Aalenian
From Wikipedia, the free encyclopedia
The Aalenian (pronounced /ɑːˈliːniən/) is a subdivision of the Middle Jurassic epoch of the geologic timescale that extends from about 175.6 Ma to about 171.6 Ma (million years ago). It was preceded by the Toarcian era and succeeded by the Bajocian.
The stage takes its name from the town of Aalen, some 100 km east of Stuttgart in Germany. The town lies at the southwestern end of the Frankischer Jura.
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[edit] Invertebrate Fauna
[edit] Ammonites
Ammonites are an extinct group of marine animals of the subclass Ammonoidea in the class Cephalopoda. Ammonites' closest living relative is probably not the modern Nautilus (which they outwardly resemble), but rather the subclass Coleoidea (octopus, squid, and cuttlefish). Their fossil shells usually take the form of planispirals, although there were some helically-spiraled and non-spiraled forms (known as "heteromorphs").
[edit] Order 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.
- Abbasites platystomus
- The only known species in this Alaskan genus. Abbasites is believed to be ancestral to the ammonite family Otoitidae.
- Ancolioceras Image:Douvilleiceras Hoplites.jpgLife restorations of two different ammonite genera.
- Asthenoceras
- Bradfordia
- Brasilia
- Bredyia
- Canavarella
- Constileioceras
- Costileioceras
- Cylioceras
- Euaptetoceras
- Eudmetoceras
- Euhoploceras
- Fontannesia
- Graphoceras
- Haplopleuroceras
- Hyperlioceras
- Leioceras
- Ludwigia
- Synonymous with a modern plant genus.
- Malladaites
- Padragosiceras
- Parammatoceras
- Planammatoceras
- Praestrigites
- Pseudammatoceras
- Puchenquia
- Reynesella Image:1212amma.jpgA fossil ammonite of the order ammonitida
- Sonninia
- Spinammatoceras
- Staufenia
- Stephanoceras
- Trilobiticeras
- Tugurites
[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.
The following is a list of belemnite genera whose fossils are geochronologically found first in Aalenian strata. These genera may survive into later geological stages. This list should not be thought of in terms of the lifespan of the genera included.- Belemnopsis
- Holcobelus
- Homaloteuthis
- Megateuthis
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- This Eurasian species was the largest known Belemnite and could grow to lengths of up to 10 feet.
- Pachyteuthis
- Paramegateuthis
- Rhabdobelus
- Sachsibelus
| Jurassic period | ||
|---|---|---|
| Lower/Early Jurassic | Middle Jurassic | Upper/Late Jurassic |
| Hettangian | Sinemurian Pliensbachian | Toarcian | Aalenian | Bajocian Bathonian | Callovian | Oxfordian | Kimmeridgian Tithonian |
de:Aalenium et:Aaleni lade es:Aleniano fr:Aalénien nl:Aalenien pl:Aalen (geologia) pt:Aaleniano ro:Aalenian ru:Ааленский ярус sh:Aalenij uk:Ааленський ярус
