The Jurassic Period began as a large extinction took place at the end of the Triassic period, approximately 208-200 ma, and later extended to 144 million years ago, roughly 64 ma to 56 ma total. At the beginning, the continent, Pangaea, began to separate significantly for the first time. This may have given cause to the mass extinction, as the separation would have triggered a great deal of volcanic activity. The resulting environment gave way to what may be considered the golden age of the ruling dinosaurs. The Jurassic period is divided into the following subdivisions:

A Shifting Climate and Developing Oceans

At the start of the period, the breakup of the supercontinent Pangaea continued and accelerated. Laurasia, the northern half, broke up into North America and Eurasia. Gondwana, the southern half, began to break up by the mid-Jurassic. The eastern portion—Antarctica, Madagascar, India, and Australia—split from the western half, Africa and South America. New oceans flooded the spaces in between. Mountains rose on the seafloor, pushing sea levels higher and onto the continents.

All this water gave the previously hot and dry climate a humid and drippy subtropical feel. Dry deserts slowly took on a greener hue. Palm tree-like cycads were abundant, as were conifers such as araucaria and pines. Ginkgoes carpeted the mid- to high northern latitudes, and podocarps, a type of conifer, were particularly successful south of the Equator. Tree ferns were also present.

The oceans, especially the newly formed shallow interior seas, teemed with diverse and abundant life. At the top of the food chain were the long-necked and paddle-finned plesiosaurs, giant marine crocodiles, sharks, and rays. Fishlike ichthyosaurs, squidlike cephalopods, and coil-shelled ammonites were abundant. Coral reefs grew in the warm waters, and sponges, snails, and mollusks flourished. Microscopic, free-floating plankton proliferated and may have turned parts of the ocean red.

Fauna

Dinosaurs continued as the dominant species and evolved to be gigantic. Many titanic sauropods became common including the Seismosaurus, and the Brachiosaurus. These were pursued by large predators like the Ceratosaurus, and the well-known Allosaurus. These large dinosaurs may have influenced the evolution of the first armored dinosaurs like the Stegosaurus.

In the air, pterosaurs were common; they ruled the skies, filling many ecological roles now taken by birds. Within the undergrowth were various types of early mammals, as well as tritylodonts, lizard-like sphenodonts, and early lissamphibians.

Dinosaur Groups

Saurischia (“lizard-hipped” dinosaurs) contains two main groups:

  • Sauropodomorpha includes both the “prosauropods” and the Sauropoda. Prosauropods were probably a paraphyletic (artificial) group of largely herbivorous, dominantly bipedal dinosaurs such as Plateosaurus. The Sauropoda were long-necked, long-tailed, enormous herbivorous dinosaurs such as Brachiosaurus, Diplodocus, and Apatosaurus.

  • Theropoda consists of the carnivorous dinosaurs. The Theropoda includes some extinct dinosaurs such as Tyrannosaurus rex and Dilophosaurus. Birds descended from Theropoda.

Ornithischia (“bird-hipped” dinosaurs) contains three primary groups:

  • Thyreophora includes the various armored dinosaurs such as Stegosaurus and Ankylosaurus.
  • Marginocephalia consists mainly of the pachycephalosaurs (bone heads) and the ceratopsians (horned dinosaurs) such as Triceratops.
  • Ornithopoda includes not only small bipedal plant eaters like Hypsilophodon but also the often large hadrosaurs (duck-billed dinosaurs) like Maiasaura and Edmontosaurus.

Marine Life

During the Jurassic period, the primary vertebrates living in the sea were fish and marine reptiles. The latter include ichthyosaurs, who were at the peak of their diversity, plesiosaurs, pliosaurs, and marine crocodiles of the families Teleosauridae and Metriorhynchidae. Numerous turtles could be found in lakes and rivers.

In the invertebrate world, several new groups appeared, including rudists (a reef-forming variety of bivalves) and belemnites. Calcareous sabellids (Glomerula) appeared in the Early Jurassic. The Jurassic also had diverse encrusting and boring (sclerobiont) communities, and it saw a significant rise in the bioerosion of carbonate shells and hardgrounds. Especially common is the ichnogenus (trace fossil) Gastrochaenolites.

During the Jurassic period, about four or five of the twelve clades of planktonic organisms that exist in the fossil record either experienced a massive evolutionary radiation or appeared for the first time.

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. Gymnosperms were relatively diverse during the Jurassic period. The Conifers in particular 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 Dicksoniaceous 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 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.

End

Near the end of the Jurassic period several species died out giving rise to the Cretaceous period. This transition was not as violent as the mass extinction at the beginning of the Jurassic period nor as devastation as what would come near the end of the Cretaceous. However, it led to another era and bid farewell to one of the most dynamic epochs of earth's history.

Walking With Dinosaurs Episode 2 - A Time of the Titans :biggus-piggus:

Walking With Dinosaurs Episode 3 - Cruel Sea :fishe:

Jurassic Era (Part two) : the age of Dinosaurs :shocked-dino:

Jurassic Era (Part one) : the ocean :croc-pog:

How Did Dinosaurs Get So Huge? PBS eons
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  • shimmer [undecided]
    ·
    2 years ago

    Hey congrats. Knowing what you want and don't want and making steps is huge. I think you'll be okay.