Middle Jurassic
| Eon | Era | Period | Epoch | Start Million years ago |
|---|---|---|---|---|
| Phanerozoic | Cainozoic | Palaeogene | Palaeocene | 66 |
| Mesozoic | Cretaceous | Upper Cretaceous | 100.5 | |
| Lower Cretaceous | 145 | |||
| Jurassic | Upper Jurassic | 163.5 | ||
| Middle Jurassic | 174.1 | |||
| Lower Jurassic | 201.3 | |||
| Triassic | Upper Triassic | 237 | ||
| Middle Triassic | 247.2 | |||
| Lower Triassic | 252.17 | |||
| Palaeozoic | Permian | 298.9 | ||
The Middle Jurassic is the second epoch of the Jurassic period. It lasted from about 174 to 163.5 million years ago (mya).[1]
In the Middle Jurassic, Pangaea began to split apart. It began to separate into Laurasia and Gondwana, and the Atlantic Ocean formed. Tectonic activities closed the Paleo-Tethys Ocean.[2] A subduction zone[3] on the coast of western North America continues to create the ancestral Rocky Mountains.
Contents |
Life of the epoch [change]
Marine life [change]
During this time, marine life (including ammonites and bivalves) flourished. Ichthyosaurs, although common, are reduced in diversity. A type of crocodilians first appeared.
Plesiosaurs became common at this time. The top marine predators, the pliosaurs, grew to the size of killer whales and larger e.g. Pliosaurus, Liopleurodon.
Terrestrial life [change]
New types of dinosaurs evolved on land. Cetiosaurus was an early sauropod found in England in the mid-19th century.[4][5]
The environment in which Cetiosaurus lived was floodplain and open woodland. Brachiosaurs, Megalosaurus and Hypsilophodon also lived in this environment.
The cynodont therapsids flourished with the dinosaurs, but they were only shrew-sized. None grew larger than a badger. One group of cynodonts, the Trithelodonts were becoming rare and eventually became extinct at the end of this epoch. The Tritylodonts were still common, though. In this epoch "true" mammals evolved from a group of cynodonts.
Flora [change]
Conifers were dominant in the Middle Jurassic. Other plants, such as ginkgoes, cycads, and ferns were also common. These are the trees which the large herbivores ate.
Related pages [change]
References [change]
- ↑ International Chronostratigraphic Chart. [1]
- ↑ The Tethys Ocean: an ancient seaway approximately in the position of the Mediterranean.
- ↑ Formed by an oceanic plate sliding under a continental plate.
- ↑ "Cetiosaurus." In: Dodson, Peter et al. The Age of Dinosaurs. Publications International, p65. ISBN 0-7853-0443-6.
- ↑ Upchurch P & Martin J (2002). "The Rutland Cetiosaurus: the anatomy and relationships of a Middle Jurassic British sauropod dinosaur.". Palaeontology 45 (6): 1049–1074. doi:10.1111/1475-4983.00275.
| Precambrian (4.567 gya – 541 mya) | |
|---|---|
| In the left column are Eons, bold are Eras, not bold are Periods. gya = billion years ago, mya = million years ago | |
| Hadean (4.567 gya – 4 gya) | |
| Archaean (4 gya – 2.5 gya) | |
| Proterozoic (4 gya – 2.5 gya) | Palaeoproterozoic (2.5 gya – 1.6 gya)
Mesoproterozoic (1.6 gya – 1 gya) Neoproterozoic (1 gya - 541 mya) Tonian (1 gya – 850 mya) Cryogenian (850 mya – 635 mya) Ediacaran (635 mya – 541 mya) |
| Source | International Chronostratigraphic Chart 2013. International Commission on Stratigraphy, retrieved 8 April 2013. Divisions of geologic time – major chronostratigraphic and geochronologic units USGS, retrieved 8 April 2013. |
