The name Jurassic comes from the Jura Mountains on the border of France and Switzerland (actually an extension of the Alps into eastern France) where rocks of this age were first studied by Alexander von Humbolt in 1795. In 1839 Leopold von Buch formally named the rocks described by von Humbolt as the Jurassic System, from whence the term has come into general use. The rock units Lias, Dogger, and Malm are often equated to the Early, Middle, and Late Jurassic Epochs, respectively; although these rock types are local English formations and should not be applied globally. There was a minor mass extinction toward the end of the Jurassic period during which most of the stegosaurid and enormous sauropod dinosaurs died out as did many genera of ammonoids, marine reptiles, and bivalves.
Tectonics and Paleoclimate
The Jurassic saw a continued split of Pangea. The super continent begins to rotate with the different components of the huge mass moving at different rates and then in different directions forming rift valleys. One of these opened the southern part of the North Atlantic Ocean and continued westward into the Gulf of Mexico. This was North America drifting westward, opening the Gulf of Mexico forming the central Atlantic. As Greenland-North America separate from Europe-Africa and slide over the Pacific Ocean floor, mountain-building events are triggered that created the North American Cordillera (the Rocky Mountains and the Sierra Nevada). A huge arc was built on western North America and the Nevadan orogeny begins. Cimmeria begins its collision with Laurasia to form the Cimmerian orogeny.
In Gondwanaland, the initial narrow split between South America and Africa that began during the Triassic widened into a configuration resembling the present-day Red Sea. A new sea floor formed along the South Atlantic. This lengthened into a long, narrow seaway between South America and Africa. The Western side South America was subducted by an opposing oceanic plate. A great rift separates Antarctica from the southern ends of South America and Africa developing an arm that extends eastward from South Africa along what is presently the eastern side of India which in turn began drifting northward.. Volcanoes located along these rifts erupted and issued huge amounts of basaltic lavas. The separated segments of Gondwanaland move slowly northward, turning gently counter-clockwise.
During the Jurassic the extent of the oceans was far more widespread then they had been in the Triassic. The Jurassic sea level rose and flooded large portions of the continents. The spreading ocean crawled across Russia and into what is now the Arctic Sea before retreating at the end of the period. Meanwhile, much of central North America was flooded by a wide sea way that at its height extended into central Utah. As a result, the Jurassic climate was warm and moist with greenhouse conditions prevailing throughout most land masses.
Flora during the Jurassic Period was dominated by cycads, conifer trees, cycadeoids, and ginkgos. Shrubs including Dicksoniaceous tree ferns and Caytoniaceous seed ferns were relatively successful plants during this time as were osmundaceous, matoniaceous, and dipteridaceous ferns which were probably the dominant undergrowth. Late during the Jurassic (about 140 million years ago) the first primitive flowering plants (angiosperms) evolved.
The warm tropical seas saw an explosion of phytoplankton and invertebrates including sponges, corals, bryozoa, gastropods, bivalves, ammonoid, and belemnite cephalopods including the ammonites, with their coiled external shells and the belemnites, close relatives of modern squid but with heavy, calcified, bullet-shaped, partially internal shells. Freshwater bivalves (clams), snails, and branchiopod were also common. In the oceans modern sharks evolved, giant marine crocodiles cruised the waterways, boney fish, which were mostly heavy scaled holostean animals, made their appearance as did the first teleost fishes. New types of ichthyosaurs replaced their Triassic predecessors and were joined by long-necked plesiosauroids and short-necked pliosauroids.
In the air were various types of pterosaur which were mostly small to medium-sized endothermic animals with a covering of fur. The first birds made their appearance.
On land, numerous groups of herbivorous insects were present including Orthoptera, Hemoptera, Psylloidea (plant hoppers), Pentatomoidea (shield bugs), Cimicoidea (plant bugs), Thysanoptera (thrips), Coleoptera (beetles), and primitive Hymenoptera (sawflies). Pulmonate snails, millipedes, scorpions, spiders and mites were mostly likely present, although there are currently no known fossils.
Some basal tetrapodomorphs amphibians survived into to Jurassic and were joined by frogs, newts, lizard-like animals, and crocodiles. Dinosaurs evolved into the dominate life form including huge sauropods reaching many tons in weight (e.g., Brachiosaurus, Apatosaurus , Camarasaurus, Diplodocus), more modestly sized browsers (e.g., Scelidosauridae, Stegosauridae, and iguanodonts), small fleet-footed herbivores (e.g., scutellosaurs, hypsilophodontids) and carnivores ranging from small lightly built predators (e.g.. Coelophysids, compsognathids, ornitholestids) to large meat-eaters (e.g., Dilophosaurus, Ceratosaurus, Allosaurus). Some of the smaller carnivores developed feathers and took to the air including the well-known Archaeopteryx. A diverse assembly of mammals evolved (e.g., Morganucodontids, Haramiyids, Docodonts, multiberculates, symmetrodonts, pantotheres) dining on plants, carrion, and insects much like modern-day rodents and insectivores.
Meteorite Impacts on Earth
I included a list of meteorite impacts relevant to this time period as a point of reference since many of the explanations for mass extinctions throughout Earth’s history include meteorite impact(s) as a possible cause. The meteorite impact information below was obtained from the ‘Earth Impact Database’ maintained by the Planetary and Space Science Centre, University of New Brunswick, Fredericton, New Brunswick, Canada ( www.passc.net/EarthImpactDatabase).