Middle Jurassic

The Middle Jurassic is the second epoch of the Jurassic Period. It lasted from about 174 to 163 million years ago. Fossil-bearing rocks from the Middle Jurassic are relatively rare, but some important formations include the Forest Marble Formation in England, the Kilmaluag Formation in Scotland,[2] the Daohugou Beds in China, Itat Formation in Russia, and the Isalo III Formation of western Madagascar.

System/
Period
Series/
Epoch
Stage/
Age
Age (Ma)
Cretaceous Lower/
Early
Berriasian younger
Jurassic Upper/
Late
Tithonian ~145.0 152.1
Kimmeridgian 152.1 157.3
Oxfordian 157.3 163.5
Middle Callovian 163.5 166.1
Bathonian 166.1 168.3
Bajocian 168.3 170.3
Aalenian 170.3 174.1
Lower/
Early
Toarcian 174.1 182.7
Pliensbachian 182.7 190.8
Sinemurian 190.8 199.3
Hettangian 199.3 201.3
Triassic Upper/
Late
Rhaetian older
Subdivision of the Jurassic system
according to the ICS, as of 2017.[1]

Paleogeography

MiddleJurassicMap
Map of the Middle Jurassic

During the Middle Jurassic epoch, Pangaea began to separate into Laurasia and Gondwana, and the Atlantic Ocean formed. Tectonic activities are active on eastern Laurasia as the Cimmerian plate continues to collide with Laurasia's southern coast, completely closing the Paleo-Tethys Ocean. A subduction zone on the coast of western North America continues to create the Ancestral Rocky Mountains.

Middle Jurassic fauna

The Middle Jurassic is one of the key periods in the evolution of life on earth. Many groups, including dinosaurs and mammals, diversified during this time.[3][4]

Marine life

During this time, marine life (including ammonites and bivalves) flourished. Ichthyosaurs, although common, are reduced in diversity; while the top marine predators, the pliosaurs, grew to the size of killer whales and larger (e.g. Pliosaurus, Liopleurodon). Plesiosaurs became common at this time, and metriorhynchid crocodilians first appeared.

Terrestrial life

Many of the major groups of dinosaurs emerged during the Middle Jurassic, (including cetiosaurs, brachiosaurs, megalosaurs and primitive ornithopods).[3]

Descendants of the therapsids, the cynodonts were still flourishing along with the dinosaurs. These included the tritylodonts and mammals. Mammals remained quite small, but were diverse and numerous in faunas from around the world.[5][6] Tritylodonts were larger, and also had an almost global distribution.[7] The first crown group mammals appeared in the Middle Jurassic. A group of cynodonts, the trithelodonts, were becoming rare and eventually became extinct at the end of this epoch.

Flora

Conifers were dominant in the Middle Jurassic. Other plants, such as ginkgoes, cycads, and ferns were also common.

References

  1. ^ http://www.stratigraphy.org/index.php/ics-chart-timescale
  2. ^ British Geological Survey. 2011. Stratigraphic framework for the Middle Jurassic strata of Great Britain and the adjoining continental shelf: research report RR/11/06. British Geological Survey, Keyworth, Nottingham.
  3. ^ a b Benson RBJ, Campione NE, Carrano MT, Mannion PD, Sullivan C, Upchurch P, and Evans DC. 2014. Rates of dinosaur body mass evolution indicate 170 million years of sustained ecological innovation on the avian stem lineage. PLoS Biology 12, no. 5: e1001853.
  4. ^ Close RA, Friedman M, Lloyd GT, and Benson RB. 2015. Evidence for a mid-Jurassic adaptive radiation in mammals. Current Biology, 25(16), 2137-2142.
  5. ^ Kielan-Jaworowska, Z., Cifelli, R.L., and Luo, Z.-X. 2004. Mammals from the age of dinosaurs: origins evolution and structure. 630 pp. Columbia University Press, New York.
  6. ^ Panciroli, E. 2017. The First Mammals Palaeontology Online.
  7. ^ Kemp, T 2005. The Origin and Evolution of Mammals. Oxford University Press.
Archaeodontosaurus

Archaeodontosaurus ("ancient-toothed lizard") is a genus of sauropod dinosaur from the Middle Jurassic. Its fossils were found in the Isalo III Formation of Madagascar. The type species, Archaeodontosaurus descouensi, was described in September 2005. The specific name honours the collector, Didier Descouens. It is a probable sauropod, with prosauropod-like teeth.

Cladotheria

Cladotheria is a group (legion) of mammals that includes the ancestor of Dryolestoidea, Peramuridae and Zatheria (living therians plus all of its ancestors).

Coelurosauria

Coelurosauria (; from Greek, meaning "hollow tailed lizards") is the clade containing all theropod dinosaurs more closely related to birds than to carnosaurs.

Coelurosauria is a subgroup of theropod dinosaurs that includes compsognathids, tyrannosaurs, ornithomimosaurs, and maniraptorans; Maniraptora includes birds, the only dinosaur group alive today.Most feathered dinosaurs discovered so far have been coelurosaurs. Philip J. Currie considers it probable that all coelurosaurs were feathered. In the past, Coelurosauria was used to refer to all small theropods, but this classification has since been abolished.

Cruxicheiros

Cruxicheiros (meaning "cross hand") is a genus of tetanuran theropod dinosaur which lived in the Middle Jurassic of England. The type species is C. newmanorum, described by Roger Benson and Jonathan Radley in 2010.

Datousaurus

Datousaurus, meaning "Big-head Lizard" (from the Chinese da tou "Big Head" and Greek sauros/σαυρος "lizard") was a dinosaur from the Middle Jurassic. It was a sauropod collected from the Lower Shaximiao Formation in Dashanpu, Zigong Sichuan province, China. It shared the local Middle Jurassic landscape with other sauropods Shunosaurus, Omeisaurus and Protognathosaurus, the ornithopod Xiaosaurus and the early stegosaur Huayangosaurus as well as the carnivorous Gasosaurus.

Dryosauridae

Dryosaurids were primitive iguanodonts. They are known from Middle Jurassic to Early Cretaceous rocks of Africa, Europe, and North America.

Entradasuchus

Entradasuchus (meaning "Entrada [Sandstone and Ranch] crocodile") is a genus of crocodyliform, an early member of the group including crocodilians. The only known specimen was found in rocks of the Middle Jurassic Entrada Sandstone of Entrada Ranch, Grand County, Utah. Middle Jurassic terrestrial tetrapods are very rare, and Entradasuchus was the first unequivocal North American Middle Jurassic nonmarine tetrapod known from body fossils when it was described (1995).

Fenghuangopterus

Fenghuangopterus is a genus of basal pterosaur that lived in northeastern China during the Middle Jurassic.

The type species Fenghuangopterus lii was in 2010 described and named by Lü Junchang et al. The generic name is derived from the Fenghuang Mountain and a Latinised Ancient Greek pteron, "wing". The specific name honours Li Xiumei, who donated the fossil. It is known from a single relatively complete, though badly crushed, fossil skeleton, holotype CYGB-0037, recovered from the Tiaojishan Formation of Liaoning Province, about 160 million years old. It is a member of the rhamphorhynchid subfamily Scaphognathinae, which had previously been known only from the Late Jurassic and includes the close relatives Scaphognathus, Sordes and Harpactognathus.

Iguanodontia

Iguanodontia (the iguanodonts) is a clade of herbivorous dinosaurs that lived from the Middle Jurassic to Late Cretaceous. Some members include Camptosaurus, Dryosaurus, Iguanodon, Tenontosaurus, and the hadrosaurids or "duck-billed dinosaurs". Iguanodontians were one of the first groups of dinosaurs to be found. They are among the best known of the dinosaurs, and were among the most diverse and widespread herbivorous dinosaur groups of the Cretaceous period.

Jianchangnathus

Jianchangnathus is an extinct genus of basal pterosaur from the Middle Jurassic Tiaojishan Formation of northeastern China.

Jianchangopterus

Jianchangopterus is a genus of scaphognathine rhamphorhynchid pterosaur from the Middle Jurassic of western Liaoning, China. Jianchangopterus is known from a nearly complete skeleton with skull preserved. It was collected from the Tiaojishan Formation. It was first named (after Jianchang County) by Lü Junchang and Bo Xue in 2011 and the type species is Jianchangopterus zhaoianus.

Jobaria

Jobaria was a genus of sauropod dinosaur that lived in the current-day Niger during the middle Jurassic Period, between 164–161 million years ago.

Junggarsuchus

Junggarsuchus is an extinct genus of sphenosuchian crocodylomorph from the Middle Jurassic of China. The type species is J. sloani.

Orientognathus

Orientognathus is a genus of rhamphorhynchid pterosaur from the Middle Jurassic of China. It is known from a single specimen which includes most of the skeleton and skull, and was first named and described in 2015 by Lü Junchang et al.. The taxon was found in the Tuchengzi Formation of China, which is slightly younger than the Tiaojishan Formation that most other Middle Jurassic pterosaurs from the region have been found in. The description study produced a phylogenetic analysis, which determined that Orientognathus was a basal member of Rhamphorhynchidae, possibly within Rhamphorhynchinae.

Plectreuridae

Plectreuridae or plectreurid spiders are a small spider family confined to the Southwestern United States, Mexico, and the Caribbean. Only two living genera are known—the nominate genus Plectreurys and Kibramoa. In the past, the family was more widespread, with the Jurassic genus Eoplectreurys known from China, the Eocene Palaeoplectreurys baltica from Baltic amber and the Miocene Plectreurys pittfieldi from Dominican amber.These ecribellate, haplogyne spiders build haphazard webs under rocks and dead cacti. Adult males can be found wandering at night. Relatively little is known of their biology. Unlike the sicariids, scytodids, and diguetids, to which they are most closely related, they have eight eyes. In appearance females of Plectreurys resemble those of the larger species of the cribellate Filistatidae. They differ in their eye arrangement and in having the femurs on the first pair of legs bowed.

Scincomorpha

Scincomorpha is an infraorder of lizards. They first appear in the fossil record about 170 million years ago, during the Jurassic period.

Theria

Theria (; Greek: θηρίον theríon, wild beast) is a subclass of mammals amongst the Theriiformes (the sister taxon to Yinotheria). Theria includes the eutherians (including the placental mammals) and the metatherians (including the marsupials).

Yandusaurus

Yandusaurus is a genus of herbivorous basal euornithopod dinosaur from the Bathonian age (middle Jurassic, approximately 169 to 163 Ma) of China.

Zatheria

Zatheria is a group (sublegion) of mammals that includes the common ancestor of Arguimuridae, Vincelestidae, Peramuridae and Tribosphenida (living therians plus all of its ancestors).

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