Callovian

In the geologic timescale, the Callovian is an age or stage in the Middle Jurassic, lasting between 166.1 ± 4.0 Ma (million years ago) and 163.5 ± 4.0 Ma. It is the last stage of the Middle Jurassic, following the Bathonian and preceding the Oxfordian.^[1]

Stratigraphic definitions

The Callovian stage was first described by French palaeontologist Alcide d'Orbigny in 1852. Its name derives from the latinized name for Kellaways Bridge, a small hamlet 3 km north-east of Chippenham, Wiltshire, England.

The base of the Callovian is defined as the place in the stratigraphic column where the ammonite genus Kepplerites first appears, which is the base of the biozone of Macrocephalites herveyi. A global reference profile (a GSSP) for the base had in 2009 not yet been assigned.

The top of the Callovian (the base of the Oxfordian) is at the first appearance of ammonite species Brightia thuouxensis.

Subdivision

Matmor Formation (Callovian, Peltoceras athleta Zone) in Makhtesh Gadol, Israel.

The Callovian is often subdivided into three substages (or subages): Lower/Early, Middle and Upper/Late Callovian. In the Tethys domain, the Callovian encompasses six ammonite biozones:

• zone of Quenstedtoceras lamberti
• zone of Peltoceras athleta
• zone of Erymnoceras coronatum
• zone of Reineckeia anceps
• zone of Macrocephalites gracilis
• zone of Bullatimorphites bullatus

Palaeogeography

During the Callovian, Europe was an Archipelago of a dozen or so large islands. Between them were extensive areas of continental shelf. Consequently, there are shallow marine Callovian deposits in Russia and from Belarus, through Poland and Germany, into France and eastern Spain and much of England. Around the former island coasts are frequently, land-derived sediments. These are to be found, for example, in western Scotland.^[2]

The Louann Salt and the southern Campeche Salt of the Gulf of Mexico are thought to have formed by an embayment of the Pacific Ocean across modern-day Mexico.^[3]

Palaeontology

Crocodylomorphs

Crocodylomorphs of the Callovian
Taxa	Presence	Location	Description	Images
Junggarsuchus			The sphenosuchian Junggarsuchus was a small, ~1 meter long, Chinese predator.	A life restoration of a Metriorhynchus species.
Metriorhynchus			An opportunistic carnivore that fed on fish, belemnites and other marine animals and possible carrion. Metriorhynchus grew to an average adult length of 3 meters (9.6 ft), although some individuals may have reached lengths rivaling those of large nile crocodiles.
Steneosaurus

†Ornithischians

Ornithischia of the Callovian
Taxa	Presence	Location	Description	Images
Agilisaurus		Dashanpu Formation, Sichuan, China	A 4-foot-long (1.2 m) bipedal herbivore that was built for speed. It was discovered in one of China's many Callovian deposits.	Agilisaurus
Callovosaurus		England	A dryosaurid iguanodont, estimated to have been 3.5 meters long
Ferganocephale		Kyrgyzstan	Possibly an early pachycephalosaurid
Hexinlusaurus	Bathonian to Callovian	Lower Shaximiao Formation, Sichuan, China	A basal neornithischian

†Plesiosaurs

Plesiosaurs of the Callovian
Taxa	Presence	Location	Description	Images
Liopleurodon				Liopleurodon was a large pliosaur from the Callovian stage.
Pachycostasaurus
Peloneustes				Peloneustes
Simolestes				Simolestes vorax

†Sauropods

†Stegosauria

Stegosaurs of the Callovian
Taxa	Presence	Location	Description	Images
Huayangosaurus	Bathonian to Callovian	Lower Shaximiao Formation, Sichuan, China	A 4.5 meters in length quadrupedal herbivore with a small skull and a spiked tail. Bore the distinctive double row of plates, rising vertically along its arched back, of all the stegosaurians and two pairs of long spikes extending horizontally near the end of its tail	Huayangosaurus
Lexovisaurus		England	Traditionally, Lexovisaurus was depicted as having either large spines over the hips or shoulders, with a selection of flat plates and round pointed spines that ran along the back and tail. It was probably about 5 m long.
Loricatosaurus		France; England	Known from remains previously assigned to Lexovisaurus.

Theropods

Theropods of the Callovian
Taxa	Presence	Location	Description	Images
Eustreptospondylus			A moderately large (17–23 feet long) predatory dinosaur that was closely related to Megalosaurus.	Eustreptospondylus.
Gasosaurus			An 11–13 foot predator from China whose discovery was assisted by the petroleum industry.
Pedopenna
Yangchuanosaurus			A Chinese theropod. One specimen was at one time informally called "Szechuanoraptor".

†Ammonitida

Members of the Order Ammonitida are known as ammonitic ammonites. They are distinguished primarily by their suture lines. In ammonitic suture patterns, the lobes and saddles are much subdivided (fluted) and subdivisions are usually rounded instead of saw-toothed. Ammonoids of this type are the most important species from a biostratigraphical point of view. This suture type is characteristic of Jurassic and Cretaceous ammonoids but extends back all the way to the Permian.

Ammonites of the Callovian
Taxa	Presence	Location	Description	Images
Cadomites				Peltoceras solidum ammonite from the Matmor Formation (Jurassic, Callovian) in Makhtesh Gadol, Israel.
Oecoptychius
Oecotraustes
Oxycerites
Peltoceras

†Belemnites

Belemnites of the Callovian
Taxa	Presence	Location	Description	Images
Produvalia				Callovian belemnite from the Zohar Formation, northern Israel

Nautiloids

Nautiloids of the Callovian
Taxa	Presence	Location	Description	Images
Somalinautilus				An illustration of a variety of fossil nautiloids.

Neocoleoids

Neocoleoidea of the Callovian
Taxa	Presence	Location	Description	Images
Proteroctopus Proteroctopus ribeti
Rhomboteuthis Rhomboteuthis lehmani				Pyritized fossil ofRhomboteuthis lehmanifrom Voulte-sur-Rhône, France.
Vampyronassa Vampyronassa rhodanica				Pyritized fossil of Vampyronassa rhodanica from Voulte-sur-Rhône, France.

References

Notes

Literature

• Elmi, S. & Babin, C.; 2002: Histoire de la Terre, Dunod, Paris (2nd ed.), ISBN 2-10-006631-5. (French)
• 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. 642 p, Bertrand, Paris. (French)

External links

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