| 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 Induan is the lowermost stage of the Lower Triassic series, Triassic system and Mesozoic erathem, corresponding to the Induan age of the Early Triassic epoch of the Triassic period of the Mesozoic era. It lasted from approximately 251.902 Ma (million years ago) to around 251.2 Ma. It is preceded by the Changhsingian age of the Lopingian epoch and is followed by the Olenekian age of the Early Triassic. With a duration of around 702,000 years, Induan is the shortest non-Quaternary age of the Phanerozoic eon. The beginning of the Induan corresponds to the Permian-Triassic extinction event, the most severe mass extinction in Earth's history. The earliest perleidiforms, chigutisaurids and lepidosauromorphs are known from this stage.
It includes Griesbachian and Dienerian substages.
Definition[]
Teeth of Hindeodus parvus
The GSSP of the Induan stage, Lower Triassic series, Triassic system and the whole Mesozoic erathem was ratified in 2001. The lower boundary is fixed in the Kuhjoch section in the Meishan D Section, Zhejiang Province, China, and related to the first appearance of the conodont species Hindeodus parvus.[2]
Climate[]
After the eruptions of the Siberian Traps and numerous fires, the climate became much hotter and dryer. Deserts continued to expand from the equatorial and tropical regions of the single continent of Pangea. Anoxic conditions persisted in the seas. This ecological situation prevented the rapid recovering of the biota, and some of those groups that survived the extinction remained small in number and soon died out completely.
Induan life[]
The Permian-Triassic extinction reduced the number of marine species by more than 90%. Trilobites, eurypterids, and several groups of ammonites became completely extinct in the seas. On land, various groups of insects, amphibians, sauropsids and synapsids died out, and new species began to gradually settle across the planet after the end of the disaster.
Ophiceras medium (sakuntala) fossil
Stenolaemates, important reef builders, were represented by Pseudobatostomella, Arcticopora, and Paralioclema. Various brachiopoda (Lingularia, Fusichonetes, Acosarina, Paracrurithyris), gastropods (Holopella, Coelostylina, Warthia, Neritaria) and bivalves (Unionites, Claraia, Promyalina, Neoschizodus) lived in shallow sea waters. Ammonite diversity declined markedly, but ceratitids survived. Their numerous representatives, including Gyronites, Ophiceras, Discophiceras, Danubites, and Ussuridiscus are known from Induan deposits. Nautilids, close relatives of ammonites, also survived. Gyronautilus lived in the seas by east of Pangea. The expansion of deserts did not prevent horseshoe crabs from surviving in fresh water bodies. Tasmaniolimulus inhabited lakes in what is now Tasmania. Ostracodes (Hollinella, Carinaknightina, Truncobairdia, Bairdiacypris) remained a large group of aquatic arthropods.
Saurichthys fossil
Pteronisculus fossil
Among chordates, conodonts remained a large group, making them important for stratigraphy. Induan genera include Ellisonia, Eurygnathodus, Isarcicella, Neospathodus, and Hadrodontina. Hybodontiform shark-like chondrichthyans (Omanoselache, Polyfaciodus, Acrodus, Lissodus) have spread widely in the ocean and fresh waters. Some of them are found in lake sediments that formed far from the sea. Eugeneodontiforms also survived, but in small numbers. One of them, Helicampodus, is known from the Induan strata of India and China. Among osteichthyans (bony fishes), a new order, Perleidiformes, appeared. Oldest members include Perleidus, Colobodus, and Teffichthys. Saurichthys, another osteichthyan, was one of those genera that survived the mass extinction. Other osteichthyans of the time include acipenseriforms (Errolichthys), palaeonisciforms (Gyrolepis, Pteronisculus, Birgeria, Pteronisculus), ptycholepiforms (Boreosomus, Ardoreosomus), parasemionotiforms (Parasemionotus, Watsonulus, Candelarialepis, Stensionotus), coelacanthiforms (Whiteia, Coelacanthus), pholidopleuriforms (Australosomus) and others.
Wetlugasaurus
Benthosuchus
Axitectum
Dromotectum
Temnospondyls survived extinction in several continental bodies of water in high latitudes. Wetlugasaurus, Selenocara, Samarabatrachus, Luzocephalus, Benthosuchus, Tupilakosaurus and other temnospondyls inhabited rivers and lakes of northern Pangea. Similar to crocodiles, these amphibians probably led a similar lifestyle, ambushing animals that came to drink. Aphaneramma, a trematosaurid, probably lived in the seas. Keratobrachyops, probably the oldest known chigutisaurid temnospondyl, has been discovered in Induan Arcadia Formation of Queensland, Australia. Chroniosuchians (Axitectum, Dromotectum) also survived into Triassic. Having thicker skin, these amphibious predators could spend more time on land.
Galesaurus
Even more noticeable changes occurred among amniotes. Apart from dicynodonts, therocephalians and cynodonts, there were no other synapsids left on the planet. For a short time, one genus of dicynodonts, Lystrosaurus, became the most numerous land vertebrate. During Induan, these tusked and beaked herbivores spread across the entire eastern coast of Pangea, including territories of South Africa, Russia and China. The reason for such a successful restoration of Lystrosaurus numbers remains a mystery. Moschorhinus, a therocephalian, also survived and probably remained the only therapsid predator that could hunt Lystrosaurus. Cynodonts like Galesaurus survived due to their small size. Having adapted to the new climate and hiding from large predators, after millions of years they evolved into mammals.
Chasmatosuchus
Fossilized skulls of Kudnu
The hot climate turned out to be ideal for sauropsids, although their diversity also decreased markedly. Only one group of parareptiles, procolophonoids, survived. Similar to lizards, owenettids (Saurodektes) and procolophonids (Phaanthosaurus, Eomurruna) were small animals and fed on plants or invertebrates. True reptiles have spread widely. Some of them, like Hovasaurus, have adapted to life in water. Large carnivores arose among archosauromorphs, the most successful group of land vertebrates for the next 186 million years. Such animals as Chasmatosuchus, Proterosuchus, Tasmaniosaurus, Kadimakara and probably Vonhuenia had long and slightly curved jaws, suitable for capturing large prey. Protorosaurids like Microcnemus had long necks and resembled lizards, although they are close relatives of crocodiles, dinosaurs and pterosaurs, which would appear among archosauromorphs later. Lepidosauromorphs, the real ancestors of lizards, snakes and tuataras, already existed in this age, although their earliest members are not well known. Possible Induan genera include Kudnu, Blomosaurus, and Santaisaurus.
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.