Olenekian

In the geologic timescale, the Olenekian is an age in the Early Triassic epoch or a stage in the Lower Triassic series. It spans the time between 251.2 Ma and 247.2 Ma (million years ago).^[1] The Olenekian follows the Induan and is followed by the Anisian.^[2]

The Olenekian saw the deposition of a large part of the Buntsandstein in Europe. Archosaurs - a group encompassing crocodiles, pterosaurs, dinosaurs, and ultimately birds - are diapsid reptiles that first evolved from Archosauriform ancestors during the Olenekian.

The Olenekian is roughly coeval with the regional Yongningzhenian stage used in China.

Stratigraphic definitions

The Olenekian stage was introduced into scientific literature by Russian stratigraphers in 1956.^[3] 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 ammonites Hedenstroemi 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 in 2009 not yet been established.

The Olenekian is sometimes divided into the Smithian and the Spathian subages or substages.

Palaeontology

• Gnathorhizids

• Archosaurs
• Erythrosuchids
• Proterosuchids
• Crurotarsi
  • Rauisuchia

Archosauromorphs

Archosauromorphs of the Olenekian
Taxa	Presence	Location	Description	Images
Augustaburiania		Volgograd Oblast, Russia	The oldest known tanystropheid.	Chasmatosuchus Erythrosuchus Garjainia Proterosuchus
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).
Erythrosuchus	250-237.2 Ma, Olenekian to Ladinian	South Africa Omingonde Formation, Namibia	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
Garjainia		Russia	An erythrosuchid approximately 1.50–2 meters (5–6 ft 8 in) long.
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.

†Ichthyopterygians

†Ichthyopterygia of the Olenekian
Taxa	Presence	Location	Description	Images
Chaohusaurus		China		Chaohusaurus Grippia Utatsusaurus
Grippia		Canada Japan Greenland China
Utatsusaurus		Miyagi Prefecture, Japan British Columbia, Canada

Therapsids

Therapsids of the Olenekian
Taxa	Presence	Location	Description	Images
Cynognathus	247.2-237 Ma, Olenekian to Ladinian	South Africa China Argentina Lesotho Antarctica	A large-bodied cynodont that had an almost worldwide distribution. Its dentary was equipped with differentiated teeth that show this animal could effectively process its food before swallowing.	Cynognathus Kannemeyeria Lystrosaurus Scaloposaurus Trirachodon
Kannemeyeria		South Africa Argentina India	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		Antarctica India South Africa
Scaloposaurus		South Africa
Trirachodon		Driekoppen Formation, Free State, South Africa Omingonde Formation, Namibia

See also

• Geologic time scale

References

Notes

Literature

• Brack, P.; Rieber, H.; Nicora, A. & Mundil, R.; 2005: The Global boundary Stratotype Section and Point (GSSP) of the Ladinian Stage (Middle Triassic) at Bagolino (Southern Alps, Northern Italy) and its implications for the Triassic time scale, Episodes 28(4), pp. 233–244.
• Gradstein, F.M.; Ogg, J.G. & Smith, A.G.; 2004: A Geologic Time Scale 2004, Cambridge University Press.
• Kiparisova, L.D. & Popov, J.N.; 1956: Расчленение нижнего отдела триасовой системы на ярусы (Subdivision of the lower series of the Triassic System into stages), Doklady Akademii Nauk SSSR 109(4), pp 842–845 (Russian).

External links

• 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.