The Toarcian is, in the ICS

International Commission on Stratigraphy

The International Commission on Stratigraphy , sometimes referred to by the unofficial "International Stratigraphic Commission" is a daughter or major subcommittee grade scientific daughter organization that concerns itself with stratigraphy, geological, and geochronological matters on a global...

' geologic timescale, an age or stage in the Early or Lower Jurassic

Early Jurassic

The Early Jurassic epoch is the earliest of three epochs of the Jurassic period...

. It spans the time between 183.0 Ma (million years ago) and 175.6 Ma. It follows the Pliensbachian

Pliensbachian

The Pliensbachian is an age of the geologic timescale or stage in the stratigraphic column. It is part of the Early or Lower Jurassic epoch or series and spans the time between 189.6 ± 1.5 Ma and 183 ± 1.5 Ma . The Pliensbachian is preceded by the Sinemurian and followed by the Toarcian.The...

 and is followed by the Aalenian

Aalenian

The Aalenian is a subdivision of the Middle Jurassic epoch/series of the geologic timescale that extends from about 175.6 Ma to about 171.6 Ma . It was preceded by the Toarcian and succeeded by the Bajocian.-Stratigraphic definitions:...

.

The Toarcian age began with the Toarcian turnover

Toarcian turnover

The term Toarcian turnover, alternatively the Toarcian extinction, the Pliensbachian-Toarcian extinction, or the Early Jurassic extinction, refers to the wave of extinctions that marked the end of the Pliensbachian stage and the start of the Toarcian stage of the Early Jurassic period, c...

, the extinction event

Extinction event

An extinction event is a sharp decrease in the diversity and abundance of macroscopic life. They occur when the rate of extinction increases with respect to the rate of speciation...

 that sets its fossil faunas apart from the previous Pliensbachian age.

Stratigraphic definitions

The Toarcian takes its name from the city of Thouars

Thouars

Thouars is a commune in the Deux-Sèvres department in western France.It is on the River Thouet. Its inhabitants are known as Thouarsais.-History:...

, just south of Saumur

Saumur

Saumur is a commune in the Maine-et-Loire department in western France.The historic town is located between the Loire and Thouet rivers, and is surrounded by the vineyards of Saumur itself, Chinon, Bourgueil, Coteaux du Layon, etc...

 in the Loire Valley

Loire Valley

The Loire Valley , spanning , is located in the middle stretch of the Loire River in central France. Its area comprises approximately . It is referred to as the Cradle of the French Language, and the Garden of France due to the abundance of vineyards, fruit orchards, and artichoke, asparagus, and...

 of France

France

The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...

. The stage was introduced by French palaeontologist Alcide d'Orbigny

Alcide d'Orbigny

Alcide Charles Victor Marie Dessalines d'Orbigny was a French naturalist who made major contributions in many areas, including zoology , palaeontology, geology, archaeology and anthropology....

 in 1842, after examining rock strata

Stratum

In geology and related fields, a stratum is a layer of sedimentary rock or soil with internally consistent characteristics that distinguish it from other layers...

 of this age in a quarry

Quarry

A quarry is a type of open-pit mine from which rock or minerals are extracted. Quarries are generally used for extracting building materials, such as dimension stone, construction aggregate, riprap, sand, and gravel. They are often collocated with concrete and asphalt plants due to the requirement...

 near Thouars.

In Europe this period is represented by the upper part of the Lias

Lias

Lias may refer to:*In geology:**The Lias Group, a group in the stratigraphy of Great Britain, formed during the Late Triassic to Early Jurassic epochs. It includes the Blue Lias and White Lias...

.

The base of the Toarcian is defined as the place in the stratigraphic record where 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...

 genus

Genus

In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 Eodactylites first appears. However, a global reference profile for the base of the Toarcian (a GSSP) had in 2009 not yet been assigned. The top of the stage is at the first appearance of ammonite genus Leioceras.

In the Tethys 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:...

, the Toarcian contains the following ammonite biozone

Biozone

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

s:

• zone of Pleydellia aalensis
• zone of Dumortieria pseudoradiosa
• zone of Phlyseogrammoceras dispansum
• zone of Grammoceras thouarcense
• zone of Haugia variabilis
• zone of Hildoceras bifrons
  Hildoceras
  Hildoceras is a genus of ammonite form the upper Lower Jurassic in the ammonitid family Hildoceratidae characterized by a narrow discoidal evolute shell, keeled venter, concave ribs along the outer flanks, and a shallow spiral goove running along smooth inner flanks. Whorls slightly overlap,...
  
  
• zone of Harpoceras serpentinum
• zone of Dactylioceras tenuicostatum
  Dactylioceras
  Dactylioceras was a widespread genus of ammonite from the Jurassic period, approximately 172 million years ago . They are generally small, averaging 65 mm in diameter....
  
  

†Ornithischians

Ornithischians of the Toarcian
Taxa	Presence	Location	Description	Images
Emausaurus Emausaurus Emausaurus is a genus of thyreophoran or armored dinosaur from the Early Jurassic. Its fossils have been found in Germany. It is known from a skull and partial postcranial remains, although only the skull is known well. Armor includes conical scutes and tall, spiny elements.The type species,...		Germany	Armored dinosaur known from a skull and partial postcranial remains, although only the skull is known well. Armor includes conical scutes and tall, spiny elements.

†Plesiosaurs

Plesiosauria Plesiosauria Plesiosauria is an order of Mesozoic marine reptiles. Plesiosaurs first appeared in the Early Jurassic Period and became especially common during the Jurassic Period, thriving until the K-T extinction at the end of the Cretaceous Period.The name "plesiosaur" is used to refer to the order...  of the Toarcian
Taxa	Presence	Location	Description	Images
Occitanosaurus Occitanosaurus Occitanosaurus is an extinct genus of plesiosaur from the Early Jurassic of what is now France. The type species is Occitanosaurus tournemirensis , first named by Sciau et al. in 1990...		Tournemire Tournemire Tournemire may refer to the following places in France:* Tournemire, Aveyron, a commune in the department of Aveyron* Tournemire, Cantal, a commune in the department of CantalIt may also refer to the following people:... , Aveyron, France	A plesiosaur similar to Elasmosaurus; fossils consist of a single but nearly complete skeleton of an animal approximately 4 meters (13 ft) long
Plesiosaurus Plesiosaurus Plesiosaurus was a genus of large marine sauropterygian reptile that lived during the early part of the Jurassic Period, and is known by nearly complete skeletons from the Lias of England...  guilelmiimperatoris	Sinemurian Sinemurian In the geologic timescale, the Sinemurian is an age or stage in the Early or Lower Jurassic epoch or series. It spans the time between 196.5 ± 2 Ma and 189.6 ± 1.5 Ma...  and Toarcian	Württemberg Württemberg Württemberg , formerly known as Wirtemberg or Wurtemberg, is an area and a former state in southwestern Germany, including parts of the regions Swabia and Franconia.... , Germany	A large (about 3 to 5 meters long), marine sauropterygian reptile, it was distinguished by its small head, long and slender neck, broad turtle like body, a short tail, and two pairs of large, elongated paddles
Rhomaleosaurus Rhomaleosaurus Rhomaleosaurus is an extinct genus of Early Jurassic rhomaleosaurid pliosauroid known from Northamptonshire and from Yorkshire of the United Kingdom. It was first named by Harry Seeley in 1874 and the type species is Rhomaleosaurus cramptoni...	Hettangian Hettangian The Hettangian is the earliest age or lowest stage of the Jurassic period of the geologic timescale. It spans the time between 199.6 ± 0.6 Ma and 196.5 ± 1 Ma . The Hettangian follows the Rhaetian and is followed by the Sinemurian.In Europe stratigraphy the Hettangian is a part of the time span in...  and Toarcian	Alum Shale Alum shale Alum shale is a variety of shale or clay slate containing pyrites. Decomposition of pyrite by weathering forms sulfuric acid, which acts on potash and alumina constituents to form alum, often efflorescences on the rock.Alum shale contains kerogen originated from algae... , Yorkshire, England; Holzmaden Holzmaden Holzmaden is a town in Baden-Württemberg, Germany that lies between Stuttgart and Ulm.The ground in and around the city contains rich layers of well preserved fossils of the Jurassic period. The fossils are found in the 160 million year old Posidonia Shale and displayed in the local Museum Hauff... , Baden-Württemberg, Germany	A genus of sauropterygian carnivorous reptile belonging to the pliosaur superfamily, it was about 7m long.

†Sauropods

Sauropoda Sauropoda Sauropoda , or the sauropods , are an infraorder of saurischian dinosaurs. They had long necks, long tails, small heads , and thick, pillar-like legs. They are notable for the enormous sizes attained by some species, and the group includes the largest animals to have ever lived on land...  of the Toarcian
Taxa	Presence	Location	Description	Images
Barapasaurus Barapasaurus Barapasaurus is a genus of sauropod dinosaur from Early Jurassic rocks of India. The specific name for its only species, B. tagorei, means 'Tagore's', which honors Bengali poet, writer, painter, and musician Rabindranath Tagore.-Description:...		India	The earliest known sauropod. Reached a length of about 18 metres (60 feet), and weighed about 48 tones (53 tons). Its height to the hip was approximately 5.5 metres (18 feet)
Rhoetosaurus Rhoetosaurus Rhoetosaurus , named after Rhoetus, a titan in Greek Mythology, is a genus of sauropod dinosaur from the Jurassic of what is now eastern Australia. Rhoetosaurus is estimated to have been about 12–15 metres long...	Disputed	Central Queensland, Australia	Estimated to have been about 12-15 metres long. Has been compared to Shunosaurus, based on similar general age, but without justification.

†Thalattosuchians

Thalattosuchia Thalattosuchia Thalattosuchia is the name given to a clade of marine crocodylomorphs from the Early Jurassic to the Early Cretaceous that had a cosmopolitan distribution. They are sometimes colloquially referred to as marine crocodiles or sea crocodiles, though they are not actually members of Crocodilia.The term...  of the Toarcian
Taxa	Presence	Location	Description	Images
Pelagosaurus Pelagosaurus Pelagosaurus is an extinct genus of thalattosuchian crocodyliform that lived during the Toarcian stage of the Lower Jurassic, around 183 Ma to 175 Ma , in shallow epicontinental seas that covered much of what is now Western Europe...		Somerset, England; France; Germany
Peipehsuchus Peipehsuchus Peipehsuchus is an extinct genus of teleosaurid crocodyliform from the Early Jurassic . The type species, P. teleorhinus, is known from China and fragmentary remains were found in the Callovian of Kyrgyzstan.-References:...
Platysuchus Platysuchus Platysuchus is an extinct genus of teleosaurid crocodyliform from the Early Jurassic . All specimens are known from Germany.- External links:*...
Steneosaurus Steneosaurus Steneosaurus is an extinct genus of teleosaurid crocodyliform from the Early Jurassic to Early Cretaceous . Fossil specimens have been found in England, France, Germany, Switzerland and Morocco.-Species:...

Literature

; 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...

.; 1842: Paléontologie française. 1. Terrains oolitiques ou jurassiques, Bertrand, Paris.

External links

• GeoWhen Database - Toarcian
• Lower Jurassic timescale, at the website of the subcommission for stratigraphic information of the ICS
• Stratigraphic chart of the Lower Jurassic, at the website of Norges Network of offshore records of geology and stratigraphy