Jurassic. Etymology[edit] The chronostratigraphic term "Jurassic" is directly linked to the Jura Mountains. Alexander von Humboldt recognized the mainly limestone dominated mountain range of the Jura Mountains as a separate formation that had not been included in the established stratigraphic system defined by Abraham Gottlob Werner, and he named it "Jurakalk" in 1795.[4][5][6][7] The name "Jura" is derived from the Celtic root "jor", which was Latinised into "juria", meaning forest (i.e., "Jura" is forest mountains).[5][6][8] Divisions[edit] Key events in the Jurassic An approximate timescale of key Jurassic events.
Vertical axis: millions of years ago. Various dinosaurs roamed forests of similarly large conifers during the Jurassic period. Paleogeography and tectonics[edit] The Jurassic was a time of calcite sea geochemistry in which low-magnesium calcite was the primary inorganic marine precipitate of calcium carbonate. Fauna[edit] Aquatic and marine[edit] Terrestrial[edit] Flora[edit] See also[edit]
Toarcian turnover. The term Toarcian turnover, alternatively the Toarcian extinction, the Pliensbachian-Toarcian extinction, or the Early Jurassic extinction, refers to the wave of extinctions that marked the end of the Pliensbachian stage and the start of the Toarcian stage of the Early Jurassic period, c. 183 million years ago. See also[edit] Anoxic event References[edit]
Middle Jurassic. Late Jurassic. Triassic–Jurassic extinction event. Millions of years ago Tr–J The blue graph shows the apparent percentage (not the absolute number) of marine animalgenera becoming extinct during any given time interval. It does not represent all marine species, just those that are readily fossilized. The labels of the "Big Five" extinction events are clickable hyperlinks; see Extinction event for more details.
(source and image info) Impact[edit] At least half of the species now known to have been living on Earth at that time went extinct. Statistical analysis of marine losses at this time suggests that the decrease in diversity was caused more by a decrease in speciation than by an increase in extinctions.[5] Ranges of families tetrapods through the Triassic and Early Jurassic. Current theories[edit] Several explanations for this event have been suggested, but all have unanswered challenges: References[edit] Literature[edit] Hodych, J. External links[edit] Bird. Modern birds are characterised by feathers, a beak with no teeth, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a lightweight but strong skeleton. Extant birds have wings; the most recent species without wings was the moa, which is generally considered to have become extinct in the 16th century.
Wings are evolved forelimbs, and most bird species can fly. Flightless birds include ratites, penguins, and diverse endemic island species. Some species of birds, particularly penguins and members of the Anatidae family, are adapted to swim. Many species are economically important, mostly as game or poultry. Evolution and classification Definition Aves and a sister group, the clade Crocodilia, contain the only living representatives of the reptile clade Archosauria. Gauthier[8] identified four conflicting ways of defining the term "Aves", which is a problem because the same biological name is being used four different ways. Dinosaurs and the origin of birds. Theropoda. Biology[edit] Diet[edit] Theropods exhibit a wide range of diets, from insectivores to herbivores and carnivores. Strict carnivory has always been considered the ancestral diet for theropods as a group, and a wider variety of diets was historically considered a characteristic exclusive to the avian theropods (birds).
However, discoveries in the late 20th and early 21st centuries showed that a variety of diets existed even in more basal lineages.[1] All early finds of theropod fossils showed them to be primarily carnivorous. The first confirmed non-carnivorous fossil theropods found were the therizinosaurs, originally known as segnosaurs. Skin, scales and feathers[edit] Mesozoic theropods were also very diverse in terms of skin texture and covering. As of 2012, the most divergent known protofeathered theropod is Sciurumimus. Size[edit] Size comparison of selected giant theropod dinosaurs Tyrannosaurus was the largest theropod and best-known to the general public for many decades. Pterosaur. Pterosaurs are often referred to in the popular media and by the general public as flying dinosaurs, but this is incorrect. The term "dinosaur" is restricted to just those reptiles descended from the last common ancestor of the groups Saurischia and Ornithischia (clade Dinosauria, which includes birds), and current scientific consensus is that this group excludes the pterosaurs, as well as the various groups of extinct marine reptiles, such as ichthyosaurs, plesiosaurs, and mosasaurs.[7] (Like the dinosaurs, and unlike these other reptiles, pterosaurs are more closely related to birds than to any living reptile.)
Pterosaurs are also incorrectly referred to as pterodactyls, particularly by journalists.[8] "Pterodactyl" refers specifically to members of the genus Pterodactylus,[9] and more broadly to members of the suborder Pterodactyloidea of the pterosaurs.[10][11] Description[edit] The anatomy of pterosaurs was highly modified from their reptilian ancestors by the demands of flight. Plesiosauria. Plesiosaurs were among the first fossil reptiles discovered.
In the beginning of the nineteenth century, scientists realised how distinctive their build was and they were named as a separate order in 1835. The first plesiosaurian genus, the eponymous Plesiosaurus, was named in 1821. Since then over a hundred valid species have been described. In the early twenty-first century, the number of discoveries has increased, leading to an improved understanding of their anatomy, relationships and way of life. Plesiosaurs had a flat, broad body and a short tail. History of discovery[edit] Early finds[edit] First published plesiosaur skeleton, 1719 In 1719, William Stukeley described a partial skeleton of a plesiosaur, which had been brought to his attention by the great-grandfather of Charles Darwin, Robert Darwin of Elston. As this illustration shows, Conybeare by 1824 had gained a basically correct understanding of plesiosaur anatomy Plesiosaurus is named[edit] American discoveries[edit] Ichthyosaur.
Ichthyosaurs (Greek for "fish lizard" - ιχθυς or ichthys meaning "fish" and σαυρος or sauros meaning "lizard") were large marine reptiles. Ichthyosaurs belong to the order known as Ichthyosauria or Ichthyopterygia ('fish flippers' - a designation introduced by Sir Richard Owen in 1840, although the term is now used more for the parent clade of the Ichthyosauria). Science became aware of the existence of ichthyosaurs, during the early nineteenth century when the first complete skeletons were found in England. In 1834, the order Ichthyosauria was named. Later that century, many excellently preserved ichthyosaur fossils were discovered in Germany, including soft tissue remains.
Ichthyosaur species varied from one to over sixteen metres in length. History of discoveries[edit] Early finds[edit] The demand by collectors lead to more intense commercial digging activities. The first complete skeletons[edit] The skull found by Joseph Anning in 1811[8] The torso found by Mary Anning in 1812[8]