| 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 Olenekian is an upper stage of the Lower Triassic series, corresponding to the Olenekian age of the Early Triassic epoch. It lasted from 251.2 MA (million years ago) to 247.2 Ma. It was preceded by the Induan age of the Early Triassic and is followed by the Anisian age of the Middle Triassic. The earliest cornudinine conodonts, thalattosaurs, sauropterygians, erythrosuchids, rauisuchids, tanystropheids, kuehneosaurids and cynognathians as well as the last eugeneodontiforms, listracanthids and lystrosaurids are known from this stage.
It includes Smithian and Spathian substages.
Definition[]
There is still no GSSP for Olenekian. The candidates are Mud (Muth) village in Spiti valley, India, and Chaohu, China. The First Appearing Datum (FAD) of conodont Novispathodus waageni within a prominent positive Carbon-13 peak is suggested as the marker of the lower boundary of this stage. The lowest occurrence of Flemingites and Euflemingites ammonite genera can also be used for correlation.[2]
Olenekian life[]
1.5 million years after the Permian-Triassic mass extinction, cosystems continued to recover.[3] New groups, which later became diverse, arose during this age, but some Paleozoic organisms were never able to regain their former greatness.
Trematoceras boreale and Trematoceras subcampanile fossil specimens
Fossil spike of Palaeobates
Glikmanius
Caseodus
Paredestus head
Brachiopods and bivalves settled in the shallow coastal waters of Pangea. Cephalopods became the most diverse group of marine mollusks and remained so until the end of the Mesozoic. Various ammonoid (Popovites, Svalbardiceras, Parasibirites, Keyserlingites), nautilid (Syringoceras, Anoploceras, Enoploceras, Phaedrysmocheilus) and pseudorthocerid (Paratrematoceras, Trematoceras) cephalopods hunted in Olenekian seas. Another group of cephalopods, Belemnitida, has been constantly present in geological deposits from this stage to the very top of the Cretaceous. Similar to squids, belemnites had a hard, cone-shaped internal core, which probably served as ballast. Tohokubelus, a sinobelemnitid, was found in the Olenekian strata of Osawa Formation in Japan. Numerous conodonts still lived in the seas, and their fossils from this age are used in stratigraphy along with ammonites. Olenekian conodonts include Gladigondolella, Triassospathodus, Chiosella, and Novispathodus. The oldest members of the Cornudininae subfamily are known from this stage. These are Cornudina, Neostrachanognathus, Aduncodina and other genera. A variety of cartilaginous fishes lived in the seas and rivers, although the poor preservation of their skeletons (with the exception of teeth) sometimes makes it difficult to accurately identify the species and genus. Synechodontiform (Polyfaciodus, Safrodus, Nemacanthus), hybodontiform (Omanoselache, Palaeobates, Acrodus, Polyacrodus), ctenacanthiform (Pyknotylacanthus, Glikmanius), symmoriiform (Gunnellodus) and cochliodontiform (Deltodus) chondrichthyans are known from the Olenekian. Fossils of the latest listracanthids, cartilaginous fishes that appeared in the Tournaisian, are known from this stage. One of the latest species, Listracanthus pectenatus, was found in Sulphur Mountain Formation in Canada, alongside another chondrichthyan group that was close to extinction, Eugeneodontiformes. Caseodus, Fadenia, and Paredestus were likely the last of these fishes that had an unusual dental system and were related to modern chimaeras. The reason for their extinction is probably the emergence of new aquatic predators or the disappearance of the typical shelled animals on which they fed. Bony fish also lived in abundance in the seas and rivers. Perleidiforms (like Helmolepis) were a group that spread widely in the Triassic.
Thoosuchus
Trematotegmen skull
Diverse freshwater fishes became food for amphibians, some of which survived from a previous age. Temnospondyls (Wetlugasaurus, Benthosuchus, Yarengia, Vyborosaurus, Thoosuchus, Prothoosuchus, Trematotegmen, Inflectosaurus) and reptiliomorphs (Vyushkoviana, Dromotectum, Axitectum) were ambush predators, probably reminiscent of crocodiles in their lifestyle.
A variety of therapsids still lived on land at this time. Lystrosaurus were living out their last days. Having spread widely in the previous Induan age, they began to decline in numbers and eventually became completely extinct in Olenekian. With their disappearance, the family Lystrosauridae ceased to exist. Other dicynodonts of the time include Myosaurus and Putillosaurus, a member of the lagre family Kannemeyeriidae. Therocephalians still existed, but were already noticeably losing in competition to sauropsid predators. Silphedosuchus, an ericiolacertid therocephalian, is known from Petropavlovka Formation in Russia. Microgomphodon from the family Nothogomphodontidae was found in Beaufort Group of Burgersdorp Formation in South Africa. The variety of cynodonts has increased, and a new group, cynognathians, appeared. Beishanodon from China and Langbergia from South Africa were among the oldest members. Having spread even more widely in later ages, these dog-like predators eventually became extinct, leaving no descendants. Mammals are descended from other cynodonts, closely related to Thrinaxodon and Galesaurus which also existed during this time.
Phalarodon
Hanosaurus
Majiashanosaurus discocoracoidis cast
Pamelina skull
Tichvinskia
From this age the dawn of sauropsids begins. Many groups that later became widespread emerged. Proterosuchids (Chasmatosuchus) and first erythrosuchids (Garjainia) were large-headed animals, while rauisuchids (Scolotosuchus, Scythosuchus) could run quickly on their hind legs. These predators from the group of Archosauromorpha began to actively displace therapsids and eventually became the dominant terrestrial vertebrates. Several reptiles have evolved a number of specific traits. Ctenosauriscids like Ctenosauriscus and Bystrowisuchus had high dorsal sails, like some synapsids and amphibians of the Permian period. Tanystropheids (Augustaburiania) and some prolacertids (Vritramimosaurus) are characterized by long necks, with the help of which they probably caught small aquatic animals. Some reptiles have adapted to life in the seas. Thalattosaurs (Agkistrognathus, Paralonectes) had a streamlined body, but probably still retained the ability to move on land using their limbs. Ichthyopterygians, which also appeared by this time, had flippers and caudal fins and probably spent their entire lives in the sea. Such animals as Omphalosaurus, Grippia and Gulosaurus were close to ichthyosaurs, the most adapted to life in the ocean of all reptiles. Earliest ichthyosaurs include Phalarodon, Utatsusaurus, Pessopteryx, and Quasianosteosaurus. Sauropterygians, another group of marine reptiles, also arose around this time. Earliest genera include Tanaisosaurus, Hanosaurus, Majiashanosaurus, and Keichousaurus. Unlike thalattosaurs and ichthyopterygians, they retained many of the features of their land-dwelling ancestors and probably laid eggs on coasts. The origins of all these marine reptiles are still unclear, although sauropterygians are thought to have descended from the same ancestors as turtles. Kuehneosaurids, reptiles capable of gliding flight first appeared in Olenekian. Pamelina is their oldest known genus. Among parareptiles, only small, lizard-like members remained, such as Kapes, Orenburgia, and Tichvinskia from the family Procolophonidae.
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.
- ↑ C. Romano; T. Argyriou; L. Krumenacker (2019). "Chondrichthyan teeth from the Early Triassic Paris Biota (Bear Lake County, Idaho, USA)". Geobios 54: 63-70. DOI:10.1016/j.geobios.2019.04.001