Toarcian

The Toarcian is, in the ICS' geologic timescale, an age or stage in the Early or Lower Jurassic. It spans the time between 182.7 Ma (million years ago) and 174.1 Ma.^[1] It follows the Pliensbachian and is followed by the Aalenian.^[2]

The Toarcian age began with the Toarcian turnover, the extinction event that sets its fossil faunas apart from the previous Pliensbachian age.

Stratigraphic definitions

The Toarcian takes its name from the city of Thouars, just south of Saumur in the Loire Valley of France. The stage was introduced by French palaeontologist Alcide d'Orbigny in 1842, after examining rock strata of this age in a quarry near Thouars.

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

The base of the Toarcian is defined as the place in the stratigraphic record where the ammonite genus Eodactylites first appears. A global reference profile (a GSSP) for the base is located at Peniche, Portugal. The top of the stage is at the first appearance of ammonite genus Leioceras.

In the Tethys domain, the Toarcian contains the following ammonite biozones:

• zone of Pleydellia aalensis
• zone of Dumortieria pseudoradiosa
• zone of Phlyseogrammoceras dispansum
• zone of Grammoceras thouarcense
• zone of Haugia variabilis
• zone of Hildoceras bifrons
• zone of Harpoceras serpentinum
• zone of Dactylioceras tenuicostatum

Palaeontology

†Ornithischians

†Plesiosaurs

Plesiosauria of the Toarcian
Taxa	Presence	Location	Description	Images
Microcleidus		Tournemire, 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	Rhomaleosaurus
Seeleyosaurus	Toarcian	Württemberg, 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	Toarcian	Alum Shale, Yorkshire, England	A genus of sauropterygian carnivorous reptile belonging to the pliosaur superfamily, it was about 7m long.

†Sauropods

Sauropoda of the Toarcian
Taxa	Presence	Location	Description	Images
Barapasaurus		Maharastra, India	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)	Barapasaurus
Rhoetosaurus	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.
Tazoudasaurus	Toarcian	Ouarzazate province, Morocco	Small primitive sauropod, about 9 metres long. Member of Vulcanodontidae family.[3]

†Thalattosuchians

Thalattosuchia of the Toarcian
Taxa	Presence	Location	Description	Images
Pelagosaurus		Somerset, England; France; Germany		Pelagosaurus Platysuchus Steneosaurus
Peipehsuchus
Platysuchus		Germany
Steneosaurus		Germany; France; England; Morocco; and Switzerland

References

Sources

• Gradstein, F.M.; Ogg, J.G. & Smith, A.G.; 2004: A Geologic Time Scale 2004, Cambridge University Press.
• d´Orbigny, A.C.V.M.D.; 1842: Paléontologie française. 1. Terrains oolitiques ou jurassiques, Bertrand, Paris. (French)

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