Portal:Devonian

The Devonian Portal

A map of Earth as it appeared 390 million years ago during the Middle Devonian Epoch

The Devonian (/dəˈvoʊni.ən, dɛ-/ də-VOH-nee-ən, deh-) is a geologic period and system of the Paleozoic era during the Phanerozoic eon, spanning 60.7 million years from the end of the preceding Silurian period at 419.62 million years ago (Ma), to the beginning of the succeeding Carboniferous period at 358.86 Ma. It is the fourth period of both the Paleozoic and the Phanerozoic. It is named after Devon, South West England, where rocks from this period were first studied.

The first significant evolutionary radiation of life on land occurred during the Devonian, as free-sporing land plants (pteridophytes) began to spread across dry land, forming extensive coal forests which covered the continents. By the middle of the Devonian, several groups of vascular plants had evolved leaves and true roots, and by the end of the period the first seed-bearing plants (pteridospermatophytes) appeared. This rapid evolution and colonization process, which had begun during the Silurian, is known as the Silurian-Devonian Terrestrial Revolution. The earliest land animals, predominantly arthropods such as myriapods, arachnids and hexapods, also became well-established early in this period, after beginning their colonization of land at least from the Ordovician Period.

Fish, especially jawed fish, reached substantial diversity during this time, leading the Devonian to be called the Age of Fishes. The armored placoderms began dominating almost every known aquatic environment. In the oceans, cartilaginous fishes such as primitive sharks became more numerous than in the Silurian and Late Ordovician. Tetrapodomorphs, which include the ancestors of all four-limbed vertebrates (i.e. tetrapods), began diverging from freshwater lobe-finned fish as their more robust and muscled pectoral and pelvic fins gradually evolved into forelimbs and hindlimbs, though they were not fully established for life on land until the Late Carboniferous. (Full article...)

Refresh with new selections below (purge)

Selected Devonian Article

From top to bottom and left to right, examples of sarcopterygians: Guiyu oneiros, West Indian Ocean coelacanth, Australian lungfish and the tetrapodomorph Panderichthys rhombolepis.

Sarcopterygii (/ˌsɑːrkɒptəˈrɪdʒi.aɪ/; from Ancient Greek σάρξ (sárx) 'flesh' and πτέρυξ (ptérux) 'wing, fin') is a clade (traditionally a class or subclass) of vertebrate animals which includes a group of bony fishes and all four legged land animals, including humans. The common name for this clade is lobe-finned fish.

Lobe-finned fish have muscular limb buds (lobes) within their fins, which are supported by appendicular skeletons. This is in contrast to the other clade of bony fishes, the Actinopterygii, which have only skin-covered bony spines supporting the fins.

Sarcopterygii emerged in the Silurian and early Devonian periods consisting entirely of aquatic species, but today the vast majority of its species are land animals called tetrapods. This mostly terrestrial clade of vertebrates are now recognized as having evolved from sarcopterygian ancestors and are most closely related to lungfishes. The lobed fins evolved into limbs, and foregut diverticulum eventually evolved into air-breathing lungs. These changes made it possible for tetrapods to explore and eventually permeate terrestrial ecosystems. While it is technically correct to include tetrapod species with Sarcopterygii, the phrase "lobe-finned fish" normally refers to the aquatic species that are not tetrapods. (Full article...)

List of selected Devonian articles

Selected Devonian land plant article

Archaeopteris fossil leaves

The progymnosperms are an extinct group of woody, spore-bearing plants that is presumed to have evolved from the trimerophytes, and eventually gave rise to the spermatophytes, ancestral to both gymnosperms and angiosperms (flowering plants). They have been treated formally at the rank of division Progymnospermophyta or class Progymnospermopsida (as opposite). The stratigraphically oldest known examples belong to the Middle Devonian order the Aneurophytales, with forms such as Protopteridium, in which the vegetative organs consisted of relatively loose clusters of axes. Tetraxylopteris is another example of a genus lacking leaves. In more advanced aneurophytaleans such as Aneurophyton these vegetative organs started to look rather more like fronds, and eventually during Late Devonian times the aneurophytaleans are presumed to have given rise to the pteridosperm order, the Lyginopteridales. In Late Devonian times, another group of progymnosperms gave rise to the first really large trees known as Archaeopteris. The latest surviving group of progymnosperms is the Noeggerathiales, which persisted until the end of the Permian.

Other characteristics:

Vascular cambium with unlimited growth potential is present as well as xylem and phloem.
Ancestors of the earliest seed plants as well as the first true trees.

Strong monopodial growth is exhibited. (Full article...)

List of selected Devonian articles

Selected Devonian formation

The Grey Downtonian facies occurs in the Downton Castle Sandstone Group of the British Old Red Sandstone, and more or less straddles the Devonian-Silurian boundary. The Ludlow Bone Bed and Temeside Shales are sometimes also included in the Grey Downtonian, which is also referred to as the Temeside group, part of the Downton Series. It is intermediate between the marine flagstones beneath it and the terrestrial deposits above it. The beds were deposited in a marine environment, with some material being washed in from the nearby land. (Full article...)

List of selected Devonian formation articles

Selected Devonian fish article

Fossil of Bothriolepis panderi, an antiarch placoderm showing its caliper-like pectoral fins

Placoderms (from Ancient Greek πλάξ [plax, plakos] 'plate' and δέρμα [derma] 'skin') are vertebrate animals of the class Placodermi, an extinct group of prehistoric fish known from Paleozoic fossils during the Silurian and the Devonian periods. While their endoskeletons are mainly cartilaginous, their head and thorax were covered by articulated armoured plates (hence the name), and the rest of the body was scaled or naked depending on the species.

Placoderms were among the first jawed fish (their jaws likely evolved from the first pair of gill arches), as well as the first vertebrates to have true teeth. They were also the first fish clade to develop pelvic fins, the second set of paired fins and the homologous precursor to hindlimbs in tetrapods. 380-million-year-old fossils of three other genera, Incisoscutum, Materpiscis and Austroptyctodus, represent the oldest known examples of live birth.

Placoderms are thought to be paraphyletic, consisting of several distinct outgroups or sister taxa to all living jawed vertebrates, which originated among their ranks. In contrast, one 2016 analysis concluded that Placodermi is likely monophyletic. (Full article...)

List of selected Devonian fish articles