Kimmeridgian
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The Kimmeridgian is a stage of the Late Jurassic Epoch. It spans the time between 155.7 ± 4 Ma and 150.8 ± 4 Ma (million years ago). The Kimmeridgian stage follows the Oxfordian stage and precedes the Tithonian stage.
The stage takes its name from the village of Kimmeridge on the Dorset coast, England where the exposure is at its greatest extent. The beach at Kimmeridge Bay is a good place for looking for fossils — there are specimens on the beach washed in by the tide.
The Kimmeridge Clay formation is the source for about 95% of the petroleum in the North Sea.
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[edit] Usage of the term
Historically the term Kimmeridgian has been used in two different ways. The base of the interval is the same but the top was defined by British stratigraphers as the base of the Portlandian stage (sensu anglico) whereas in France the top was defined as the base of the Tithonian (sensu gallico). The differences have not yet been fully resolved, although Kimmeridge-Tithonian are now the agreed terms globally[1]
[edit] Vertebrate Fauna
[edit] Birds
Birds (class Aves) are bipedal, warm-blooded, egg-laying vertebrate animals. Birds evolved from theropod dinosaurs during the Jurassic period, c 200 to 150 Ma (million years ago), and the earliest known bird is the Late Jurassic Archaeopteryx, c 155–150 Ma. Modern birds are characterised by feathers, a beak with no teeth, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a lightweight but strong skeleton. All birds have forelimbs modified as wings and most can fly, though some species have lost the ability to fly.
- Archaeopteryx lithographica
[edit] Dinosaurs
Dinosaurs were vertebrate animals that dominated terrestrial ecosystems for over 160 million years, first appearing approximately 230 million years ago. At the end of the Cretaceous Period, 65 million years ago, a catastrophic extinction event ended the dominance of dinosaurs on land.
- Amphicoelias
- Aviatyrannis jurassica
- Dystrophaeus
- Europasaurus holgeri
- Stokesosaurus clevelandi
[edit] Thalattosuchians
Thalattosuchia is the name given to a clade of marine crocodylomorphs from the Early Jurassic to the Early Cretaceous that had a cosmopolitan distribution.
- Dakosaurus maximus, type species of the genus, is known from Western Europe (England, France, Switzerland and Germany) of the Late Jurassic (Late Kimmeridgian-Early Tithonian).
- 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 feet), although some individuals may have reached lengths rivaling those of large nile crocodiles.
[edit] Invertebrate Fauna
[edit] Ammonitida
Members of the order ammonitda 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.
[edit] Genera Surving From the Bajocian
The following genera of Ammonites first appear in Bajocian rocks, but survived to this article's eponymous stage.
- Somalinautilus
[edit] Belemnites
Belemnites (or belemnoids) are an extinct group of marine cephalopod, very similar in many ways to the modern squid and closely related to the modern cuttlefish. Like them, the belemnites possessed an ink sac, but, unlike the squid, they possessed ten arms of roughly equal length and no tentacles.
[edit] Genera Surviving From the Bajocian
The following genera of Belemnites first appear in Bajocian rocks, but survived to this article's eponymous stage.
- Produvalia
[edit] Environment
The variation of fauna during the Kimmeridgian stage indicates the existence of two distinct environments, the first being a being a shallow and agitated layer abundant in pebbles and fossils and the second following environment being a calm and deep layer marked by an absence of pebbles and by an abundance of pelagic organisms, such as Ammonites.
[edit] Localities
[edit] References
- ^ SUBCOMMISSION ON JURASSIC STRATIGRAPHY, Newsletter 31, Edited by Nicol Morton and Paul Bown, August 2004
| Jurassic period | ||
|---|---|---|
| Lower/Early Jurassic | Middle Jurassic | Upper/Late Jurassic |
| Hettangian | Sinemurian Pliensbachian | Toarcian | Aalenian | Bajocian Bathonian | Callovian | Oxfordian | Kimmeridgian Tithonian |
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