Olenekian

The Olenekian stage was introduced into scientific literature by Russian stratigraphers in 1956.[9] The stage is named after Olenëk in Siberia. Before the subdivision in Olenekian and Induan became established, both stages formed the Scythian stage, which has since disappeared from the official timescale.

The base of the Olenekian is at the lowest occurrence of the ammonoids Hedenstroemia or Meekoceras gracilitatis, and of the conodont Neospathodus waageni. It is defined as ending near the lowest occurrences of genera Japonites, Paradanubites, and Paracrochordiceras; and of the conodont Chiosella timorensis. A GSSP (global reference profile for the base) has not been established as of December 2020.

The gymnosperm plant Voltzia heterophylla

Marine reptile Chaohusaurus

Life was still recovering from the severe end-Permian mass extinction. During the Olenekian, the flora changed from lycopod dominated (e.g. Pleuromeia) to gymnosperm and pteridophyte dominated.[10][11] These vegetation changes are due to global changes in temperature and precipitation. Conifers (gymnosperms) were the dominant plants during most of the Mesozoic. Among land vertebrates, the archosaurs - a group of diapsid reptiles encompassing crocodiles, pterosaurs, dinosaurs, and ultimately birds - first evolved from archosauriform ancestors during the Olenekian. This group includes ferocious predators like Erythrosuchus.

In the oceans, Microbial reefs were common during the Early Triassic, possibly due to lack of competition with metazoan reef builders as a result of the extinction.[12] However, transient metazoan reefs reoccurred during the Olenekian wherever permitted by environmental conditions.[13] Ammonoids and conodonts diversified, but both suffered losses during the Smithian-Spathian boundary extinction[14] at the end of the Smithian subage.

Ray-finned fishes largely remained unaffected by the Permian-Triassic extinction event.[15][16] Many genera show a cosmopolitan (worldwide) distribution during the Induan and Olenekian (e.g. Australosomus, Birgeria, Parasemionotidae, Pteronisculus, Ptycholepidae, Saurichthys). This is well exemplified in the Griesbachian (early Induan) aged fish assemblages of the Wordie Creek Formation (East Greenland), the Dienerian (late Induan) aged assemblages of the Sakamena Formation (Madagascar), Candelaria Formation (Nevada, United States), and Mikin Formation (Himachal Pradesh, India), and the Smithian aged assemblages of the Vikinghøgda Formation (Spitsbergen, Norway), Thaynes Formation (western United States), and Helongshan Formation (Anhui, China).

Marine temnospondyl amphibians, such as Aphaneramma or Wantzosaurus show wide geographic ranges during the Induan and Olenekian ages. Their fossils are found in Greenland, Spitsbergen, Pakistan and Madagascar.[17] The first marine reptiles appeared during the Olenekian.[17] Hupehsuchia, Ichthyopterygia and Sauropterygia are among the first marine reptiles to enter the scene (e.g. Cartorhynchus, Chaohusaurus, Utatsusaurus, Hupehsuchus, Grippia, Omphalosaurus, Corosaurus). Sauropterygians and ichthyosaurs ruled the oceans during the Mesozoic Era.

A major extinction event occurred during the Olenekian: the Smithian-Spathian boundary extinction.[18] This event was probably caused by late eruptions of the Siberian Traps and led to extinctions among several groups, especially nektonic and pelagic taxa such as ammonoids and conodonts. One of several exceptionally diverse Early Triassic assemblages, the Paris Biota[19] (from near Paris, southeast Idaho), was deposited in the wake of the Smithian-Spathian boundary extinction. It features at least 7 phyla and 20 distinct metazoan orders, including leptomitid protomonaxonid sponges (previously only known from the Paleozoic), thylacocephalans, crustaceans, nautiloids, ammonoids, coleoids, ophiuroids, crinoids, and vertebrates.[20]

The Olenekian ammonoid Hedenstroemia

• Gnathorhizids
• Trematosaurids
• Ichthyosauromorphs
• Sauropterygians
• Archosaurs
• Erythrosuchids
• Proterosuchids
• Crurotarsi
  • Rauisuchia

Cartilaginous fishes

Chondrichthyes of the Olenekian
Taxa	Presence	Location	Description	Images
Hybodus	Lopingian to Late Cretaceous	Svalbard	A hybodont elasmobranch	Hybodus Listracanthus
Listracanthus	Carboniferous to Early Triassic	Canada	A chondrichthyan with uncertain affinities, known primarily from their feather-like denticles.
Nemacanthus	Lopingian to Late Triassic	United States	A synechodontiform elasmobranch
Palaeobates	Triassic	Svalbard	A hybodont elasmobranch
Pyknotylacanthus	Early Triassic	United States

Ray-finned fishes

Actinopterygii of the Olenekian
Taxa	Presence	Location	Description	Images
Birgeria	Triassic	United States, Svalbard	A non-neopterygian	Birgeria Bobasatrania Saurichthys
Bobasatrania	Lopingian to Middle Triassic	Svalbard	A non-neopterygian
Boreosomus	Early Triassic	Greenland, Madagascar	A non-neopterygian
Helmolepis	Early Triassic	Svalbard	A platysiagid
Pteronisculus	Early Triassic to Middle Triassic	Svalbard	A non-neopterygian
Saurichthys	Triassic	United States, Svalbard, China	A non-neopterygian

Coelacanths

Actinistia of the Olenekian
Taxa	Presence	Location	Description	Images
Axelia	Early Triassic	Svalbard	A coelacanth	Rebellatrix
Mylacanthus	Early Triassic	Svalbard	A coelacanth
Rebellatrix	Early Triassic	Canada	A fork-tailed coelacanth
Sassenia	Early Triassic	Svalbard	A coelacanth
Scleracanthus	Early Triassic	Svalbard	A coelacanth
Wimania	Early Triassic	Svalbard	A coelacanth

Lungfishes

Dipnoi of the Olenekian
Taxa	Presence	Location	Description	Images
Ceratodus	Early Triassic to Eocene	Poland, Russia, Antarctica, Germany	A ceratodontid dipnoan, a close relative of the extant Australian lungfish Neoceratodus.	Ceratodus Gnathorhiza
Gnathorhiza	Permian to Early Triassic	Poland, Russia	A gnathorhizid dipnoan.
Namatozodia	Early Triassic	Australia	A small dipnoan, likely a gnathorhizid.
Ptychoceratodus Ptychoceratodus donensis ?Ptychoceratodus sp.	Early Triassic	P. donensis: Russia ?P. sp.: South Africa	A genus of derived ceratodontoid lungfish.

†Temnospondyls

Temnospondyli of the Olenekian
Taxa	Presence	Location	Description	Images
Angusaurus	Spathian	Russia	A trematosaurid stereospondyl amphibian	Aphaneramma Benthosuchus Parotosuchus nasutus Parotosuchus orenburgensis Sclerothorax Trematosaurus Wetlugasaurus
Aphaneramma	Early Triassic	Svalbard	A trematosaurid stereospondyl amphibian
Batrachosuchoides	Early Spathian	Poland; Russia	A brachyopid stereospondyl amphibian.
Benthosuchus	Early Triassic	Russia	A basal trematosauroid stereospondyl amphibian, originally thought to be a capitosaur.
Edingerella	Induan to Smithian	Madagascar	A capitosaurian stereospondyl closely related to Watsonisuchus.
Meyerosuchus	Early Triassic	Germany	A capitosaurian stereospondyl amphibian
Odenwaldia	Spathian	Germany	A capitosaurian stereospondyl amphibian
Parotosuchus	Early Triassic	Europe; Central Asia	A widespread and diverse genus of capitosaurian stereospondyl amphibian.
Platycepsion	Late Spathian - Early Anisian	Terrigal Formation, Australia	A brachyopid stereospondyl amphibian.
Rhytidosteus	Early Triassic	Astrakhan Oblast, Russia	A rhytidosteid stereospondyl amphibian.
Stanocephalosaurus	Middle Triassic	Africa; North America	A capitosaurian stereospondyl amphibian
Sclerothorax		Germany	A capitosaurian stereospondyl amphibian
Thoosuchus	Early Triassic	Russia	A basal trematosauroid stereospondyl amphibian, superficially resembling more derived trematosauroids.
Trematosaurus	Early Triassic	Russia	A trematosaurid stereospondyl amphibian
Vladlenosaurus	Late Vetlugian	Russia	A capitosaurian stereospondyl amphibian
Wetlugasaurus W. angustifrons W. malachovi	W. angustifrons: Sludkian Gorizont W. malachovi: Ustmylian Gorizont	Russia and Greenland	A capitosaurid stereospondyl amphibian, used as an index fossil.

†Chroniosuchians

Chroniosuchia of the Olenekian
Taxa	Presence	Location	Description	Images
Axitectum		Russia		Axitectum Bystrowiana
Bystrowiana	Lopingian to Early Triassic	Russia, China
Dromotectum Dromotectum spinosum	Early Triassic	Russia

†Procolophonomorphs

Procolophonomorpha of the Olenekian
Taxa	Presence	Location	Description	Images
Anomoiodon	early Olenekian	Solling Formation, Thuringia, Germany	A species of procolophonid parareptile in the subfamily Procolophoninae.	Sclerosaurus
Eumetabolodon bathycephalus	Olenekian to earliest Anisian	Zhuengeerqi locality, upper Heshanggou Formation, Ordos Basin, China	A species of procolophonid parareptile in the subfamily Procolophoninae.
Kapes	Lower and Middle Triassic	Russia	A genus of procolophonid parareptile in the subfamily Procolophoninae.
Sclerosaurus	Early Triassic	Germany, Switzerland	A genus of lizard-shaped procolophonid parareptile in the subfamily Leptopleuroninae.
Tichvinskia	Early Triassic	Russia	A species of procolophonid parareptile.

Archosauromorphs

Archosauromorphs of the Olenekian
Taxa	Presence	Location	Description	Images
Augustaburiania		Volgograd Oblast, Russia	The oldest known tanystropheid.	Chasmatosuchus Ctenosauriscus Erythrosuchus Garjainia Prolacerta Proterosuchus
Boreopricea		Kolguyev Island, arctic Russia	A basal archosauromorph reptile of controversial classification, various studies have considered it a close relative of Prolacerta, tanystropheids, both, or neither.
Bystrowisuchus		Lipovskaya Formation, Russia	A ctenosauriscid suchian.
Chasmatosuchus		South Africa, China	A proterosuchid that is one of the earliest well-known archosauriforms. It was over 2 meters (6 ft) long and is thought to have behaved like a modern crocodile. Its mouth had two distinct features: the top of its jaw hooked downwards to aid in holding prey, and the upper palate was lined with a row of teeth (a primitive feature lost in later archosaurs).
Ctenosauriscus		Solling Formation, Germany	A ctenosauriscid suchian. Ctenosauriscus is one of the oldest archosaurs known to date.
Czatkowiella	Early Triassic	Poland
Erythrosuchus	250–237.2 Ma, Olenekian to Ladinian	Omingonde Formation, Namibia South Africa	The largest erythrosuchid. One of its few distinguishing features other than its size is the smoothness of the margin of the squamosal. In other erythrosuchids, the margin of this bone projects backward from the skull, giving it a hook-like appearance. In Erythrosuchus, the margin is convex and lacks a hook.
Exilisuchus	247.3-245 Ma, Olenekian to Anisian	Russia	A potentially dubious archosauromorph of uncertain affinities. Initially believed to be a proterosuchid archosauriform, a 2016 analysis found that it also shared features with tanystropheids.
Garjainia		Russia	An erythrosuchid approximately 1.50–2 meters (5–6 ft 8 in) long.
Prolacerta	~252–247 Ma, Induan to Olenekian	Katberg Formation, East Cape, South Africa	Initially considered to be ancestral to modern lizards, a later study instead found that it shared more similarities with the lineage that would lead to archosaurs.
Proterosuchus	252-250 Ma, Induan to Olenekian	South Africa China	A proterosuchid that was one of the largest land reptiles during the Early Triassic. It looked somewhat similar to a primitive crocodilian, and shared many of their modern features like long jaws, powerful neck muscles, short legs and a lengthy tail, while possessing several features unique to proterosuchids such as its hook-shaped mouth and long rows of simple cone-shaped teeth. This jaw may have been an adaptation for catching prey, such as Lystrosaurus.
Scythosuchus		Russia,	Possibly a rauisuchid. Scythosuchus was between 2 and 3 metres long, and relatively heavily built.
Tasmaniosaurus	Induan to Olenekian	Knocklofty Formation, West Hobart, Tasmania	Once believed to be a proterosuchid, this taxon is now believed to have been intermediate between advanced non-archosauriform archosauromorphs such as Prolacerta, and basal archosauriforms such as Proterosuchus. This genus is also notable being one of the most complete Australian Triassic reptiles known.
Tsylmosuchus	Induan to Olenekian	Southern Urals, Russia	Originally classified as a rauisuchid, Tsylmosuchus has more recently been interpreted as an indeterminate archosauriform. Tsylmosuchus occurred throughout the Olenekian age. Some of the strata from which Tsylmosuchus has been found are Induan in age, making it one of the earliest archosaurs.
Vytshegdosuchus	latest Olenekian	Yarenskian Gorizont, Komi Republic, Russia	A genus of paracrocodylomorph archosaur, possibly a rauisuchid, and the oldest known archosaur from Russia.
Xilousuchus		Heshanggou Formation, China	A ctenosauriscid suchian. Xilousuchus is one of the oldest archosaurs known to date.

†Sauropterygia

Sauropterygians of the Olenekian
Taxa	Presence	Location	Description	Images
Corosaurus	Late Olenekian	United States, Wyoming	A pistosaur.	Corosaurus
Hanosaurus	Olenekian	China	A possible pachypleurosaur.
Majiashanosaurus	Olenekian	China	A possible pachypleurosaur.

†Hupehsuchians

†Hupehsuchia of the Olenekian
Taxa	Presence	Location	Description	Images
Eohupehsuchus	Early Triassic	China	An ichthyosauromorph	Hupehsuchus Unnamed polydactylous hupehsuchian
Eretmorhipis	Early Triassic	China	An ichthyosauromorph
Hupehsuchus	Early Triassic	China	An ichthyosauromorph
Nanchangosaurus	Early Triassic	China	An ichthyosauromorph
Parahupehsuchus	Early Triassic	China	An ichthyosauromorph

†Ichthyosauriforms

†Ichthyosauriformes of the Olenekian
Taxa	Presence	Location	Description	Images
Cartorhynchus	Early Triassic	China	An early ichthyosauriform	Cartorhynchus Sclerocormus
Sclerocormus	Early Triassic	China	An early ichthyosauriform

†Ichthyopterygians

†Ichthyopterygia of the Olenekian
Taxa	Presence	Location	Description	Images
Chaohusaurus	Early Triassic	China		Chaohusaurus Grippia Omphalosaurus Utatsusaurus
Grippia	Early Triassic	Canada, Japan, Greenland, China
Omphalosaurus	Early Triassic to Middle Triassic	Svalbard	An early ichthyosauriform with button-like teeth
Quasianosteosaurus	Early Triassic	Svalbard
Utatsusaurus	Early Triassic	Miyagi Prefecture, Japan; British Columbia, Canada	An early ichthyosauriform

Therapsids

Therapsids of the Olenekian
Taxa	Presence	Location	Description	Images
Kannemeyeria		Burgersdorp Formation, South Africa Ntawere Formation, Zambia Omingonde Formation, Namibia Manda Formation, Tanzania	A kannemeyeriid that was one of the first representatives of the family, and hence one of the first large herbivores of the Triassic. Although it had a large head, it was lightweight due to the size of the eye sockets and nasal cavity. It also had limb girdles which formed massive plates of bone that helped support its heavily built body.
Lystrosaurus		Fremouw Formation, Antarctica	A common genus of dicynodonts.
Trirachodon		Driekoppen Formation, Free State, South Africa Omingonde Formation, Namibia	A cynodont.

• GeoWhen Database - Olenekian
• Lower Triassic timescale at the website of the subcommission for stratigraphic information of the ICS
• Lower Triassic timescale at the website of Norges Network of offshore records of geology and stratigraphy.