| System (period) | Series | Stage (age) | Lower boundary, Ma | |
|---|---|---|---|---|
| Permian | Cisuralian | Asselian | 298.9±0.15 | |
| Carboniferous | Pennsylvanian | Upper | Gzhelian | 303.7±0.1 |
| Kasimovian | 307.0±0.1 | |||
| Middle | Moscovian | 315.2±0.2 | ||
| Lower | Bashkirian |  323.2±0.4
| ||
| Mississippian | Upper | Serpukhovian | 330.9±0.2 | |
| Middle | Visean | 346.7±0.4
| ||
| Lower | Tournaisian | 358.9±0.4
| ||
| Devonian | Upper | Famennian | older | |
| Subdivisions and "golden spikes" according to IUGS as of September 2023[1] | ||||
The Bashkirian is a lower stage of the Pennsylvanian subsystem of the Carboniferous system, corresponding to the Bashkirian age of the Pennsylvanian part of the Carboniferous period. It lasted from approximately 323.2 Ma to around 315.2 Ma (million years ago). It is preceded by the Serpukhovian age of the Mississippian and is followed by the Moscovian age of the Pennsylvanian. The earliest eugeneodontiforms, xenacanthiforms, members of several arachnid groups, sauropsids and synapsids are known from this stage.
Definition[]
The GSSP of the Bashkirian stage and the whole Pennsylvanian subsystem was ratified in 1996. The lower boundary is fixed in the lower Bird Spring Formation in Arrow Canyon, Nevada, USA, and related to the first appearance of the conodont species Declinognathodus noduliferus.[2]
Bashkirian life[]
Ameura fossil
Echinoderms continued to flourish in the seas. Fossils of crinoids (platycrinitids, Pentaridica-like and Cyclocaudex-like specimens) have even been found in Antarctica, which at that time was covered in ice as well as the entire southern part of Pangea. Various stenolaemates (Rectifenestella, Australopolypora, Australofenestella), brachiopods (Streptorhynchus, Crurithyris), bivalves (Anthraconeilo, Limipecten, Streblopteria, Cypricardinia) and nautiloid cephalopods (Sueroceras) also lived in the Antarctic seas. Among ammonites, goniatitids (Syngastrioceras, Yakutoceras, Paraschartymites, Mezorulganites) have reached large numbers. A variety of arthropods still lived in the seas, although they were increasingly losing out in competition to fish. The number of trilobites remained small, and their fossils of this age are extremely rare, even if we consider those families known from later deposits. Griffithides, a phillipsiid trilobite of the last order, Proetida, is known from the Bashkirian of Nevada and California. Ditomopyge, Sevillia, and Ameura have been found in coastal sediments of Pottsville Formation in Ohio. Ostracodes, small shelled arthropods, were abundant in the seas. Bashkirian genera include Monoceratina, Healdia, Bythocypris, Cavellina, Paraparchites, and Amphissites. Eurypterids remained few in number. Many of them, such as Mycterops from Belgium, lived in continental bodies of water.
Sphenacanthus
Conodonts remained the most abundant group of marine chordates, and their fossils from this age are used in stratigraphy. Bashkirian genera include Adetognathus, Idiognathodus, Neognathodus, Polygnathus and Streptognathodus. Cartilaginous fish (chondrichthyans) were apparently the apex predators of that time. Eugeneodontiforms, unusual fishes with specific dentitions, appeared during this age. Edestus, the oldest member, is known from the Bashkirian strata of the United Kingdom and Oklahoma, USA. Xenacanthiform chondrichthyans also appeared during Bashkirian. Equipped with leaf-shaped fins and spines at the back of their heads, these fishes inhabited the seas and fresh waters, where they lived for more than a hundred million years. The oldest species, Pleuracanthus laevissimus and P. cylindricus, are known from Newsham, England. Other chondrichthyans of the time include protacrodontids (Protacrodus), symmoriiforms (Stethacanthus), sphenacanthids (Sphenacanthus), ctenacanthiforms (Cladodus, Heslerodus) and cochliodontiforms (Pleurodus, Paecilodus). Various bony fishes including palaeonisciforms (Platysomus, Rhadinichthys, Gyrolepis), eurynotiforms (Chirodus), rhizodontiforms (Strepsodus) and coelacanthimorphs (Coelacanthus) swam in the Bashkirian seas.
A model of Namurotypus
Life was in full swing in the vast swampy equatorial forests. Some arthropods that lived there reached gigantic sizes. Arthropleura, a myriapod, grew to more than 2 m in length. The oldest thelyphonids (Geralinura, Parageralinura), spiders (Protolycosa), and tickspiders (Curculioides) are known from this age. Various xiphosurans (Valloisella, Prestwichianella, Belinurus, Pringlia) and malacostracans (Palaeocaris, Pleurocaris, Anthracaris, Pygocephalus) lived in water, and their relatives, insects, have spread widely across land. Bashkiria is the lowest stage in which the diversity of insects can be traced. A possible reason is the appearance of wings and adaptation to flight. Having become the first flying animals, insects quickly spread throughout the forests and, apparently, beyond them. Erasipterid (Zessinella, Erasipteroides), meganisopteran (Namurotypus), diaphanopterodean (Namurodiapha), megasecopteran (Sylvohymen) and palaeodictyopteran (Patteiskya, Lithomantis, Homoioptera, Dictyoneura) insects have been found in Hagen-Vorhalle quarry in Germany.
Pholiderpeton
In addition to arthropods, many semi-aquatic tetrapods lived in the swamps. Despite the fact that many of them moved well on land, they needed the proximity of water to reproduce. Various temnospondyls (Dendrerpeton, Procochleosaurus), microsaurs (Lepterpeton, Archerpeton), baphetids (Loxomma, Megalocephalus) and nectrideans (Urocordylus, Batrachiderpeton, Keraterpeton) lived in Bashkirian swamps. Some amphibians reached huge sizes, such as Pholiderpeton with a length of over 4 m. Despite the accepted name, not all of these animals are the ancestors of modern frogs, newts and caecilians. Some prehistoric "amphibians", however, acquired external resemblance to them. Phlegethontia has lost its hind limbs, and Ophiderpeton has lost both its hind and forelimbs, becoming caecilian-like. The most important event of this age was the appearance of terrestrial tetrapods, which laid eggs immediately on land, in a safe place. The oldest sauropsids (Hylonomus) and synapsids (Asaphestera, Protoclepsydrops) are known from the Bashkirian Joggins Formation of Nova Scotia, Canada. Millions of years later, reptiles and birds subsequently evolved from sauropsids, while mammals are descendants of early synapsids.
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.