Toarcian

The Toarcian is, in the ICS' geologic timescale, an age and stage in the Early or Lower Jurassic. It spans the time between 182.7 Ma (million years ago) and 174.1 Ma.[2] It follows the Pliensbachian and is followed by the Aalenian.[3]

System/ Period	Series/ Epoch	Stage/ Age	Age (Ma)
Cretaceous	Lower/ Early	Berriasian	younger
Jurassic	Upper/ Late	Tithonian	~145.0	152.1
		Kimmeridgian	152.1	157.3
		Oxfordian	157.3	163.5
	Middle	Callovian	163.5	166.1
		Bathonian	166.1	168.3
		Bajocian	168.3	170.3
		Aalenian	170.3	174.1
	Lower/ Early	Toarcian	174.1	182.7
		Pliensbachian	182.7	190.8
		Sinemurian	190.8	199.3
		Hettangian	199.3	201.3
Triassic	Upper/ Late	Rhaetian	older
Subdivision of the Jurassic system according to the ICS, as of 2020.[1]

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

Amphibians

Amphibians of the Toarcian
Taxa	Presence	Location	Description	Images
Siderops	Pliensbachian-Toarcian	Evergreen Formation, Australia	A brachyopoid stereospondyl.	Siderops Notobatrachus
Notobatrachus N. reigi	Upper Toarcian	Cañadón Asfalto Formation, Chubut, Argentina	An extinct genus of archaeobatrachian frog and a member of the extant family Ascaphidae. One of the oldest true frogs discovered.

†Ichthyosaurs

Ichthyosaurs of the Toarcian
Taxa	Presence	Location	Description	Images
Stenopterygius		Europe
Temnodontosaurus	Hettangian to Toarcian	All over Europe	An ichthyosaur that exceeded 12 metres (39 ft) in length

†Ornithischians

Ornithischians of the Toarcian
Taxa	Presence	Location	Description	Images
Emausaurus		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 of the Toarcian
Taxa	Presence	Location	Description	Images
Bishanopliosaurus		Ziliujing Formation, China	A pliosauroid, possibly a rhomaleosaurid.	Bishanopliosaurus Hydrorion Meyerasaurus Microcleidus Rhomaleosaurus Seeleysaurus
Hauffiosaurus		England and Germany	A basal pliosaurid.
Hydrorion		Posidonia Shale formation, Germany	A basal plesiosauroid.
Lusonectes		Portugal	A basal plesiosauroid, likely a close relative of Microcleidus.
Meyerasaurus		Holzmaden,southwestern Germany	A rhomaleosaurid. Its skull has a length of 37 cm, and the animal was about 3.35 m (11.0 ft) in length.
Microcleidus M. homalospondylus M. macropterus M. tournemirensis M. melusinae		Tournemire, Aveyron, France	A plesiosaur similar to Elasmosaurus, measuring around 3 meters in length. A fossil of a single but nearly complete skeleton of an animal approximately 4 meters (13 ft) long, originally described as Occitanosaurus tournemirensis, is now considered as a species of Microcleidus..
Plesiopterys		Posidonia Shale formation, Germany	A basal plesiosauroid, possibly a close relative of Cryptoclidus.
Rhomaleosaurus	Toarcian	Alum Shale, Yorkshire, England	A genus of sauropterygian carnivorous reptile belonging to the pliosaur superfamily, it was about 7m long.
Seeleyosaurus	Toarcian	Württemberg, Germany	A large (about 3 to 5 meters long), microcleidid, 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
Sthenarosaurus		England	A genus of rhomaleosaurid pliosaur.

†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.[4]

†Thalattosuchians

Thalattosuchia of the Toarcian
Taxa	Presence	Location	Description	Images
Mystriosaurus		England; and Germany	A teleosaurid.	Pelagosaurus Platysuchus Steneosaurus
Peipehsuchus		China	A teleosaurid.
Pelagosaurus		Somerset, England; France; Germany	Traditionally placed in Teleosauridae, it might a basal member of Metriorhynchoidea instead.
Platysuchus		Germany	A teleosaurid.
Steneosaurus		Germany; France; England; Morocco; and Switzerland	A teleosaurid.

Theropods

Theropods of the Aalenian
Taxa	Presence	Location	Description	Images
Asfaltovenator	Toarcian-Bajocian	Cañadón Asfalto Basin, Patagonia, Argentina	A large basal carnosaur. The unique combination of characteristics seen in Asfaltovenator may indicate megalosauroids and allosauroids shared a common ancestor not shared with Coelurosauria.
Berberosaurus	Middle Toarcian	Azilal Formation in the High Atlas of Toundoute, Ouarzazate, Morocco.	A primitive, medium sized neotheropod, possibly a dilophosaurid but most likely a basal ceratosaur.	Berberosaurus.
Condorraptor	Aalenian-Bajocian	Cañadón Asfalto Basin, Patagonia, Argentina	It was among the earliest large South American theropods.	Condorraptor.
Magnosaurus	Aalenian-Bajocian	Dorset, England	Magnosaurus was one of the first megalosaurids to evolve.	Magnosaurus.

References

1. http://www.stratigraphy.org/index.php/ics-chart-timescale
2. Benton, Michael J. (2012). Prehistoric Life. Edinburgh, Scotland: Dorling Kindersley. pp. 44–45. ISBN 978-0-7566-9910-9.
3. For a detailed geologic timescale see Gradstein et al. (2004)
4. Allain, Ronan; Najat Aquesbi; Jean Dejax; Christian Meyer; Michel Monbaron; Christian Montenat; Philippe Richir; Mohammed Rochdy; Dale Russell; Philippe Taquet (2004). "A basal sauropod dinosaur from the Early Jurassic of Morocco" (PDF). Comptes Rendus Palevol. 3 (3): 199–208. doi:10.1016/j.crpv.2004.03.001. ISSN 1631-0683.

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. (in 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