| System (period) | Series (epoch) | Stage (age) | Lower boundary, Ma | ||
|---|---|---|---|---|---|
| Carboniferous | Mis. | Lower | Tournaisian | 358.9±0.4 | |
| Devonian | Upper (Late) | Famennian |  372.2±1.6
| ||
| Frasnian | 382.7±1.6
| ||||
| Middle | Givetian | 387.7±0.8
| |||
| Eifelian | 393.3±1.2
| ||||
| Lower (Early) | Emsian | 407.6±2.6
| |||
| Pragian | 410.8±2.8
| ||||
| Lochkovian | 419.2±3.2
| ||||
| Silurian | Pridoli | older | |||
| Subdivisions and "golden spikes" according to IUGS as of September 2023[1] | |||||
The Pragian is a second stage of the Lower Devonian series, corresponding to the Pragian age of the Early Devonian epoch. It lasted from approximately 410.8 Ma to around 407.6 Ma (million years ago). It is preceded by the Lochkovian and is followed by the Emsian. The earliest acariform mites, springtails and undoubted euthycarcinoids are known from this stage.
It was named after the Czech city of Prague by Chlupač I. in 1958.
Definition[]
The GSSP of the Pragian stage was ratified in 1989. The lower boundary is fixed at the base of Bed 12 in Velká Chuchle Quarry, Prague, Czech Republic, and related to the first appearance of the conodonts Eognathodus sulcatus sulcatus and Latericriodus steinachensis Morph beta.[2]
Pragian life[]
Life flourished in shallow waters and in the open ocean. In the coastal zone, reefs consisting of Favosites, Striatopora and other coral polyps continued to form. A variety of brachiopods (Plicoplasia, Cyrtina, Discomyorthis, Uncinulus), bivalves (Leptodomus, Goniophora, Modiomorpha, Nuculites) and gastropods (Oriostoma, Omphalocirrus, Alaionema, Coelocaulus) lived on the seafloor. Cephalopods hunted in the water column, including early ammonites such as Mimagoniatites, Erbenoceras and Metabactrites. Ammonites had a strong, twisted shell that protected them from the claws and teeth of predators. Other cephalopods of the time include discosorids (Pseudendoplectoceras), orthocerids (Tibichoanoceras), dissidocerids (Temperoceras) and pseudorthocerids (Spyroceras, Cancellspyroceras).
Palaeocharinus rhyniensis
Rhyniognatha hirsti specimen
A variety of arthropods still lived in the seas. Trilobites, whose numbers were no longer as high as before, were predominantly benthic forms. Pregian trilobites include genera Reedops, Acastoides, Dalmanites, Phacops, Platyscutellum, Anchiopsis, Synphoroides, and Calymene. Chasmataspidids (Diploaspis) and eurypterids (Wiedopterus, Parahughmilleria, Acutiramus, Jaekelopterus) inhabited both coastal waters, rivers and lakes. Arachnids increased their numbers on land. Various scorpions (Waeringoscorpio), trigonotarbids (Spinocharinus, Archaeomartus, Palaeocteniza, Palaeocharinus), phalangiotarbids (Devonotarbus) and the earliest acariform mites (Protacarus, Pseudoprotacarus, Protospeleorchestes, Paraprotacarus) have been found in the Pragian strata. Euthycarcinoids, another group of arthropods, also appears in this stage. These animals, which had many limbs, could probably live both in water and on land. Little is known about their evolution. Some researchers believe that euthycarcinoids arose in the Cambrian or even Ediacaran, but Heterocrania, the oldest member, is known from the Pragian of Scotland. The first undoubted hexapods are also known from the Pragian. Rhyniella is the oldest known springtail, while the taxonomy of Leverhulmia is controversial. Rhyniognatha, another arthropod of the time, is interpreted by some authors as an ancient insect, although it may also be a centipede. Some researchers suggest that insects appeared long before this age and the Devonian period.
Wuttagoonaspis fletcheri
Porolepis
Vertebrates still lived in the water. The seas were inhabited by conodonts, somewhat similar to modern lampreys. Their sharp teeth, well preserved in fossil form, were well suited for butchering soft-bodied animals. Pragian conodonts include Icriodus, Belodella, Ozarkodina, Wurmiella, Panderodus, Caudicriodus and other genera. Numerous fish, including Chondrichthyes (Machaeracanthus, Striacanthus) and placoderms (Wuttagoonaspis, Mulgaspis) lived in both the seas and rivers. Porolepis, a dipnomorph, was closely related to the early tetrapodomorphs. Such fish could probably wait out droughts by burying themselves in the mud and consuming oxygen from the atmosphere.
References[]
- ↑ "Latest version of international chronostratigraphic chart". International Commission on Stratigraphy. https://stratigraphy.org/chart#latest-version.
- ↑ "GSSP Table - Paleozoic Era". https://timescalefoundation.org/gssp/index.php?parentid=77.