The Induan is, in the geologic timescale, the first age of the Early Triassic

Early Triassic

The Early Triassic is the first of three epochs of the Triassic period of the geologic timescale. It spans the time between 251 ± 0.4 Ma and 245 ± 1.5 Ma . Rocks from this epoch are collectively known as the Lower Triassic, which is a unit in chronostratigraphy...

 epoch

Epoch (geology)

An epoch is a subdivision of the geologic timescale based on rock layering. In order, the higher subdivisions are periods, eras and eons. We are currently living in the Holocene epoch...

 or the lowest stage of the Lower Triassic series

Series (stratigraphy)

Series are subdivisions of rock layers made based on the age of the rock and corresponding to the dating system unit called an epoch, both being formally defined international conventions of the geological timescale. A series is therefore a sequence of rock depositions defining a...

. It spans the time between 251 ± 0.4 Ma and 249.7 ± 0.7 Ma (million years ago). It is preceded by the Changhsingian

Changhsingian

In the geologic timescale, the Changhsingian or Changxingian is the latest age or uppermost stage of the Permian. It is also the upper or latest of two subdivisions of the Lopingian epoch or series. The Changhsingian lasted from 253.8 ± 0.7 to 251.0 ± 0.7 million years ago...

 and is followed by the Olenekian

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 249.7 ± 0.7 Ma and 245 ± 0.7 Ma . The Olenekian follows the Induan and is followed by the Anisian.The Olenekian saw the deposition of a large part of the...

.

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

China

Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...

.

Stratigraphic definitions

The Induan stage was introduced into scientific literature by Russian stratigraphers in 1956, who divided the Skythian stage that was used by Western stratigraphers into the Induan and Olenekian stages. 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

Mesozoic

The Mesozoic era is an interval of geological time from about 250 million years ago to about 65 million years ago. It is often referred to as the age of reptiles because reptiles, namely dinosaurs, were the dominant terrestrial and marine vertebrates of the time...

 erathem

Erathem

In stratigraphy, paleontology, geology, and geobiology an erathem is the total stratigraphic record deposited during a certain corresponding span of time, an era in the geologic timescale....

) is defined as the place in the fossil record where the conodont

Conodont

Conodonts are extinct chordates resembling eels, classified in the class Conodonta. For many years, they were known only from tooth-like microfossils now called conodont elements, found in isolation. Knowledge about soft tissues remains relatively sparse to this day...

 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

Changxing County

Changxing County is a county in the prefecture-level city of Huzhou, Zhejiang, China. Situated in the northern part of Zhejiang Province, it is close to the border of Zhejiang, Jiangsu, Anhui Province and serves as an important city in transportation.Changxing has since 2004 a Twin City ...

, China.

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, it still contains five ammonite biozone

Biozone

Biostratigraphic units or Biozones are intervals of geological strata that are defined on the basis of their characteristic fossil taxa....

s in the boreal domain and four ammonite biozones in the Tethyan domain

Tethys Ocean

The Tethys Ocean was an ocean that existed between the continents of Gondwana and Laurasia during the Mesozoic era before the opening of the Indian Ocean.-Modern theory:...

.

Palaeontology

The Induan age followed the mass extinction event

Permian-Triassic extinction event

The Permian–Triassic extinction event, informally known as the Great Dying, was an extinction event that occurred 252.28 Ma ago, forming the boundary between the Permian and Triassic geologic periods, as well as the Paleozoic and Mesozoic eras...

 at the end of the Permian

Permian

The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...

 period. Both global biodiversity

Biodiversity

Biodiversity is the degree of variation of life forms within a given ecosystem, biome, or an entire planet. Biodiversity is a measure of the health of ecosystems. Biodiversity is in part a function of climate. In terrestrial habitats, tropical regions are typically rich whereas polar regions...

 and community

Community (ecology)

In ecology, a community is an assemblage of two or more populations of different species occupying the same geographical area. The term community has a variety of uses...

-level (alpha) diversity

Biodiversity

Biodiversity is the degree of variation of life forms within a given ecosystem, biome, or an entire planet. Biodiversity is a measure of the health of ecosystems. Biodiversity is in part a function of climate. In terrestrial habitats, tropical regions are typically rich whereas polar regions...

 remained low through much of this stage of the Triassic. 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 ammonite

Ammonite

Ammonite, as a zoological or paleontological term, refers to any member of the Ammonoidea an extinct subclass within the Molluscan class Cephalopoda which are more closely related to living coleoids Ammonite, as a zoological or paleontological term, refers to any member of the Ammonoidea an extinct...

s, fishes, insects, and the tetrapods (cynodont

Cynodont

Cynodontia or cynodonts are a taxon of therapsids which first appeared in the Late Permian and were eventually distributed throughout all seven continents by the Early Triassic . This clade includes modern mammals and their extinct close relatives. They were one of the most diverse groups of...

s, amphibian

Amphibian

Amphibians , are a class of vertebrate animals including animals such as toads, frogs, caecilians, and salamanders. They are characterized as non-amniote ectothermic tetrapods...

s, reptile

Reptile

Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...

s, etc.) remained rare and terrestrial ecosystems did not recover for 30M years. Both the seas and much of the freshwater during the Induan were anoxic

Hypoxia (environmental)

Hypoxia, or oxygen depletion, is a phenomenon that occurs in aquatic environments as dissolved oxygen becomes reduced in concentration to a point where it becomes detrimental to aquatic organisms living in the system...

.

• lystrosaurids
  Lystrosaurus
  Lystrosaurus was a genus of Late Permian and Early Triassic Period dicynodont therapsids, which lived around 250 million years ago in what is now Antarctica, India, and South Africa...
  
  
• proterosuchids
  Proterosuchidae
  Proterosuchidae is an early, possibly paraphyletic, assemblage of basal archosauriformes whose fossils are known from the Latest Permian of Russia and the Early Triassic of southern Africa, Russia, China, Australia, and Antarctica...
  
  

Archosaurs

Archosaurs of the Induan
Taxa	Presence	Location	Description	Images
Proterosuchus Proterosuchus Proterosuchus is an extinct genus of Early Triassic proterosuchid archosaur. Remains have been found from South Africa and China. The genus Chasmatosaurus is considered a junior synonym of Proterosuchus, as all species of Chasmatosaurus, including C. aleandri, C. vanhoepeni, and C. yuani, have...		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.
Prolacerta		South Africa, Fremouw Formation Fremouw Formation The Fremouw Formation is a Triassic-age rock formation in the Transantarctic Mountains of Antarctica. Fossils of prehistoric reptiles and amphibians have been found in the formation. Fossilized trees have also been found. The formation's beds were deposited along the banks of rivers and on... , Antarctica

†Conodonts

†Conodonts of the Induan
Taxa	Presence	Location	Description	Images
Hindeodus parvus Hindeodus parvus Hindeodus parvus is an extinct species of conodont whose first appearance in the fossil beds at Meishan, Changxing County, Zhejiang marks the base of the Triassic, and thus the boundary between the Triassic and Permian.-References:...

Procolophonomorphs

Procolophonomorpha Procolophonomorpha Procolophonomorpha is an order or clade of early reptiles that appeared during the Middle Permian. It constitutes a diverse assemblage that includes a number of lizard-like forms, as well as more diverse types like the pareiasaurs. The most important subclade, Procolophonia, is traditionally...  of the Induan
Taxa	Presence	Location	Description	Images
Procolophon Procolophon Procolophon was a genus of lizard-like procolophonid reptiles with at least eight species that persisted through the Permian–Triassic extinction event, but became extinct in the later Triassic....	Late Permian to Late Triassic Late Triassic The Late Triassic is in the geologic timescale the third and final of three epochs of the Triassic period. The corresponding series is known as the Upper Triassic. In the past it was sometimes called the Keuper, after a German lithostratigraphic group that has a roughly corresponding age...	South Africa	A genus of lizard-shaped reptiles
Nyctiphruretus Nyctiphruretus Nyctiphruretus , is an extinct genus of reptiles distantly related to turtles. The reptiles lived around about 250 million years ago and looked more like lizards than turtles....	Induan/Olenekian 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 249.7 ± 0.7 Ma and 245 ± 0.7 Ma . The Olenekian follows the Induan and is followed by the Anisian.The Olenekian saw the deposition of a large part of the...	Mezen River Mezen River The Mezen is a river in Udorsky District of the Komi Republic and in Leshukonsky and Mezensky Districts of Arkhangelsk Oblast in Russia. Its mouth is located in the Mezen Bay of the White Sea. Mezen is one of the biggest rivers of European Russia. It is long, and the area of its basin... , European Russia	A lizard-like looking reptile which diet consisted of aquatic plants. Adults discovered averaged 36 cm in length with a 4.4 cm skull

†Temnospondyls

†Temnospondyli Temnospondyli Temnospondyli is a diverse order of small to giant tetrapods—often considered primitive amphibians—that flourished worldwide during the Carboniferous, Permian, and Triassic periods. A few species continued into the Cretaceous. Fossils have been found on every continent...  of the Induan
Taxa	Presence	Location	Description	Images
Wetlugasaurus Wetlugasaurus Wetlugasaurus is an extinct genus of temnospondyl amphibian from the Early Triassic of northern Russia and Greenland.-References:* The Age of Dinosaurs in Russia and Mongolia by Michael J. Benton, Mikhail A. Shishkin, David M. Unwin, and Evgenii N. Kurochkin. p. 35-59.* Bibliography Of Fossil...		Northern Russia

†Therapsids (non-mammalian)

†Non-mammalian Paraphyly A group of taxa is said to be paraphyletic if the group consists of all the descendants of a hypothetical closest common ancestor minus one or more monophyletic groups of descendants...  Therapsids of the Induan
Taxa	Presence	Location	Description	Images
Galesaurus Galesaurus Galesaurus was a prehistoric mammal-like-reptile, incorrectly classified as a dinosaur by Sir Richard Owen in 1859. Notably, Galesaurus was mentioned in the first issue of Nature in 1869, where T. H. Huxley expressed confidence that it would eventually be shown to be a dinosaur...
Lystrosaurus Lystrosaurus Lystrosaurus was a genus of Late Permian and Early Triassic Period dicynodont therapsids, which lived around 250 million years ago in what is now Antarctica, India, and South Africa...	Late Permian to Early Triassic Early Triassic The Early Triassic is the first of three epochs of the Triassic period of the geologic timescale. It spans the time between 251 ± 0.4 Ma and 245 ± 1.5 Ma . Rocks from this epoch are collectively known as the Lower Triassic, which is a unit in chronostratigraphy...	Antarctica, India and South Africa	The most common group of terrestrial vertebrates during the Early Triassic: for a while 95% of land vertebrates were Lystrosaurus
Scaloposaurus Scaloposaurus Scaloposaurus is an extinct carnivorous genus of therocephalian living during the Triassic 251.0—245.0 Ma existing for approximately .-Taxonomy:...			A therocephalian
Thrinaxodon Thrinaxodon Thrinaxodon was a cynodont, an ermine-sized therapsid. Pits on the skull suggest that Thrinaxodon may have had whiskers, and by extension a protective covering of fur. There are suggestions that it was warm-blooded...	?	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 had a reptilian skeleton and laid eggs.

Literature

; 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.; 2004: A Geologic Time Scale 2004, Cambridge University Press

Cambridge University Press

Cambridge University Press is the publishing business of the University of Cambridge. Granted letters patent by Henry VIII in 1534, it is the world's oldest publishing house, and the second largest university press in the world...

.; 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 .

External links

• GeoWhen Database - Induan
• 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.
• The Induan at palaeos.com