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206-144Ma

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Jurassic Period

Part of the Mesozoic era which were comprised of the Triassic, Jurassic, and Cretaceous periods.

The Jurassic was named by Alexandre Brogniart (1770 – 1847) was a French chemist, mineralogist, and zoologist, for the extensive marine limestone exposures of the Jura Mountains, in the region where Germany, France and Switzerland meet. This period is usually broken into Early, Middle, and Late subdivisions, also known as Lias, Dogger and Malm. The corresponding terms for the rocks are Lower, Middle, and Upper Jurassic.

Fauna Development

Marsupials and humans share the same genetic imprinting that evolved 150 MA according to research published in Nature Genetics by a team of international scientists including the University of Melbourne, Department of Zoology.

Dinosaurs during this time included muttaburrasaurus, quetsalcoatlus, ankylosaurus. The dinosaurs died out towards the end of this period.The first snakes and modern mammals appeared.

Genomic imprinting is a mechanism that regulates gene expression in the developing fetus and plays a major role in regulating its growth. We all carry two copies of every gene in our DNA, one inherited from our mother and one from our father. So for each gene we have a ‘back-up’. Normally, both copies of the gene are used for development, but in some special cases the gene from either our mother or father is switched off, so we only have one active copy. This phenomenon is known as genomic imprinting.

A key gene regulating fetal growth is the Insulin-like-growth-factor-2 or IGF2 which is an imprinted gene. “We inherit a single working copy of this gene from our fathers, while the copy we inherit from our mothers is switched off. The switch for this gene is controlled by another gene known as H19. The H19 gene is unusual gene that makes a microRNA and not a protein.”

Geology

The Jurassic, best known for its dinosaurs, is also known for an important period geologically. Plate tectonics, or the movement of large portions of the Earth's crust in large plates, began to break up the single continent, Pangaea. The supercontinent Pangaea broke up into North America, Eurasia and the southern supercontinent Gondwana; the Gulf of Mexico opened in the new rift between North America and Gondwana. The Jurassic North Atlantic Ocean was relatively narrow, while the South Atlantic did not open until the following Cretaceous Period, when Gondwana itself rifted apart. The Tethys Sea closed, and the Neotethys basin appeared. Climates were warm, with no evidence of glaciation. As in the Triassic, there was apparently no land near either pole, and no extensive ice caps existed.

The Jurassic geological record is good in western Europe, where extensive marine sequences indicate a time when much of the continent was submerged under shallow tropical seas; famous locales include the Jurassic Coast World Heritage Site and the renowned late Jurassic lagerstätten of Holzmaden and Solnhofen. In contrast, the North American Jurassic record is the poorest of the Mesozoic, with few outcrops at the surface. Though the epicontinental Sundance Sea left marine deposits in parts of the northern plains of the United States and Canada during the late Jurassic, most exposed sediments from this period are continental, such as the alluvial deposits of the Morrison Formation.

Tamu Massif, an undersea mega volcano in the Northwest Pacific was formed about 145 million years ago. It is currently the largest volcano yet discovered on Earth rivaling the size of Martian volcanoes such as Olympus Mons. The discovery of its nature as a single volcano was announced on 5 September 2013

Terrestrial Fauna

On land, large archosaurian reptiles remained dominant. The Jurassic was the golden age of the great sauropods—Apatosaurus, Diplodocus, and many others—who roamed the land late in the period; their mainstays were either the prairies of ferns, palm-like cycads and bennettitales, or the higher coniferous growth, according to their adaptations. They were preyed upon by large theropods (Ceratosaurs, Megalosaurs, and Allosaurs). All these belong to the 'lizard hipped' or saurischian branch of the dinosaurs.

During the Late Jurassic, the first birds evolved from small coelurosaur dinosaurs. Ornithischian dinosaurs were less predominant than saurischian dinosaurs, although some like stegosaurs and small ornithopods played important roles as small and medium-to-large (but not sauropod-sized) herbivores. In the air, pterosaurs were common; they ruled the skies, filling many ecological roles now taken by birds.

As the World moved from the Triassic to the Jurassic, the boundary period saw great changes, in particular, the mass extinction of many mammal-like reptiles. These extinctions most likely removed competition for food sources and allowed the rapid diversification of the dinosaurs into many different ecological niches. Of particular note is the continued evolution toward larger dinosaurs such as the Vulcanodon which reached lengths of 30 feet or more.

It was also in this period that the familiar "long-necked" brachiosaurs evolved. Their morphological development allowed them to reach higher into the trees for vegetation. Other herbivores, such as the Stegosaurus and Hypsilophodon also evolved. Some herbivorous dinosaurs developed special biological enhancements for grazing such as the Scelidosaurus which evolved a turtle-like 'beak' for the grazing of low plants. Primitive iguanodonts such as Camptosaurus also developed features specifically adapted for grazing.

A Jurassic-period dinosaur which evolved from earlier ceratosaurs is the the double-crested Dilophosaurus, one of the largest of the Jurassic carnivores, reaching lengths of around 20 feet.

The carnosaurs, which began evolving in the Triassic, were much larger predators, and included dinosaurs such as Allosaurus.

Other dinosaurs that existed in the Jurassic include:

  • Brachiosaurus - Late Jurassic Period and possibly the Early Cretaceous Period.One of the largest animals known to have walked the earth, it has become one of the most famous of all dinosaurs and is recognized worldwide.
  • Abrictosaurus - a genus of heterodontosaurid dinosaur from the Early Jurassic Period of what is now southern Africa. It was a small bipedal herbivore or omnivore, approximately 1.2 meters (4 feet) long, and weighing less than 45 kilograms (100 pounds).
  • Abrosaurus - a genus of macronarian sauropod dinosaur from the Middle Jurassic Period of what is now Asia, one of many dinosaurs found at the Dashanpu Quarry in the Sichuan Province of China. Like most sauropods, Abrosaurus was a quadrupedal herbivore but it was rather small for a sauropod, not much more than 30 feet (9 m) long. Its head was boxy and topped with a tall bony arch containing the nostrils.
  • Adeopapposaurus - a genus of prosauropod dinosaur from the Early Jurassic Cañón del Colorado Formation of San Juan, Argentina. It was similar to Massospondylus. Four partial skeletons with two partial skulls are known. The type specimen, PVSJ568, includes a skull and most of a skeleton to just past the hips. The form of the bones at the tips of the upper and lower jaws suggests it had keratinous beaks.
  • Pterodactyls existed in China about 160 Million Years Ago. They have been called "Darwinopterus" after the renowned naturalist Charles Darwin

Aquatic and marine

During the Jurassic, the 'highest' life forms living in the seas were fish and marine reptiles. The latter include ichthyosaurs, plesiosaurs and marine crocodiles, of the families Teleosauridae and Metriorhynchidae.

In the invertebrate world, several new groups appeared, such as:

  • planktonic foraminifera and calpionelids, which are of great stratigraphic relevance;
  • rudists, a reef-forming variety of bivalves;
  • belemnites; and
  • brachiopods of the terebratulid and rinchonelid groups.

Ammonites (shelled cephalopods) are particularly common and diverse, forming 62 biozones.

Like gigantic, long-necked, sauropod dinosaurs roamed widely around the Earth 150 million years ago, scientists reported in the journal Current Biology. Their plant digestion was aided by methane-producing microbes which some have suggested may have produced enough methane to have an important effect on the Mesozoic climate.

Flora

The arid, continental conditions characteristic of the Triassic steadily eased during the Jurassic period, especially at higher latitudes; the warm, humid climate allowed lush jungles to cover much of the landscape. Conifers dominated the flora, as during the Triassic; they were the most diverse group and constituted the majority of large trees. Extant conifer families that flourished during the Jurassic included the Araucariaceae, Cephalotaxaceae, Pinaceae, Podocarpaceae, Taxaceae and Taxodiaceae. The extinct Mesozoic conifer family Cheirolepidiaceae dominated low latitude vegetation, as did the shrubby Bennettitales. Cycads were also common, as were ginkgos and tree ferns in the forest. Smaller ferns were probably the dominant undergrowth. Caytoniaceous seed ferns were another group of important plants during this time and are thought to have been shrub to small-tree sized. Ginkgo-like plants were particularly common in the mid- to high northern latitudes. In the Southern Hemisphere, podocarps were especially successful, while Ginkgos and Czekanowskiales were rare.

The ancestor of all flowering plants, including Amborella, evolved following a "genome doubling event" that occurred about 200 million years ago. Some duplicated genes were lost over time but others took on new functions, including contributions to the development of floral organs.

Sources

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Page last modified on December 22, 2013, at 01:58 PM