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 60.3 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.

Fishes, 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

Diagram showing evolution of Bactritida to Ammonoidea

The Bactritida are a small order of more or less straight-shelled (orthoconic) cephalopods that first appeared during the Emsian stage of the Devonian period (407 million years ago) with questionable origins in the Pragian stage before 409 million years ago, and persisted until the Carnian pluvial event in the upper middle Carnian stage of the Triassic period (231 million years ago). They are considered ancestors of the ammonoids, as well as of the coleoids (octopus, squid, cuttlefish, and the extinct belemnites).

Bactritids are distinguished from the more primitive nautiloids by the small size and globular shape of the protoconch, the so-called embryonic shell. Nautiloids have relatively large embryonic shells, and living species lay a few large eggs. In contrast, bactritids and ammonoids produced large numbers of small eggs, each housing a small embryonic shell. (Full article...)

List of selected Devonian articles
Sarcopterygii Trilobites Marcellus Formation Late Devonian extinction Acadian Orogeny List of Early Devonian land plants Dunkleosteus

Selected Devonian land plant article

A pteridophyte is a vascular plant (with xylem and phloem) that reproduces by means of spores. Because pteridophytes produce neither flowers nor seeds, they are sometimes referred to as "cryptogams", meaning that their means of reproduction is hidden. They are also the ancestors of the plants we see today.

Ferns, horsetails (often treated as ferns), and lycophytes (clubmosses, spikemosses, and quillworts) are all pteridophytes. However, they do not form a monophyletic group because ferns (and horsetails) are more closely related to seed plants than to lycophytes. "Pteridophyta" is thus no longer a widely accepted taxon, but the term pteridophyte remains in common parlance, as do pteridology and pteridologist as a science and its practitioner, for example by the International Association of Pteridologists and the Pteridophyte Phylogeny Group. (Full article...)

List of selected Devonian articles
Sigillaria Pteridospermatophyta Lycophyte Equisetidae Progymnosperm Rhyniophyte Trimerophytopsida Lycopodiopsida

Selected Devonian formation

The Tully Formation is a geologic unit in the Appalachian Basin. The Tully was deposited as a carbonate rich mud, in a shallow sea at the end of the Middle Devonian. Outcrops for the Tully are found in New York State and Pennsylvania. It is also found subsurface in western Maryland and northern West Virginia. A number of fossil remains from marine organisms may be found in Tully outcrops. (Full article...)

List of selected Devonian formation articles
Hamilton Group Tioga Bentonites Windom shale Rhinestreet Formation Oriskany Formation Bakken formation Traverse Group New Albany Shale Old Red Sandstone Grey Downtonian

Selected Devonian fish article

C. dentata

Ctenaspis (Ctenaspis kaieri) is an extinct genus of heterostracan cyathaspid agnathans from the early Devonian of Canada, Norway and Russia 416.0 to 412.3 million years ago. Species of Ctenaspis are typically 10 to 18 cm long with the max length being 40 cm long. The genus contains only one known species, namely Ctenaspis kaieri.

C. kaieri has no adorbital opening and only two dorsal and ventral plates . The dorsal plate is fused with branchials and the plates notably thin. C. kiaeri has its branchial openings located at the posterior edge of armour. The dorsal shield is flat. (Full article...)

List of selected Devonian fish articles
Brochoadmones Cheirolepis Holoptychius Hyneria Lepidaspis Scaumenacia Tinirau clackae Placoderm Diplocercides Dipterus Elpistostegalia Gooloogongia Ventastega Tristichopteridae Phoebodus Stethacanthidae Xenacanthus

Selected Devonian invertebrate

Top view of a stromatoporoid with prominent mamelons. From the Columbus Limestone (Middle Devonian) of Ohio.

Stromatoporoidea is an extinct clade of sea sponges common in the fossil record from the Middle Ordovician to the Late Devonian. They can be characterized by their densely layered calcite skeletons lacking spicules. Stromatoporoids were among the most abundant and important reef-builders of their time, living close together in flat biostromes or elevated bioherms on soft tropical carbonate platforms.

Externally, some species have raised bumps (mamelons) and star-shaped crevices (astrorhizae), which together help vent exhalant water away from the living surface. Internally, stromatoporoids have a mesh-like skeletal system combining extensive horizontal layers (laminae), vertical rods (pillars), and boxy spaces (galleries), along with other features. The most common growth forms range from laminar (flattened) to domical (dome-shaped). Spheroidal, finger-like, or tree-like species also occur, though they are rare in most environments.

Stromatoporoids competed and coexisted with other reef-builders such as tabulate and rugose corals. Some stromatoporoid species are useful as environmental proxies, since their form and distribution can help approximate the depositional environment of sedimentary strata. They hosted a diverse fauna of encrusting symbionts both within and outside their skeletons. Some studies have argued that stromatoporoids were mixotrophs (engaged in a mutualistic relationship with photosynthetic algae), similar to modern scleractinian corals. Though this hypothesis is plausible, circumstantial evidence is inconclusive. (Full article...)