first studied.

The first significant adaptive radiation of life on dry land occurred during the Devonian. Free-sporing vascular plants began to spread across dry land, forming extensive forests which returned the continents. By the middle of the Devonian, several groups of plants had evolved leaves together with true roots, & by the end of the period the first seed-bearing plants appeared. The arthropod groups of myriapods, arachnids and hexapods also became well-established early on in this period, after having started their expansion to land at least from the Ordovician period.

Late Ordovician.

The first Proetida.

The palaeogeography was dominated by the supercontinent of Gondwana to the south, the small continent of Siberia to the north, and the early outline of the medium-sized continent of Euramerica in between.

Life

Sea levels in the Devonian were broadly high. Marine faunas continued to be dominated by bryozoa, diverse and abundant brachiopods, the enigmatic hederellids, microconchids and corals. Lily-like crinoids animals, their resemblance to flowers notwithstanding were abundant, and trilobites were still fairly common. Among vertebrates, jawless armored fish ostracoderms declined in diversity, while the jawed fish gnathostomes simultaneously increased in both the sea and fresh water. Armored placoderms were many during the lower stages of the Devonian Period and became extinct in the gradual Devonian, perhaps because of competition for food against the other fish species. Early cartilaginous Chondrichthyes and bony fishes Osteichthyes also become diverse and played a large role within the Devonian seas. The first abundant genus of shark, Cladoselache, appeared in the oceans during the Devonian Period. The great diversity of fish around at the time has led to the Devonian being given the draw "The Age of Fish" in popular culture.

The first ammonites also appeared during or slightly previously the early Devonian Period around 400 Mya.

A now-dry barrier reef, located in present-day carbonate-secreting organisms that hold the ability to erect wave-resistant managers close to sea level. Although modern reefs are constructed mainly by corals and calcareous algae, Devonian reefs were either microbial reefs built up mostly by autotrophic cyanobacteria, or coral-stromatoporoid reefs built up by coral-like stromatoporoids and tabulate and rugose corals. Microbial reefs dominated under the warmer conditions of the early and unhurried Devonian, while coral-stromatoporoid reefs dominated during the cooler middle Devonian.

By the Devonian Period, life was alive underway in its colonisation of the land. The insects appeared around 416 Mya, in the Early Devonian. Evidence for the earliest tetrapods takes the form of trace fossils in shallow lagoon settings within a marine carbonate platform / shelf during the Middle Devonian, although these traces have been questioned and an interpretation as fish feeding traces Piscichnus has been advanced.

Many Early Devonian plants did not have true roots or leaves like extant plants although vascular tissue is observed in numerous of those plants. Some of the early land plants such as Drepanophycus likely spread by vegetative growth and spores. The earliest land plants such(a) as Cooksonia consisted of leafless, dichotomous axes and terminal sporangia and were loosely very short-statured, and grew hardly more than a few centimetres tall. Fossils of Armoricaphyton chateaupannense, about 400 million years old, equal the oldest invited plants with woody tissue. By the Middle Devonian, shrub-like forests of primitive plants existed: lycophytes, horsetails, ferns, and progymnosperms evolved. near of these plants had true roots and leaves, and many were quite tall. The earliest-known trees appeared in the Middle Devonian. These specified a lineage of lycopods and another arborescent, woody vascular plant, the cladoxylopsids and progymnosperm Archaeopteris. These tracheophytes were professional to grow to large size on dry land because they had evolved the ability to biosynthesize lignin, which gave them physical rigidity and modernizing the effectiveness of their vascular system while giving them resistance to pathogens and herbivores. These are the oldest-known trees of the world's first forests. By the end of the Devonian, the first seed-forming plants had appeared. This rapid layout of so many plant groups and growth forms has been called the "Devonian Explosion".

The 'greening' of the continents acted as a carbon sink, and atmospheric concentrations of carbon dioxide may have dropped. This may have cooled the climate and led to a massive extinction event. See Late Devonian extinction.

Lycopod axis branch from the Middle Devonian of Wisconsin

Bark possibly from a cladoxylopsid from the Middle Devonian of Wisconsin

Primitive arthropods co-evolved with this diversified terrestrial vegetation structure. The evolving co-dependence of insects and seed-plants that characterised a recognisably innovative world had its genesis in the Late Devonian Epoch. The development of soils and plant root systems probably led to reorientate in the speed and sample of erosion and sediment deposition. The rapid evolution of a terrestrial ecosystem that contained copious animals opened the way for the first vertebrates to seek out a terrestrial living. By the end of the Devonian, arthropods were solidly established on the land.

Dunkleosteus, one of the largest armoured fish ever to roam the planet, lived during the Late Devonian

Lower jaw of Eastmanosteus pustulosus from the Middle Devonian of Wisconsin

Tooth of the lobe-finned fish Onychodus from the Middle Devonian of Wisconsin

Early shark Cladoselache, several lobe-finned fishes, including Eusthenopteron that was an early marine tetrapod, and the placoderm Bothriolepis in a painting from 1905

Melocrinites nodosus spinosus, a spiny, stalked crinoid from the Middle Devonian of Wisconsin

Enrolled phacopid trilobite from the Devonian of Ohio

The common tabulate coral Aulopora from the Middle Devonian of Ohio – idea of colony encrusting a brachiopod valve

Tropidoleptus carinatus, an orthid brachiopod from the Middle Devonian of New York

Pleurodictyum americanum, Kashong Shale, Middle Devonian of New York

SEM view of a hederelloid from the Devonian of Michigan largest tube diameter is 0.75 mm

Devonian spiriferid brachiopod from Ohio which served as a host substrate for a colony of hederelloids