| System (period) | Series (epoch) | Stage (age) | Lower boundary, Ma | |
|---|---|---|---|---|
| Jurassic | Lower | Hettangian | 201.4±0.2 | |
| Triassic | Upper (Late) | Rhaetian | ~208.5 | |
| Norian | ~227 | |||
| Carnian |  ~237
| |||
| Middle | Ladinian | ~242
| ||
| Anisian | 247.2 | |||
| Lower (Early) | Olenekian | 251.2 | ||
| Induan | 251.902±0.024
| |||
| Permian | Lopingian | Changhsingian | older | |
| Subdivisions and "golden spikes" according to IUGS as of September 2023[1] | ||||
The Middle Triassic is a second epoch of the Triassic period, corresponding to the Middle Triassic series of the Triassic system in stratigraphy. It began after the Olenekian age of the Early Triassic at 247.2 Ma (millions ago) and lasted until the Carnian age of the Late Triassic at ~237 MA. It is characterized by the noticeable increase in the diversity of archosaurs, which began to displace temnospondyls, therapsids and non-archosaur reptiles in the continental zone.
Definition[]
As of 2024, there is still no GSSP for Middle Triassic series and the Anisian stage. The candidates are the section at Desli Caira in Romania, sections in Guizhou Province of China and South Primorye, Russia. The First Appearing Datum (FAD) of the conodont Chiosella timorensis is suggested as the marker of the lower boundary of this series.[2]
Subdivisions[]
The Middle Triassic series divided into two stages, Anisian and Ladinian. In geochronology, both correspond to the ages of the same names.
Paleogeography[]
The supercontinent Pangea still extended from one pole to the other. However, in the Middle Triassic, the climate in the northern hemisphere became wetter with the formation of an extended gulf between Africa and Europe. Formed from parts of what is now South Asia, the Cimmerian ridge gradually moved north, dividing the Tethys Ocean into northern and southern parts.[3]
Middle Triassic life[]
The last therocephalians are known from the Middle Triassic. The most recent of them are likely Nothogomphodon from the Anisian of China and Microgomphodon from the Middle Triassic of Namibia. With the extinction of therocephalians, cynodonts and dicynodonts remained the only branches of synapsids for the rest of the Triassic.
Ichthyosaurs continued to flourish in the seas, many of which acquired a body shape similar to fish. Sauropterygians, another group of marine reptiles, also became more and more numerous. Nothosaurs reached the large sizes. Nothosaurus giganteus with the length of up to 7 m was the largest Triassic sauropterygian known to date[4]. The first placodonts like Psephosaurus, Psephosauriscus and Psephoderma appeared in the Middle Triassic. Pappochelys, a possible relative of turtles, existed in this epoch.
The first undoubted phytosaurs are known from the Middle Triassic. Diandongosuchus was among the earliest members of this group. Very similar to crocodiles, phytosaurs quickly replaced amphibians, occupying the niche of ambush aquatic predators.
At this time, many small, fast-running archosaurs, close to the first dinosaurs, already existed. Lewisuchus lived in what iI now Argentina where early dinosaurs later appeared. In the Anisian strata of Tanzania, Nyasasaurus was found. This animal is regarded by some researchers as the first dinosaur, although it may be a non-dinosaur avemetatarsalian.
References[]
- ↑ "Latest version of international chronostratigraphic chart". International Commission on Stratigraphy. https://stratigraphy.org/chart#latest-version.
- ↑ "GSSP Table - Mesozoic Era". https://timescalefoundation.org/gssp/index.php?parentid=35.
- ↑ "The Middle Triassic Epoch of the Triassic Period". http://palaeos.com/mesozoic/triassic/midtrias.html#:~:text=By%20the%20Middle%20Triassic%2C%20a,to%20the%20south%20of%20Eurasia..
- ↑ Liu, Jun (2014). "A gigantic nothosaur (Reptilia: Sauropterygia) from the Middle Triassic of SW China and its implications for the Triassic biotic recovery". Scientific Reports. 4: 7142. Bibcode:2014NatSR...4E7142L. doi:10.1038/srep0714