Olenekian

The Olenekian is an important time in Earth's history. It is part of the Early Triassic epoch. This time happened a very long time ago. The Olenekian lasted from about 249.9 million years ago to 246.7 million years ago.

During the Olenekian, important changes were happening on our planet. One big change was the formation of rocks called the Buntsandstein in Europe. These rocks help us learn about Earth from that time. The Olenekian is also linked to a stage called the Yongningzhenian in China.

The Olenekian came after a time called the Induan. It was followed by the Anisian, which is part of the Middle Triassic. Scientists split the Olenekian into two smaller parts. These parts are called the Smithian and the Spathian. This helps scientists study the Olenekian better.

Stratigraphic definitions

The Olenekian Stage was first used by scientists from Russia in 1956. It is named after a place called Olenëk in Siberia. Before this, the time period was part of something called the Scythian Stage, but that name is no longer used.

Scientists decide when the Olenekian began by looking for special fossils, like certain types of ammonoids and tiny tooth-like fossils called conodonts. In the 1960s, a scientist named Edward T. Tozer helped organize the timeline of this ancient time using fossils found in North America. He split this period into parts called the Smithian and the Spathian, which are similar to the Olenekian.

Olenekian life

See also: Category:Olenekian life

Life was still getting better after a big change long ago. During the Olenekian, plants changed from ones called lycopod to others like gymnosperm and pteridophyte. This happened because the world got warmer and there was more precipitation. Conifers were the main plants for much of the Mesozoic. Land animals called archosaurs began to evolve from their earlier ancestors. This group includes animals like crocodiles, pterosaurs, dinosaurs, and birds.

In the oceans, simple microbial reefs were common, partly because many reef builders were gone after the big change. But reefs made by animals came back during the Olenekian when conditions allowed. Ammonoids and conodonts became more diverse, but they lost some types at the end of the Smithian time.

Ray-finned fishes were not greatly affected by the big change. Coelacanths were more common then than before. Many fish types were found all over the world during the Induan and Olenekian, like Australosomus, Birgeria, Parasemionotidae, Pteronisculus, Ptycholepidae, Saurichthys and Whiteia. Ray-finned fishes became more diverse after the big change and were very common in the Middle Triassic.

Olenekian chondrichthyan fishes included hybodonts and neoselachians, along with some older types like eugeneodontid holocephalians.

Ocean amphibians called temnospondyl, like Aphaneramma and Wantzosaurus, lived in many places. Others, like Trematosaurus, lived in freshwater and were less common.

The first sea reptiles appeared during the Olenekian. Hupehsuchia, Ichthyopterygia and Sauropterygia were among the first, like Cartorhynchus, Chaohusaurus, Utatsusaurus, Hupehsuchus, Grippia, Omphalosaurus, Corosaurus. These groups would become important ocean animals later.

An example of a rich collection of Early Triassic life is the Paris biota, found near Paris, Idaho and other places. The Paris Biota shows many different kinds of life, including sponges, crustaceans, nautiloids, ammonoids, and vertebrates.

Life restoration of _[Pleuromeia](/wiki/Pleuromeia)_, a plant that was common during the Olenekian

Skull of the [ray-finned fish](/wiki/Ray-finned_fish) _[Birgeria](/wiki/Birgeria) americana_

Skull of the [temnospondyl](/wiki/Temnospondyl) amphibian _[Trematosaurus](/wiki/Trematosaurus) brauni_

Skull of the [archosauriform](/wiki/Archosauriform) reptile _[Erythrosuchus](/wiki/Erythrosuchus) africanus_

Marine [ichthyosauromorph](/wiki/Ichthyosauromorpha) reptile _[Chaohusaurus](/wiki/Chaohusaurus)_

Smithian–Spathian boundary event

A big change happened during the Olenekian, near the end of the Smithian time. This change hurt many animals that had survived earlier difficult times. Ammonoids, conodonts and other sea animals lost many types. On land, plants changed from lycopod-dominated to ones like gymnosperm and pteridophyte. This was because of changes in temperature and precipitation.

The change in the ocean and on land happened because of big volcanic eruptions. These released gases that warmed the Earth and changed the chemistry of the oceans. Some scientists think a spike in mercury also played a role, but this is not certain.

In the ocean, many large sea animals moved away from warm areas, but some stayed. On land, it was very dry and hot in some places. Life came back when conditions improved.

There are places that show many different kinds of life, suggesting that ecosystems became complex again.

Notable formations

Some important rock layers from the Olenekian time include the Middle Buntsandstein in Germany and the Jialingjiang Formation in South China. Other notable formations are the Nanlinghu Formation in Anhui, China, the Sulphur Mountain Formation in British Columbia, Canada, and several layers in the western USA such as the Thaynes Group/Limestone. Additional formations include the Virgin Formation in Utah, USA, and the Vikinghøgda Formation in Svalbard, Norway.