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Lower Triassic

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Sandstone from the Lower Triassic epoch
Proterosuchus, an early crocodile-type archosaur

The Lower Triassic is the first of three epochs of the Triassic period. It lasted from about 252.2 million years ago (mya) to ~247.2 mya. The Lower Triassic is the oldest epoch of the Mesozoic era. These rocks were laid down just after the great Permian–Triassic extinction event.

The Lower Triassic was called the Scythian stage, which can be found in older literature. In Europe, most of the Lower Triassic is composed of sandstone. It is a lithostratigraphic unit of continental red beds. They were formed on land under desert conditions.

Fauna[change | change source]

The massive extinctions that ended the Paleozoic era caused extreme hardship for the surviving species. Many types of corals, brachiopods, molluscs, echinoderms, and other invertebrates had completely disappeared. The most common hard-shelled marine invertebrates were bivalves, gastropods, ammonites, echinoids, and a few articulate brachiopods. The most common land animal was the herbivorous synapsid Lystrosaurus.

The earliest Triassic faunas lacked biodiversity and were like that throughout the epoch. Recovery on land took 30 million years.[1]

The first ichthyosaurs evolved in this epoch. The largest ichthyosaurs known come from the Triassic.

The climate during the Lower Triassic (especially in the interior of the supercontinent Pangaea) was generally dry. Deserts were widespread. The poles had a temperate climate. The relatively hot climate of the epoch may have been caused by widespread volcanic eruptions.

On land, the plants included the lycophytes, the dominant cycadophytes, ginkgophyta (represented in modern times by Ginkgo biloba), ferns, horsetails and glossopteris.

Map showing where in the world fossils of this animal were found. It indicates that the animal's range extended to South Africa, India, and Antarctica. Other animals include a land reptile, swimming reptile, and a plant, and show that the continents were all joined together once.
Geographical distribution of Lystrosaurus      and contemporary fossils in Gondwana.

References[change | change source]

  1. Sahney S. and Benton M.J. (2008). "Recovery from the most profound mass extinction of all time". Proceedings of the Royal Society: Biological. 275 (1636): 759–65. doi:10.1098/rspb.2007.1370. PMC 2596898. PMID 18198148.