Early Jurassic

The Early Jurassic epoch (in chronostratigraphy corresponding to the Lower Jurassic series) is the earliest of three epochs of the Jurassic period. The Early Jurassic starts immediately after the Triassic-Jurassic extinction event, 201.3 Ma (million years ago), and ends at the start of the Middle Jurassic 174.1 Ma.

Certain rocks of marine origin of this age in Europe are called "Lias" and that name was used for the period, as well, in 19th-century geology.[2] In southern Germany rocks of this age are called Black Jurassic.

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]
The Three Patriarchs in Zion Canyon
Massive cliffs in Zion Canyon consist of Lower Jurassic formations, including (from bottom to top): the Kayenta Formation and the massive Navajo Sandstone.

Origin of the name Lias

There are two possible origins for the name Lias: the first reason is it was taken by a geologist from an English quarryman's dialect pronunciation of the word "layers"; secondly, sloops from north Cornish ports such as Bude would sail across the Bristol Channel to the Vale of Glamorgan to load up with rock from coastal limestone quarries (lias limestone from South Wales was used throughout North Devon/North Cornwall as it contains calcium carbonate to fertilise the poor quality Devonian soils of the West Country); the Cornish would pronounce the layers of limestone as 'laiyers' or 'lias'.

Geology

There are extensive Liassic outcrops around the coast of the United Kingdom, in particular in Glamorgan, North Yorkshire and Dorset. The 'Jurassic Coast' of Dorset is often associated with the pioneering work of Mary Anning of Lyme Regis. The facies of the Lower Jurassic in this area are predominantly of clays, thin limestones and siltstones, deposited under fully marine conditions.

Blue lias cliffs at Lyme Regis
Lias formations at Lyme Regis, UK, known locally as Blue Lias.

Lias Group strata form imposing cliffs on the Vale of Glamorgan coast, in southern Wales. Stretching for around 14 miles (23 km) between Cardiff and Porthcawl, the remarkable layers of these cliffs, situated on the Bristol Channel are a rhythmic decimetre scale repetition of limestone and mudstone formed as a late Triassic desert was inundated by the sea.[3]

Stratigraphy

There has been some debate[4] over the actual base of the Hettangian stage, and so of the Jurassic system itself. Biostratigraphically, the first appearance of psiloceratid ammonites has been used; but this depends on relatively complete ammonite faunas being present, a problem that makes correlation between sections in different parts of the world difficult. If this biostratigraphical indicator is used, then technically the Lias Group—a lithostratigraphical division—spans the Jurassic / Triassic boundary.

Life

Ammonites

During this period, ammonoids, which had almost died out at the end-of-Triassic extinction, radiated out into a huge diversity of new forms with complex suture patterns (the ammonites proper). Ammonites evolved so rapidly, and their shells are so often preserved, that they serve as important zone fossils. There were several distinct waves of ammonite evolution in Europe alone.[5]

Marine reptiles

The Early Jurassic was an important time in the evolution of the marine reptiles. The Hettangian saw the already existing Rhaetian ichthyosaurs and plesiosaurs continuing to flourish, while at the same time a number of new types of these marine reptiles appeared, such as Ichthyosaurus and Temnodontosaurus among the ichthyosaurs, and Eurycleidus, Macroplata, and Rhomaleosaurus among the plesiosaurs (all Rhomaleosauridae, although as currently defined this group is probably paraphyletic). All these plesiosaurs had medium-sized necks and large heads. In the Toarcian, at the end of the Early Jurassic, the thalattosuchians (marine "crocodiles") appeared, as did new genera of ichthyosaurs (Stenopterygius, Eurhinosaurus, and the persistently primitive Suevoleviathan) and plesiosaurs (the elasmosaurs (long-necked) Microcleidus and Occitanosaurus, and the pliosaur Hauffiosaurus).

Terrestrial animals

Drzewica Formation Reconstruction
Example of Rare Early Jurassic (Pliensbachian) Ecosystem, the Drzewica Formation of Szydłowiec, Poland. This zone was characterised by a very damp ecosystem populated by Dinosaur Megafauna, more related in several aspects to Middle or Late Jurassic Dinosaurs

On land, a number of new types of dinosaurs—the heterodontosaurids, scelidosaurs, stegosaurs, and tetanurans—appeared, and joined those groups like the coelophysoids, prosauropods and the sauropods that had continued over from the Triassic. Accompanying them as small carnivores were the sphenosuchian and protosuchid crocodilians. In the air, new types of pterosaurs replaced those that had died out at the end of the Triassic. But in the undergrowth were various types of early mammals, as well as tritylodont mammal-like reptiles, lizard-like sphenodonts, and early lissamphibians.

See also

References

  1. ^ http://www.stratigraphy.org/index.php/ics-chart-timescale
  2. ^ Rudwick, M.J.S (1992): Scenes from Deep Time: Early Pictorial Representations of the Prehistoric World, University of Chicago Press, 280 pages. Except from Google Books
  3. ^ Howe, S., Owen, G. & Sharpe, T. 2005 Walking the Rocks Geologists' Association - South Wales Group
  4. ^ International Subcommission on Jurassic Stratigraphy. Newsletter 35/1, December 2008, Edited by Nicol Morton and Stephen Hesselbo Archived 2015-01-28 at the Wayback Machine
  5. ^ See e.g. Davies, 1920, pp. 173–75

Sources

  • Davies, A. M., An Introduction to Palaeontology, Thomas Murby & Co., London
  • House, M.R. (1993) Geology of The Dorset Coast, The Geologists' Association.
  • Simms, M.J., Chidlaw, N., Morton, N. and Page, K.N. (2004) British Lower Jurassic Stratigraphy, Geological Conservation Review Series, No. 30, Joint Nature Conservation Committee, Peterborough.

External links

Barapasaurus

Barapasaurus ( bə-RAH-pə-SAWR-əs) is a genus of basal sauropod dinosaur from Early Jurassic rocks of India. The only species is B. tagorei. Barapasaurus comes from the lower part of the Kota Formation, that dates back to the Sinemurian and Pliensbachian stages of the early Jurassic. It is therefore one of the earliest known sauropods. Barapasaurus is known from approximately 300 bones from at least six individuals, so that the skeleton is almost completely known except for the anterior cervical vertebrae and the skull. This makes Barapasaurus one of the most completely known sauropods from the early Jurassic.

Chuxiongosaurus

Chuxiongosaurus is a genus of basal sauropodomorph dinosaur which lived during the Early Jurassic Period. Fossils of this genus have been found in the Lower Lufeng Formation, Yunnan Province, southern China. Identified from the holotype CMY LT9401 a nearly complete skull (including a lower jaw) with some similarities to Thecodontosaurus, it was described as the "first basal sauropod dinosaur from the Early Jurassic of China," more basal than Anchisaurus. It was named by Lü Junchang, Yoshitsugu Kobayashi, Li Tianguang and Zhong Shimin in 2010, and the type species is Chuxiongosaurus lufengensis.

Coelophysidae

Coelophysidae is a family of primitive carnivorous theropod dinosaurs. Most species were relatively small in size. The family flourished in the Late Triassic and Early Jurassic periods, and has been found on numerous continents. Many members of Coelophysidae are characterized by long, slender skulls and light skeletons built for speed. One member, Coelophysis, displays the earliest known furcula in a dinosaur.Under cladistic analysis, Coelophysidae was first defined by Paul Sereno in 1998 as the most recent common ancestor of Coelophysis bauri and Procompsognathus triassicus, and all of that common ancestor's descendants. However, Tykoski (2005) has advocated for the definition to change to include the additional taxa of "Syntarsus" kayentakatae and Segisaurus halli. Coelophysidae is part of the superfamily Coelophysoidea, which in turn is a subset of the larger Neotheropoda clade. As part of Coelophysoidea, Coelophysidae is often placed as sister to the Dilophosauridae family, however, the monophyly of this clade has often been disputed. The older term "Podokesauridae", named 14 years prior to Coelophysidae (which would normally grant it priority), is now usually ignored, since its type specimen was destroyed in a fire and can no longer be compared to new finds.

Coelophysoidea

Coelophysoidea were common dinosaurs of the Late Triassic and Early Jurassic periods. They were widespread geographically, probably living on all continents. Coelophysoids were all slender, carnivorous forms with a superficial similarity to the coelurosaurs, with which they were formerly classified, and some species had delicate cranial crests. Sizes range from about 1 to 6 m in length. It is unknown what kind of external covering coelophysoids had, and various artists have portrayed them as either scaly or feathered. Some species may have lived in packs, as inferred from sites where numerous individuals have been found together.

Examples of coelophysoids include Coelophysis, Procompsognathus and Liliensternus. Most dinosaurs formerly referred to as being in the dubious taxon "Podokesauridae" are now classified as coelophysoids.

Cryolophosaurus

Cryolophosaurus ( or ; "CRY-oh-loaf-oh-SAWR-us") is a genus of large theropods known from only a single species Cryolophosaurus ellioti, known from the early Jurassic period of Antarctica. It was about 6.5 metres (21.3 ft) long and 465 kilograms (1,025 lb) in weight, making it one of the largest theropods of its time. Individuals of this species may have grown even larger, because the only known specimen probably represents a sub-adult. Cryolophosaurus is known from a skull, a femur and other material, the skull and femur of which have caused its classification to vary greatly. The femur possesses many primitive characteristics that have classified Cryolophosaurus as a dilophosaurid or a neotheropod outside of Dilophosauridae and Averostra, where as the skull has many advanced features, leading the genus to be considered a tetanuran, an abelisaurid, a ceratosaur and even an allosaurid. Since its original description, the consensus is that Cryolophosaurus is either a primitive member of the Tetanurae or a close relative of that group.

Cryolophosaurus possessed a distinctive "pompadour" crest that spanned the head from side to side. Based on evidence from related species and studies of bone texture, it is thought that this bizarre crest was used for intra-species recognition. The brain of Cryolophosaurus was also more primitive than those of other theropods.

Cryolophosaurus was first excavated from Antarctica's Early Jurassic, Sinemurian to Pliensbachian aged Hanson Formation, formerly the upper Falla Formation, by paleontologist Dr. William Hammer in 1991. It was the first carnivorous dinosaur to be discovered in Antarctica and the first non-avian dinosaur from the continent to be officially named. The sediments in which its fossils were found have been dated at ~194 to 188 million years ago, representing the Early Jurassic Period.

Dilophosauridae

Dilophosauridae is a family of medium to large sized theropod dinosaurs. The name Dilophosauridae is derived from Greek, with “di” meaning “two,” “lophos” meaning “crest,” “sauros” meaning “lizard,” and “idae” meaning “family”. While the name suggests that all dilophosaurids have two crests, this is not applicable to all dilophosaurids. The Dilophosauridae is anchored by the genus Dilophosaurus, and therefore the name comes from the distinctive two crests of the genus.

Fabrosaurus

Fabrosaurus ( FAB-ro-SAWR-əs; meaning "Fabre's lizard" in honor of Jean Fabre, a French geologist and a colleague of Ginsburg on the expedition that collected the fossil in Basutoland, Southern Africa ; Greek sauros "lizard")) was a genus of herbivorous dinosaur which lived during the Early Jurassic (Hettangian to Sinemurian stages 199 - 189 mya).

Glacialisaurus

Glacialisaurus is a genus of massospondylid sauropodomorph dinosaur. It lived during the Early Jurassic period in what is now central Transantarctic Mountains of Antarctica. It is known from the holotype FMNH PR1823, a partial hind limb (foot) and from the referred material FMNH PR1822, a left femur.

Gymnophiona

Gymnophiona is the group of amphibians that includes the legless caecilians and all amphibians more closely related to them than to frogs or salamanders (the "stem-caecilians"). The name derives from the Greek words γυμνος (gymnos, naked) and οφις (ophis, snake), as the caecilians were originally thought to be related to snakes. The body is cylindrical dark brown or bluish black in colour. The skin is slimy and bears grooves or ringlike markings; there are minute dermal scales.

Gyposaurus

Gyposaurus (meaning "vulture lizard", referring to the outdated hypothesis that prosauropods were carnivores) is a genus of basal sauropodomorph dinosaur from the early Jurassic of South Africa. It is usually considered to represent juveniles of other prosauropods, but "G." sinensis is regarded as a possibly valid species in recent reviews of the prosauropods (Galton and Upchurch, 2004).

Ichthyosaurus

Ichthyosaurus (derived from Greek ιχθυς/ichthys meaning 'fish' and σαυρος/sauros meaning 'lizard') is a genus of ichthyosaurs from the late Triassic and early Jurassic (Rhaetian - Pliensbachian) of Europe (Belgium, England, Germany, Switzerland) and Asia (Indonesia). It is among the best known ichthyosaur genera, as it is the type genus of the order Ichthyosauria.

Iguanomorpha

Iguania is an infraorder of squamate reptiles that includes iguanas, chameleons, agamids, and New World lizards like anoles and phrynosomatids. Using morphological features as a guide to evolutionary relationships, the Iguania are believed to form the sister group to the remainder of the Squamata. However, molecular information has placed Iguania well within the Squamata as sister taxa to the Anguimorpha and closely related to snakes. Iguanians are largely arboreal and usually have primitive fleshy, non-prehensile tongues, although the tongue is highly modified in chameleons. The group has a fossil record that extends back to the Early Jurassic (the oldest known member is Bharatagama, which lived about 190 million years ago in what is now India).

Jingshanosaurus

Jingshanosaurus (meaning "Jingshan lizard") is a genus of sauropodomorph dinosaurs from the early Jurassic period.

Mesoeucrocodylia

Mesoeucrocodylia is the clade that includes Eusuchia and crocodyliforms formerly placed in the paraphyletic group Mesosuchia. The group appeared during the Early Jurassic, and continues to the present day.

Neosuchia

Neosuchia is a clade within Mesoeucrocodylia that includes all modern extant crocodilians and their closest fossil relatives. It is defined as the most inclusive clade containing all crocodylomorphs more closely related to Crocodylus niloticus (the Nile Crocodile) than to Notosuchus terrestris. Neosuchia is very diverse and may be polyphyletic, as the clade has undergone many revisions since it was first named in 1988. Neosuchians first appear in the Early Jurassic with the earliest known goniopholid Calsoyasuchus, which lived during the Sinemurian and Pliensbachian stages.

Pulanesaura

Pulanesaura is an extinct genus of basal sauropod known from the Early Jurassic (late Hettangian to Sinemurian) Upper Elliot Formation of the Free State, South Africa. It contains a single species, Pulanesaura eocollum, known from partial remains of at least two subadult to adult individuals.

Squamata

Squamata is the largest order of reptiles, comprising lizards, snakes and amphisbaenians (worm lizards), which are collectively known as squamates or scaled reptiles. With over 10,000 species, it is also the second-largest order of extant (living) vertebrates, after the perciform fish, and roughly equal in number to the Saurischia (one of the two major groups of dinosaurs). Members of the order are distinguished by their skins, which bear horny scales or shields. They also possess movable quadrate bones, making it possible to move the upper jaw relative to the neurocranium. This is particularly visible in snakes, which are able to open their mouths very wide to accommodate comparatively large prey. Squamata is the most variably sized order of reptiles, ranging from the 16 mm (0.63 in) dwarf gecko (Sphaerodactylus ariasae) to the 5.21 m (17.1 ft) green anaconda (Eunectes murinus) and the now-extinct mosasaurs, which reached lengths of over 14 m (46 ft).

Among other reptiles, squamates are most closely related to the tuatara, which superficially resembles lizards.

Tazoudasaurus

Tazoudasaurus is a genus of vulcanodontid sauropod dinosaurs hailing from the Early Jurassic Toundoute Group located in the High Atlas Mountains of Morocco in North Africa. The remains, consisting of a partial adult skeleton and associated partial juvenile skeleton found in continental detrital sediments of the Toarcian aged Toundoute Continental Series, were described by Ronan Allain et al. in early 2004. The generic name derives from one of the localities, Tazouda, while the specific descriptor is a latinization of the Arabic term for "slender" due to the animal's small size for a sauropod. Its fossil was found alongside that of Berberosaurus.

Tazoudasaurus, a small sauropod at 9 meters (30 feet) long, is characterized by rather primitive features such as the prosauropod-like mandible with spatulate and denticle-bearing teeth, lack of a U-shaped mandibular symphysis as other more derived sauropods. Teeth wear in V-shaped marks indicates tooth occlusion, suggesting that vulcanodontids processed food orally when feeding. The neck is flexible with elongate vertebrae that lack true pleurocoels while dorsal and caudal vertebrae series tend to be more rigid. T. naimi bears the most complete fossil skeleton for Early Jurassic sauropod remains found to date due to the scarcity of exposed strata of that age. This sauropod is most closely related to Vulcanodon, differing only in caudal vertebrae features while it also possesses characters that place it outside Eusauropoda.

Vulcanodontidae

The Early Jurassic sauropod dinosaurs Zizhongosaurus, Barapasaurus, Tazoudasaurus, and Vulcanodon may form a natural group of basal sauropods called the Vulcanodontidae. Basal vulcanodonts include some of the earliest known examples of sauropods. The family-level name Vulcanodontidae was erected by M.R. Cooper in 1984. In 1995 Hunt et al. published the opinion that the family is synonymous with the Barapasauridae. One of the key morphological features specific to the family is an unusually narrow sacrum.

Cenozoic era
(present–66.0 Mya)
Mesozoic era
(66.0–251.902 Mya)
Paleozoic era
(251.902–541.0 Mya)
Proterozoic eon
(541.0 Mya–2.5 Gya)
Archean eon (2.5–4 Gya)
Hadean eon (4–4.6 Gya)

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