Induan

System/
Period		 Series/
Epoch		 Stage/
Age		 Age (Ma)
Jurassic Lower/
Early		 Hettangian younger
Triassic Upper/
Late		 Rhaetian 201.3 ~208.5
Norian ~208.5 ~227
Carnian ~227 ~237
Middle Ladinian ~237 ~242
Anisian ~242 247.2
Lower/
Early		 Olenekian 247.2 251.2
Induan 251.2 251.902
Permian Lopingian Changhsingian older
Subdivision of the Triassic system
according to the ICS, as of 2018.[1]

The Induan is, in the geologic timescale, the first age of the Early Triassic epoch or the lowest stage of the Lower Triassic series. It spans the time between 251.902 Ma and 251.2 Ma (million years ago).[2] It is preceded by the Changhsingian and is followed by the Olenekian.

The Induan is roughly coeval with the regional Feixianguanian stage of China.

Stratigraphic definitions

The Induan stage was introduced into scientific literature by Russian stratigraphers in 1956,[3] who divided the Scythian stage that was used by Western stratigraphers into the Induan and Olenekian stages. The Induan stage is named for the Indus region of Pakistan/India.[4] The Russian subdivision of the Lower Triassic then slowly replaced the one used in the West.

The base of the Induan stage (which is also the base of the Lower Triassic series, the base of the Triassic system and the base of the Mesozoic erathem) is defined as the place in the fossil record where the conodont species Hindeodus parvus first appears, or at the end of the negative δ18O anomaly after the big extinction event at the Permian-Triassic boundary. The global reference profile of the base of the Induan is situated in Changxing County, China.[5]

The top of the Induan stage (the base of the Olenekian) is at the first appearance of ammonite species Meekoceras gracilitatis.

Though the Induan is an unusually short age at this point in the geologic timescale, its million years' extent still contains five ammonite biozones in the boreal domain and four ammonite biozones in the Tethyan domain.

Palaeontology

The Induan age followed the mass extinction event at the end of the Permian period. Both global biodiversity and community-level (alpha) diversity remained low through much of this stage of the Triassic.[6] Much of the world remained almost lifeless, deserted, hot, and dry. The lystrosaurids (below) and the proterosuchids (below) were the only groups of land animals to dominate during the Induan stage. Other animals, such as the ammonites, fishes, insects, and the tetrapods (cynodonts, amphibians, reptiles, etc.) remained rare and terrestrial ecosystems did not recover for some 30 million years.[6] Both the seas and much of the freshwater during the Induan were anoxic.

Archosauromorphs

Archosauromorphs of the Induan
Taxa Presence Location Description Images
South Africa, Fremouw Formation, Antarctica
Prolacerta
Proterosuchus
South Africa The largest land reptile during the Early Triassic period, equivalent in size to today's Komodo Dragons. It looked somewhat similar to a primitive crocodile, and shared many of their modern features like long jaws, powerful neck muscles, short legs and a lengthy tail, while retaining several of its own unique features such as its long legs, and hooked shaped mouth.

†Conodonts

†Conodonts of the Induan
Taxa Presence Location Description Images
China

Procolophonomorphs

Procolophonomorpha of the Induan
Taxa Presence Location Description Images
Late Permian to Late Triassic South Africa A genus of lizard-shaped reptiles
Procolophon

Temnospondyls

Temnospondyli of the Induan
Taxa Presence Location Description Images
Northern Russia
Wetlugasaurus

Therapsids

Therapsids of the Induan
Taxa Presence Location Description Images
Galesaurus
Lystrosaurus
Regisaurus
Scaloposaurus
Thrinaxodon
Late Permian to Early Triassic Antarctica, Russia, India and South Africa The most common group of terrestrial vertebrates during the Early Triassic: for a while 95% of land vertebrates were Lystrosaurus
Late Permian to Early Triassic South Africa
A therocephalian
Early Triassic South Africa, Antarctica A cat-sized cynodont. Many scientists suggest that the pits on the skull indicate that Thrinaxodon had whiskers and, therefore, probably had a covering of fur. There are suggestions that it was warm-blooded. Even so, it still laid eggs.

References

  1. ↑ "International Chronostratigraphic Chart" (PDF). International Commission on Stratigraphy. 2018.
  2. ↑ http://www.stratigraphy.org/index.php/ics-chart-timescale
  3. ↑ Kiparisova & Popov (1956)
  4. ↑ The Triassic Timescale, Spencer Lucas (2010), ISBN 9781862392960
  5. ↑ Yin Hongfu, Zhang Kexin, Tong Jinnan, Yang Zunyi und Wu Shunbao: '"The Global Stratotype Section and Point (GSSP)of the Permian-Triassic Boundary." Episodes, 24(2): 102-114, Beijing 2001 ISSN 0705-3797.
  6. 1 2 Sahney, S.; Benton, M.J. (2008). "Recovery from the most profound mass extinction of all time" (PDF). Proceedings of the Royal Society B: Biological Sciences. 275 (1636): 759–65. doi:10.1098/rspb.2007.1370. PMC 2596898. PMID 18198148.

Sources

  • 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, Lubov Dmitrievna & Popov, Yurij Nikolaivitch; 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 (in Russian).

Coordinates: 31°04′47″N 119°42′21″E / 31.0797°N 119.7058°E / 31.0797; 119.7058

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