| 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 Rhaetian is, in geochronology, the latest age of Triassic period or, in chronostratigraphy, the uppermost stage of the Triassic system. It lasted from ~208.5 to 201.4 ± 0.2 mya. It was preceded by the Norian and succeeded the Hettangian (the lower stage or the earliest age of the Jurassic). At the Rhaetian-Hettangian boundary, one of the major extinctions occurred. The last perleidiforms, dicynodonts, rauisuchids, phytosaurs and many other animal groups are known from this stage.
Unlike other Triassic stages, Rhaetian does not include any substages.
Definition[]
As of 2024, there is still no GSSP defining the base of this stage. The candidates are Pizzo Mondello on Sicily, Italy, and Steinbergkogel in Austria. The First Appearing Datum (FAD) of the conodont species Misikella posthernsteini is suggested as the marker of the lower boundary of this stage.[2]
Rhaetian life[]
Semionotiform (Sargodon) and palaeonisciform fish (Gyrolepis, Birgeria) remained numerous and they were prey for coastal cartilaginous fish such as Lissodus, Pseudodalatias and Synechodus. The last placodonts known from Rhaetian deposits. Some of them, like Psephoderma or Macroplacus, lived in the seas, while others, like Chelyoposuchus, on floodplains, where they coexisted with temnospondyls. Nothosaurs also disappear from the geological record after the Rhaetian. One of the latest nothosaurs is Simosaurus. The last parareptiles like Hypsognathus lived out their days in this age. Primitive turtles like Proganochelys and Proterochersis are known from the Rhaetian. The number of small mammaliaforms increased. Thomasia appeared in this age and survived in the next one, of the Jurassic period.
A small theropod and Lisowicia
By the end of the Triassic, several giant species appeared in various animal groups. Lisowicia, one of the largest dicynodonts, existed from the Norian to the end of the Rhaetian. Simultaneously with it, but in another part of the continent, Scalenodontoides, the largest non-mammalian cynodont, existed. Ichthyotitan, the huge ichthyosaur, was discovered in the Rhaetian bone bed of Westbury Formation in the United Kingdom.
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.