| 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 Kimmeridgian is a second stage of the Upper Jurassic series, corresponding to the Kimmeridgian age of the Late Jurassic epoch.
It lasted from approximately 154.8 Ma to around 149.2 Ma (million years ago). It is preceded by the Oxfordian and is followed by the Tithonian.
Definition[]
The GSSP of the Kimmeridgian stage was ratified in 2021. The lower boundary is fixed in the section on Isle of Skye, Scotland, and related to the first appearance of the ammonites Pictonia flodigarriensis, Prorasenia bowerbanki and Pictonia (Triozites).[2]
Kimmeridgian life[]
Kimmeridgian seas were dominated by reptiles. Ichthyosaurs like Ophthalmosaurus have adapted to diving to great depths. Crocodylomorphs like Steneosaurus hunted in surface waters. The largest predators of that time were short-necked pliosaurids like Pliosaurus.
Allosaurus and Stegosaurus skeletons
This age marks the peak of the evolution of some of the Jurassic dinosaurian groups. Many typical animals of this time are represented in the Morrison Formation, USA. A variety of herbivorous dinosaurs lived on the plains and fed on numerous ferns, cycads and gymnosperms. Small ornithischians like Dryosaurus and Nanosaurus had no obvious defenses, and probably only escaped predators by running fast. Stegosaurids like Stegosaurus could protect themselves with spikes and plates on their backs. Numerous sauropods lived in herds. Such giant animals as Diplodocus, Supersaurus, Apatosaurus, Barosaurus, Galeamopus, Saurophaganax, Camarasaurus, due to to their long necks, plucked lower and upper plants, while Brachiosaurus and its relatives adapted to plucking the tops of trees. The abundance of herbivores led to an increase in predators. Small Ornitholestes, Coelurus and Tanycolagreus hunted mainly for small and mobile prey. Ceratosaurus and Allosaurus could attack larger and more dangerous animals. Largest carnivores like Torvosaurus could have hunted even sauropods like Diplodocus and Camarasaurus. Among pterosaurs, long-tailed forms like Harpactognathus predominated. Many mammals of that time like Docodon and Fruitafossor were small and hunted mainly insects. The pronounced features of an insect eater in the Fruitafossor indicate that in the Kimmeridgian social insects (likely termites) already existed, building large colony nests.
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.