| 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 Tournaisian is a first stage of the Mississippian subsystem and the Carboniferous system, corresponding to the Tournaisian age of the Mississippian part of the Carboniferous period. It lasted from approximately 358.9 Ma to around 346.7 Ma (million years ago). It is preceded by the Famennian age of the Late Devonian and is followed by the Visean age of the Mississippian. This age began with the end-Devonian extinction that eliminated many groups of trilobites and armored fish that were abundant in the Devonian.
Definition[]
The GSSP of the Tournaisian stage was ratified in 1990. The lower boundary is fixed in the base of Bed 89 in Trench E' at La Serre, France, and approximately related to the first appearance of the conodont species Siphonodella sulcata.[2]
Tournaisian life[]
The extinctions of the Late Devonian caused severe damage to corals. The processes of reef formation slowed down greatly and remained so until the Mesozoic. Among trilobites, only members of the order Proetida survived. Pudoproetus, Thigriffides, Phillibole and Australosutura are known from the Tournaisian strata of the North America. Eurypterids survived extinction, but remained small in number. Cyrtoctenus, a hibbertopterid, was found in the Tournaisian deltaic sediments of Montgomery County, Virginia, USA. Ammonites also survived extinction. Eocanites, Paragattendorfia, Mimimitoceras, Nicimitoceras, and Zadelsdorfia lived in coastal waters in what is now Morocco.
Acanthodes
Cartilaginous fishes remained largely untouched by extinctions and continued to spread across the planet. Psammodus lived near the seabed. Long-bodied, eel-like Thrinacodus and Listracanthus probably hunted by attacking from the seaweed thickets. Homalacanthus, Acanthodes and Carycinacanthus lived in coastal zone. Marine bony fishes of the Tournaisian include palaeonisciforms (Grassator, Cycloptychius, Holurus), gyrolepidotids (Gyrolepidotus), elonichthyiforms (Elonichthys) and rhizodontiforms (Rhizodus). Non-tetrapodomorph lobe-finned fishes like Greiserolepis and Medoevia lived in seas and lagoons. Semiaquatic tetrapodomorphs from the Tournaisian were not discovered for a long time, and their absence from the fossil record was called the "Romer's gap". However, since 2015, several stem-tetrapods and true tetrapods of the families Acanthostegidae, Tulerpetontidae, Crassigyrinidae and Whatcheeriidae were found in the Tournaisian sediments of Horton Bluff Formation in Nova Scotia, Canada. All of them as well as Avonichthys, a ray-finned fish, lived in river deltas.
A variety of centipedes and arachnids lived on land. It is assumed that insects also reached a certain diversity, but their fossils of this age are unknown.
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.