| 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 Late Triassic is the third and last epoch of the Triassic period, corresponding to the Upper Triassic series of the Triassic system in stratigraphy. It began after the Ladinian age of the Middle Triassic at ~237 Ma (millions ago) and lasted until the Hettangian age of the Early Jurassic at 201.4 ± 0.2 Ma. The earliest unquestionable pterosaurs and dinosaurs are khown from this series. Perhaps the first true mammals appeared during this epoch. At the Late Triassic-Early Jurassic boundary, the T-J mass extinction occurred.
Definition[]
The GSSP of the Upper Triassic and the Carnian stage was ratified in 2008. The lower boundary is defined in 45 m above the base of San Cassiano Formation in Prati di Stuores, Italy, and related to the first appearance datum (FAD) of the ammonoid Daxatina canadensis. There are also the magnetic polarity zone S2n, the maximum flooding surface of Sequence Lad 3 and the FAD of the conodont "Paragondolella" polygnathiformis noah near this level.[2]
Subdivisions[]
The Upper Triassic divided into three stages: Carnian, Norian and Rhaetian. In geochronology, all of them correspond to the ages of the same names.
Paleogeography[]
During the Late Triassic, the supercontinent Pangea still existed. There is a possibility that at this time there was the largest land area for the entire Mesozoic era or even the Phanerozoic eon.
Late Triassic life[]
Pterosaurs and dinosaurs appeared in the Late Triassic. However, they did not become the dominant groups until the Jurassic period, although several dinosaurs (like Plateosaurus) reached large sizes already in this epoch. The first dinosaurs probably appeared in the area of modern South America. The earliest dinosaurs like Staurikosaurus, Panphagia, Eoraptor and Buriolestes are known from the Late Triassic of Brazil and Argentina. The oldest pterosaurs are known from Texas. Another important group, crocodylomorphs, also appeared in the Late Triassic and become more diverse later. The first true mammals also probably appeared at this time, although it is a question of whether Triassic cynodonts can be considered mammals. The oldest fossils of undisputed turtles (Odontochelys, Proterochersis and Proganochelys) are known from the Upper Triassic, but the question of whether the first turtles could have appeared before the Late Triassic also remains debatable.
The Late Triassic is the last epoch when the huge non-mammalian therapsids existed. The last dicynodonts like Placerias or Ischigualastia reached the mass of the modern rhinos. Lisowicia was even larger, similar to modern elephants with the mass estimating at 5–7 tons. These were slow animals with powerful beaks and fangs, with which they snacked on solid plant food.
Ichthyosaurs reached their peak at this time. The largest genera, similar in size to baleen whales, are assigned to the Shastasauridae family. Such ichthyosaurs as the Late Triassic Shonisaurus, Shastasaurus and Ichthyotitan were likely the largest marine animals of the Mesozoic. It is not entirely clear what their diet was and how they hunted.
Finally, the Late Triassic is also a golden time for non-crocodile pseudosuchians. Many of these animals occupied ecological niches that were later occupied by dinosaurs, and several Late Triassic pseudosuchians even looked like the dinosaurs. Shuvosaurids resembled ornithomimosaurians so much that at one time they were considered their representatives. Ornithosuchus and other large carnivorous psedosuchians looked like the early tetanuran theropods, although they had shorter legs and, as a result, moved more slowly. Aetosaurs were four-legged, armored herbivores, strongly reminiscent of later ankylosaurs. Despite their external resemblance to dinosaurs, all of these animals are pseudosuchians and their closest living relatives are crocodiles.
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.