| 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 Early Jurassic is the first epoch of the Jurassic period, corresponding to the Lower Jurassic series of the Jurassic system in stratigraphy. It lasted from 201.4 ± 0.2 Ma (million years ago) to 174.7 ± 0.8 Ma (IUGS 2023). It is preceded by the Rhaetian age of the Late Triassic and is followed by the Aalenian age of the Middle Jurassic. In the Early Jurassic, which began with Triassic-Jurassic mass extinction, dinosaurs became the truly dominant land vertebrates, while the ancestors of mammals evolved into small insect-eating animals.
Definition[]
The GSSP of the Lower Jurassic series as well as the Hettangian stage and the whole Jurassic system was ratified in 2010. The beginning of the period is related to the first appearance of the ammonite Psiloceras spelae tirolicum. The type section is located in Tyrol, Austria.[2] Since there were almost no conodonts in the Early Jurassic, ammonites are used as markers of the boundaries of the vast majority of the non-Triassic subdivisions of the Mesozoic.
Subdivisions[]
The Lower Jurassic divided into four stages: Hettangian, Sinemurian, Pliensbachian and Toarcian. In geochronology, all of them correspond to the same ages.
Paleogeography[]
The supercontinent Pangea was in the process of breaking up. Gondwana separated from Laurasia, and many coastal areas were flooded by the waters of the Tethys Ocean. Despite this, there were still close ties between the continents.
Early Jurassic life[]
Many common Late Triassic animals did not survive the T-J mass extinction. Parareptiles, placodonts, nothosaurs, pseudosuchians (except crocodylomorphs), dicynodonts and many large ichthyosaurs became completely extinct. Soon after the extinction, the last conodonts disappeared. The extinction also affected cephalopods: nautiluses almost went extinct.
However, species diversity gradually recovered. In the seas, cephalopods and ichthyosaurs gained numbers again. The number of sauropterygians increased and thalattosuchians, marine relatives of modern crocodiles, appeared. The first gars (Lepisosteiformes) appeared in the Early Jurassic.[3] It is assumed that true sharks also arose during this time. On land, the real flourishing of dinosaurs began. Large herbivores, mainly sauropodomorphs like Massospondylus and Barapasaurus, were hunted by large theropods like Cryolophosaurus, Dilophosaurus and Piatnitzkysaurus. There were also smaller forms like Kayentavenator. Ornithischians were predominantly small, although some, like Scelidosaurus, grew to over 3 m in length. To protect themselves from predators, some of them have acquired dense scales on their backs. The number of pterosaurs increased. Relatives of mammals (and/or mammals themselves) like Oligokyphus were mainly small in this epoch, and most of them known only by the fossil teeth.
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.
- ↑ López-Arbarello, A. (2012). "Phylogenetic Interrelationships of Ginglymodian Fishes (Actinopterygii: Neopterygii)". PLOS ONE. 7 (7): e39370. doi:10.1371/journal.pone.0039370