| 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 Callovian is a fourth and upper stage of the Middle Jurassic series, corresponding to the Callovian age of the Middle Jurassic epoch. It lasted from approximately 165.3 Ma to around 161.5 Ma (million years ago). It succeeds the Bathonian age and precedes the Oxfordian age of the next epoch, the Late Jurassic.
Definition[]
As of 2024, there is no GSSP defining the base of the Callovian stage. The possible candidates are sections in Pfeffingen (Swabian Alb, Germany) and in Russia. The First Appearing Datum (FAD) of the ammonite genus Kepplerites is suggested as the marker of the lower boundary of this stage. Kepplerites is related to the base of Macrocephalites herveyi Zone in sub-Boreal province of the United Kingdom to southwest Germany.[2]
Callovian life[]
The active evolution of marine life continued. The seas that covered the territory of present-day Europe were inhabited by numerous fish and marine reptiles that fed on them. In the Callovian strata of Oxford Clay Formation in the United Kingdom, such fauna is present. The seabed was inhabited by brittle stars (ophiuroids) Ophiotitanous and Ophioplax, and various fish swam above them. Caturus, Lepidotus, Pholidophorus, Leptolepis and Aspidorhynchus are assigned to different orders but all of them are members of the group Actinopteri, the largest part of the ray-finned fish. Long-necked plesiosaurs Colymbosaurus hunted these fish, and they themselves became prey for short-necked relatives, Liopleurodon and Peloneustes.
An example of a Callovian dinosaur Omeisaurus.
At this time, temnospondyls like Ferganobatrachus still existed, although their diversity had decreased significantly compared to the late Paleozoic and the Triassic. Crocodylomorphs like Sunosuchus or marine Peipehsuchus continued to displace them. All three of the above animals were found in the Callovian lagoonal strata of Balabansai Formation in Kyrgyzstan where other typical representatives of the fauna have also been discovered. Polyacrodus, a hybodontiform shark, Ferganoceratodus, a dipnoan fish, and turtles like Toxocheloides, Plesiochelys, Chengyuchelys and Xinjiangchelys, lived in water. Tashkumyrodon is a member of docodonts, the large mammaliaform group whose representatives have already occupied a variety of ecological niches: from inhabitants of reservoirs to arboreal insect hunters. Ferganocephale is a member of ornithischian dinosaurs which, for the most part, remained small and fast moving herbivores, although more specialized forms had already appeared in other parts of the world. The early stegosaurids like Lexovisaurus and Loricatosaurus acquired spines to protect them from predators and soon spread widely. However, the most successful herbivores were still the sauropods like Shunosaurus and Omeisaurus. Due to their long necks, they could eat both low-growing vegetation and pluck high-lying tree branches. Tetanurans like Yangchuanosaurus and Monolophosaurus were the dominant land predators of the Callovian.
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.