|Subdivision of the Jurassic system according to the IUGS, as of July 2012.|
The Hettangian is the earliest age or lowest stage of the Jurassic period of the geologic timescale. It spans the time between 201.3 ± 0.2 Ma and 199.3 ± 0.3 Ma (million years ago). The Hettangian follows the Rhaetian (part of the Triassic period) and is followed by the Sinemurian.
In Europe stratigraphy the Hettangian is a part of the time span in which the Lias was deposited. An example is the British Blue Lias, which has an upper Rhaetian to Sinemurian age. Another example is the lower Lias from the northern calcarious alps where have been found well preserved but very rare ammonites like e.g. Alsatites.
Stratigraphic definitions 
The Hettangian was introduced in the literature by Swiss palaeontologist, Eugène Renevier, in 1864. The stage takes its name from Hettange-Grande, a town in north-eastern France, just south of the border with Luxembourg on the main road from Luxembourg City to Metz.
The base of the Hettangian stage (which is also the base of the Lower Jurassic series and the entire Jurassic system) is defined as the place in the stratigraphic column where fossils of the ammonite genus Psiloceras first appear. A global reference profile (a GSSP) for the base was defined 2010 at the Kuhjoch in the Karwendel in western Austria. The top of the Hettangian stage (the base of the Sinemurian) is at the first appearances of ammonite genera Vermiceras and Metophioceras.
At the end of the Triassic period, the Ammonites died out almost entirely by external events.
In Hettangian however, the "Neoammoniten" developed relatively quickly, so that even in the middle Hettangian a large number of genera and species exists again. In contrast to later periods obviously the conditions for fossilisation were not optimal, therefore only a few sites with well-preserved hettangian ammonites are known.
|Ichthyosauria of the Hettangian|
|From Hettangian to Sinemurian||Belgium, England, Germany||Among the best known ichthyosaur genera, was smaller than most of its relatives, measuring 2 m (6 ft 6 inches) in length.|
|From Hettangian to Toarcian||England, Germany||The first Ichthyosaur, T.platyodon discovered by Mary Anning from the Blue Lias at Lyme Regis. Species of Temnodontosaurus were large, exceeding 12 meters (40 ft) in length.|
|Mammaliaformes of the Hettangian|
|Ornithischians of the Hettangian|
|From Hettangian to Sinemurian||Upper Elliot Formation, Lesotho and Cape Province, South Africa||Considered the most basal member of the family Heterodontosauridae|
|From Hettangian to Sinemurian||Lesotho||As the only fossil known of it is a partial jawbone with three teeth, Fabrosaurus is a nomen dubium and may in fact be the same as Lesothosaurus.|
|Upper Elliot Formation, Cape Province, South Africa||A small, fleet-footed ornithischian that reached a maximum size of about 3 feet. The hand of Heterodontosaurus had five fingers, two of which seem to be opposable, allowing Heterodontosaurus to grasp and manipulate food.
Another interesting feature is the specialization of teeth which gave rise to the animal's name. At the front of the jaw beside the beak were small teeth likely used for chopping off leaves and stems.
|From Hettangian to Sinemurian||Upper Elliot Formation, Orange Free State, South Africa||A heterodontosaurid ornithischian|
|From Hettangian to Sinemurian||Upper Elliot Formation, Cape Province, South Africa||A small herbivore dinosaur despite long canines it sported in its jaws; due to this unique characteristic it is very clearly allied to Heterodontosaurus|
|From Hettangian to Sinemurian||Charmouth, West Dorset, England; Kayenta Formation, Arizona, USA||A genus of quadrupedal, lightly plated, herbivorous dinosaur about 4 meters long (13 ft)|
|Arizona, USA||A bipedal armored herbivore, was around 1.3 m (4 ft 4 inches) long, 0.5 m (18 in) tall at the hips, and weighed 10 kg (22 lb).|
|From Hettangian to Sinemurian||Stormberg Series Formations, South Africa, Lesotho||A primitive ornithischian, about 2 meters long. The proportions of the posterior limbs show differences with those of Lesothosaurus, and reveal a lower ability to run|
|Plesiosauria of the Hettangian|
|Hettangian to Toarcian||Harbury, Warwickshire, UK|
|Hettangian and Toarcian||Barrow-upon-Soar, Leicestershire, England||A genus of sauropterygian carnivorous reptile belonging to the pliosaur superfamily, it was about 7m long.|
See also 
- For a detailed geologic timescale, see Gradstein et al. (2004)
- GSSP Table
- Gradstein, F.M.; Ogg, J.G. & Smith, A.G.; 2004: A Geologic Time Scale 2004, Cambridge University Press.
- Renevier, E.: Notices géologiques et paléontologiques sur les Alpes Vaudoises, et les régions environnantes. I. Infralias et Zone à Avicula contorta (Étage Rhaetien) des Alpes Vaudoises Bulletin de la Société Vaudoise des Sciences Naturelles 8, p. 39-97. (French)
- GeoWhen Database - Hettangian
- 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
|Lower/Early Jurassic||Middle Jurassic||Upper/Late Jurassic|
|Hettangian | Sinemurian
Pliensbachian | Toarcian
|Aalenian | Bajocian
Bathonian | Callovian
|Oxfordian | Kimmeridgian
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