Olenekian

The Olenekian is a special time period in Earth's history. It is part of the Early Triassic, which is a time long, long ago. The Olenekian happened between 249.9 million and 246.7 million years ago. We know this by looking at rocks and fossils from that time.

During the Olenekian, many important rocks were formed, especially in a place called the Buntsandstein in Europe. This helps scientists understand what the world was like back then.

The Olenekian comes after another time called the Induan and before a time called the Anisian. Sometimes, it is split into two smaller parts named the Smithian and the Spathian. In China, scientists use a different name, Yongningzhenian, for about the same time.

Stratigraphic definitions

The Olenekian Stage was introduced into scientific literature by Russian scientists in 1956. It is named after Olenëk in Siberia. Before this, the Olenekian and another stage called the Induan were part of a group known as the Scythian Stage.

Scientists use special fossils, like certain types of ammonoids and conodonts, to mark the beginning and end of the Olenekian. In the 1960s, a scientist named Edward T. Tozer created a timeline for the Triassic period using fossils found in North America. He suggested dividing the Lower Triassic into four parts, two of which are similar to the Olenekian. He named these parts after creeks in Canada.

Olenekian life

See also: Category:Olenekian life

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. 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 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. Ammonoids and conodonts diversified but both suffered losses during the Smithian-Spathian boundary extinction at the end of the Smithian subage.

Ray-finned fishes largely remained unaffected by the Permian-Triassic extinction event. Coelacanths show their highest post-Devonian diversity during the Early Triassic. Many fish genera show a cosmopolitan distribution during the Induan and Olenekian. Ray-finned fishes diversified after the mass extinction and reached peak diversity during the Middle Triassic.

The first marine reptiles appeared during the Olenekian. Hupehsuchia, Ichthyopterygia and Sauropterygia are among the first marine reptiles to enter the scene.

An example of an exceptionally diverse Early Triassic assemblage is the Paris biota, fossils of which were discovered near Paris, Idaho and other nearby sites in Idaho and Nevada. The Paris Biota was deposited in the wake of the SSBM and it features at least 7 phyla and 20 distinct metazoan orders, including several types of sponges, crustaceans, nautiloids, ammonoids, and vertebrates.

Notable formations

Some important rock layers from the Olenekian period are found in many places around the world. These include the Middle Buntsandstein in Germany, the Jialingjiang Formation in South China, and the Nanlinghu Formation in Anhui, China. Other notable formations are the Sulphur Mountain Formation in British Columbia, Canada, the Thaynes Group/Limestone in the western USA, the Virgin Formation in Utah, USA, and the Vikinghøgda Formation in Svalbard, Norway.