| System (period) | Series (epoch) | Stage (age) | Lower boundary, Ma | |
|---|---|---|---|---|
| Cretaceous | Lower | Berriasian | ~145 | |
| Jurassic | Upper (Late) | Tithonian | 149.2±0.7 | |
| Kimmeridgian |  154.8±0.8
| |||
| Oxfordian | 161.5±1.0 | |||
| Middle | Callovian | 165.3±1.1 | ||
| Bathonian | 168.2±1.2
| |||
| Bajocian | 170.9±0.8
| |||
| Aalenian | 174.7±0.8
| |||
| Lower (Early) | Toarcian | 184.2±0.3
| ||
| Pliensbachian | 192.9±0.3
| |||
| Sinemurian | 199.5±0.3
| |||
| Hettangian | 201.4±0.2
| |||
| Triassic | Upper | Rhaetian | older | |
| Subdivisions and "golden spikes" according to IUGS as of September 2023[1] | ||||
The Aalenian is a first stage of the Middle Jurassic series, corresponding to the Aalenian age of the Middle Jurassic epoch. It lasted from approximately 174.7 Ma to around 170.9 Ma (million years ago). It is preceded by the Toarcian age of the Early Jurassic and is followed by the Bajocian age of the Middle Jurassic.
Stenopterygius aaleniensis, an ichthyosaur species, is named after this stage from which its specimen was collected.
Definition[]
The GSSP of the Aalenian stage and the whole Middle Jurassic series was ratified in 2000. The lower boundary is fixed in the base of Bed FZ 107, Spain, and related to the first appearance of the ammonites Leioceras opalinum and Leioceras lineatum.[2]
Aalenian life[]
Aalenian fossils are quite rare. Crinoids like Praetetracrinus grew on the seabed, and starfish like Sinosura crawled between their stems. It is known that many ammonites lived in the seas. Aalenian ammonite genera include Praeoppelia, Eudmetoceras, Graphoceras, Docidoceras and Leioceras. Belemnites like Arcobelus from the Lower Aalenian strata of Siberia were also numerous. Several fossils of bivalves, ammonites, a ganoid fish Dapedium, a thalattosuchian Opisuchus and an ichthyosaur Stenopterygius were found in the Aalenian Opalinuston Formation in Heiningen, Germany. The species Stenopterygius aaleniensis is named after this stage in 2012. Two isolated teeth belonging to teleosaurid, possibly Steneosaurus, were collected from the Aalenian of Western Carpathians, Slovakia.[3] Aalenian plesiosaurs are also rare. One very incomplete specimen, probably elasmosaurid, was described from the Aalenian sediments of Western France in 2007.[4]
On land, dinosaur evolution continued. Sauropodomorphs were the largest herbovires of the time. "Alan the Dinosaur", the oldest sauropod found in the United Kingdom, was found in the Aalenian sediments. Nebulasaurus lived in what is now Xiabanjing, China, around the same time.
References[]
- ↑ "Latest version of international chronostratigraphic chart". International Commission on Stratigraphy. https://stratigraphy.org/chart#latest-version.
- ↑ "GSSP Table - Mesozoic Era". https://timescalefoundation.org/gssp/index.php?parentid=35.
- ↑ Andrej Čerňanský, Ján Schlögl, Tomáš Mlynský & Štefan Józsa (2017). "First evidence of the Jurassic thalattosuchian (both teleosaurid and metriorhynchid) crocodylomorphs from Slovakia (Western Carpathians)". Historical Biology 31 (18). DOI:10.1080/08912963.2017.1414212 ISSN: 0891-2963 (Print) 1029-2381 (Online)
- ↑ Peggy Vincent, Nathalie Bardet, Paris, and Nicolas Morel, Le Mans (2007). "An elasmosaurid plesiosaur from the Aalenian (Middle Jurassic) of Western France". Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen 243 (3): 363-370. DOI:10.1127/0077-7749/2007/0243-0363