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Jurassic Period: 199.6-145.5 Million Years Ago

The Jurassic period extends from 199.6 to 145.5 million years ago. The Jurassic period was named for the Jura Mountains by the French chemist Alexandre Brongniart (1770-1847). The Jura Mountain range lies in an area between France, Germany and Switzerland and contains limestone exposures of Jurassic age. Although set back by the Triassic crises, life recovers and diversifies.

Primary Producers & Reefs

Extinction at the end of the Triassic disrupted the adaptive radiation of dinofagellates and coccolithophores. Eighty percent of marine species were eliminated by this crisis. One genus representing coccolithophorids and two the dinoflagellates crossed over into the Jurassic period. During the early Jurassic primary production was dominated by green algal phytoplanktons, which grow well in anoxic conditions (Payne & Schootbrugge, 2007, p. 179). However, dinoflagellates and coccolithophorids not only recover they are joined by a new type of protist, the diatoms. Diatoms (phylum Heterokontophyta) make their first appearance during the Jurassic. Diatoms are unicellular or colonial eukaryotic phytoplankton. Diatoms are the most successful of the phytoplankton in today’s oceans in terms of biomass and net primary production. Diatoms are encased in a two-part, asymmetrical silica cell wall. The two halves of the silica case fit together like the parts of a petri dish. The diatom’s silica shell is called a frustule. With the appearnce of diatoms, the transition to the modern primary producers could now occur. Diatoms, dinoflagellates, and coccolithophores would assume their dominant role as the base of many modern marine ecosystems by Cretaceous times. Reefs were absent during the early Jurassic. Sponges, Tubiphytes, corals, and microbial mounds were the major contributors to reestablishing reefs. Toward the end of the Jurassic scleractinian corals and stromatoporoids would once again be the primary reef builders (Webb, 2001, p. 176).

Mesophytic flora continued to diversify during the Jurassic period with seed plants dominating communities. Cycads, ginkgos, bennettitaleans, and conifers underwent adaptive radiations. Modern conifer families including Pinaceae, Taxodiaceae, Cupressaceae, and Cephalotaxaceae make their first appearance (Willis & McElwain, 2002, p. 148). Gymnosperms were the dominant trees including a variety of conifers and ginkgos. Bennettitaleans dominated the role of small trees and bushes. Ferns continued to flourish as the dominant herbaceous plants (Dodsen, 1997, p. 388). Representatives of the order Ginkgoales date back to the Permian, but the genus Ginkgo makes its first appearance in the Jurassic.

Holzmaden Shale
The supercontinent Pangaea started to break up during the Triassic. As the continents rifted apart epicontinental seas formed supporting coral reefs and providing an environment in which reptiles could diversify and flourish. The Holzmaden shale, located near Stuttgart in Germany, is a conservation lagerstatten that provides a window into one of these Jurassic-aged epicontinental seas. The Holzmaden shale and its fossils represent a community living in a subtropical epicontinental marine basin.

Echinoderms (such as crinoids, echinoids, and ophiuroids) and mollusks (gastropods and bivalves) were the primary consumers. Bony fish and cephalopods (ammonites, squid, and belemnoids) preyed on these primary consumers. Ichthyosaurs, plesiosaurs, sharks, and crocodiles were the top predators. Small sauropod dinosaurs, horsetails, ginkgos, cycads, and conifers provide clues to the vegetation supported by nearby landmasses.

The Holzmaden lagerstatten is most famous for the important insights it gives paleontologists into the anatomy and life of ichthyosaurs. On some specimens a black organic film provides an outline of the body around the skeletal structure. The black outline revealed that the ichthyosaur Stenopterygius had a fleshy dorsal fin and upper lobe on the tail. Female ichthyosaurs fossilized with embryos in their bodies indicate they gave live birth at sea. Stomach contents reveal a diet of fish and cephalopods (Selden & Nudds, 2004, pp. 79-87).

Morrison Formation
The Morrison Formation of North America represents Jurassic-aged terrestrial environments. The age of the Morrison formation has been determined to be Late Jurassic (155 to 148 million years ago) independently using microfossil analysis and radiometric dating. The Morrison Formation of North America is known from twelve different states. Museums around the world display Morrison Formation fossils.

The Morrison Formation covers an area greater than 1.5 million square kilometers in the western United States. The Morrison Formation represents a variety of terrestrial environments. In the Southwest eolian sandstones mark the existence of past hot, arid deserts. Towards the north, sandstones and conglomerates mark the paths of ancient meandering rivers. Next to the ancient rivers mudstone deposits tell the story of sediments spilling out over the riverbanks into the floodplain. Thin limestone deposits mark the location of lakes and ponds. In Montana, Morrision coal deposits indicate a wet, swampy environment (Carpenter, 1997, p. 451).

For paleontologists hunting dinosaurs it is the river and lake deposits that have been the most productive. Bones of large dinosaurs and other Mesozoic animals deposited by flash floods form Concentration Lagerstatte in Colorado, Utah, and Wyoming, These deposits provide important insights into some Jurassic terrestrial ecosystems. The Morrison Formation was deposited in a semi-arid basin with meandering rivers and lakes following the retreat of the Sundance Sea. Evidence suggests this environment was influenced by cycles of drought and flood. During times of drought dinosaur herds concentrated around disappearing water sources. Drought created mass death assemblages. Carcasses of the dead decomposed and dried. Periodic floods deposited the disarticulated bones in river channels. Allosaurus, Diplodocus, Apatosaurus, Camarasaurus, and stegosaurus are among the most famous Morrison Formation dinosaurs. The Morrison biota also includes: lizards, crocodiles, turtles, pterosaurs, many primitive mammals, fish, invertebrates, bryophytes, ferns, cycads, ginkgos, and conifers (Selden & Nudds, 2004, pp. 88-98).

The Morrison Formation became famous due to an intense competition between two American palaeontologists, which started in 1877. Professor Othniel Charles Marsh (1831-1899) of Yale’s Peabody Museum and Edward Drinker Cope (1840-1897) were fierce rivals that strove to scientifically outdo one another by discovering and describing new fossil organisms. The feud between these two noted paleontologists is known as the “bone wars”. The bone wars continued until Cope’s death in 1897. Marsh had described 75 new dinosaur species of which 19 are valid today. Cope had described 55 new species of dinosaurs of which 9 are valid today (Selden & Nudds, 2004, p. 90).

The bone wars had a tremendous impact on paleontology. Spectacular discoveries of complete dinosaur skeletons improved our understanding of dinosaurs and the evolution of life. The discoveries made in the Morrison Formation helped to fuel explorations worldwide (Breithaupt, 1997, pp. 347-350).

Solnhofen Limestone

The Solnhofen Limestone of Bavaria in Southern Germany is an important Conservation Lagerstatten that preserves both terrestrial and marine life of the Late Jurassic (150 MA). The deposit consists of finely laminated, micritic limestone known as lithographic limestone. The fine grained limestone was excavated to produce limestone slabs that could be etched with acid to make lithographic plates used to print illustrations. The fine grained micritic limestone helped to preserve the intricate details of feathers, insect wings, and squid tentacles as impressions. Examples of organic material preservation include cephalopod ink sacs and feathers. Soft tissues, such as the muscles of fish and cephalopods are sometimes replaced by francolite (calcium phosphate).

Solnhofen Limestone represents a subtropical, saline lagoon community with a semi-arid monsoonal climate. The bottom and lower layers of the lagoon were inhospitable to life. Over 600 species make up the Solnhofen Limestone biota. The majority of fossils represent organisms swept into the lagoon during storms. These organisms lived in adjacent land and reef communities as well as the open sea.

Archaeopteryx specimens, representing the earliest known bird, are the most famous Solnhofen fossil. Compsognathus is the only dinosaur found in this deposit. Pterosaurs are represented by Rhamphorhynchus, Scaphognathus, and Pterodactylus. Crocodiles, turtles, lizards, and the teeth of ichthyosaurs and plesiosaurs are known. Ray-finned fish, lobe-finned fish, and cartilaginous fish have been described. Shrimps, lobsters, crabs, and horseshoe crabs represent crustaceans. Perhaps the most interesting fossils are those of Mesolimulus, horseshoe crabs preserved at the end of their spiraling death trails. It is believed they quickly died after being swept into the toxic lagoon bottom. Insects are represented by mayflies, dragonflies, cockroaches, termites, water skaters, locusts, crickets, water scorpions, cicadas, lacewings, beetles, caddis flies, true flies, and wasps. Many marine invertebrate groups are represented such as sponges, cnidarians (jellyfish and corals), annelids, bryozoans, brachiopods, mollusks (gastropods, bivalves, and cephalopods), and echinoderms (crinoids, starfish, brittle stars, sea urchins, and sea cucumbers). Plant life preserved in Solnhofen Limestone includes seed ferns, bennettitales, ginkgos, and conifers (Selden & Nudds, 2004, pp. 99-108).


A minor extinction event near the end of the Jurassic period affected both marine and terrestrial life. The primary victims included marine invertebrates and dinosaurs. Among marine organisms bivalves and ammonoids suffered the most. Many marine crocodiles and ichthyosaurs would not survive into the Cretacous. Among terrestrial organisms the stegosaurs and most sauropod groups went extinct. It was once thought that drops in sea levels contributed to the Jurassic loses, but current evidences suggests this is not the case (Stanley, 1987, pp. 121-122).


  • Benton, M.J. (2005) Vertebrate Palaeontology [3rd Edition]. Blackwell Publishing: Main, USA.

  • Breithaupt, B.H. (1997). II. First Golden Period in the USA. In Currie, P.J. & Padian, K. [Eds]. Encyclopedia of Dinosaurs (pp. 347& 350). New York: Academic Press.

  • Buttler, C., Cope, C.W., & Owens, R.M. (2009). Jurassic Invertebrates. In Guerrero, A.G., Frances, P., & Stradins, I. [Eds]. Prehistoric Life: The Definitive Visual History of Life on Earth (pp. 234-243). New York: Dorling Kindersley.

  • Carpenter K. (1997). Morrison Formation. In Currie, P.J. & Padian, K. [Eds]. Encyclopedia of Dinosaurs (p. 451). New York: Academic Press.

  • Carpenter, F.M., & Burnham, L. (1985). The Geologic Record of Insects. Annual Review of Earth and Planetary Sciences 13: 297-314.

  • Dixon D., Cox, B., Savage, R.J.G., & Gardiner, B. (1988). The Macmillan Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals: A Visual Who’s Who of Prehistoric Life. New York: Macmillan Publishing Company.

  • Dodson, P. (1997). Jurassic Period. In Currie, P.J. & Padian, K. [Eds]. Encyclopedia of Dinosaurs (pp. 387 & 388). New York: Academic Press.

  • Falkowski, P.G. Knoll, A.H. (2007). Evolution of Primary Producers in the Sea. China: Elsevier Academic Press.

  • Grimaldi, D. & Engel, M.S., (2005). Evolution of the Insects. New York: Cambridge University Press.

  • Kemp, T.S. (2005). The Origin and Evolution of Mammals. New York: Oxford University Press.

  • Lessem, D. & Glut, D. (1993). The Dinosaur Society's Dinosaur Encyclopedia. New York: Random House.

  • Lu, J., Unwin, D.M., Jin, X., Liu, Y., Ji, Q. (2009) Evidence for modular evolution in a long-tailed pterosaur with a pterodactyloid skull. Proceedings of The Royal Society Biological Sciences, pp 1-7. (doi: 10.1098/rspb.2009.1603).

  • McIntosh, J.S. (1990). Sauropoda. In Weishampel, D.B., Dodson, P., & Osmolska, H. [Eds]. The Dinosauria (pp. 345-401). Berkeley: University of California Press.

  • Osmolska, H. (1997). Ornithomimosauria. In Currie, P.J. & Padian, K. [Eds]. Encyclopedia of Dinosaurs (pp. 499-503). New York: Academic Press.

  • Padian, K. (1997). Dinosauria: Definition. In Currie, P.J. & Padian, K. [Eds]. Encyclopedia of Dinosaurs (pp. 175-179). New York: Academic Press.

  • Payne, J.L. & Van De Schootbrugge, B. (2007). Life in Triassic Oceans: Links Between Planktonic and Benthic Recovery and Radiation. . In Falkowski, P.G. Knoll, A.H. [Eds] Evolution of Primary Producers in the Sea. (pp. 165-189). China: Elsevier Academic Press.

  • Prothero, D.R. (1998). Bringing Fossils to Life: An Introduction to Paleobiology. New York: McGraw-Hill.

  • Prothero, D.R. (2004). Bringing Fossils to Life: An Introduction to Paleobiology [2nd edition]. New York: McGraw-Hill.

  • Rose, K.D. (2006). The Beginning of the Age of Mammals. Baltimore: The Johns Hopkins University Press.

  • Selden P. & Nudds, J. (2004). Evolution of Fossil Ecosystems. Chicago: The University of Chicago Press.

  • Stanley, S.M., (1987). Extinction. New York: Scientific American Books.

  • USGS Publication: Major Division of Geologic Time see:

  • Waggoner, B. (1995). Theropod Dinosaurs:

  • Webb, G.E. (2001). Biologically Induced Carbonate Precipitation in Reefs through Time. In Stanley, G.D. Jr. [Ed] The History and Sedimentology of Ancient Reef Systems (159-203). New York: Kluwer Academic/Plenum Publishers.

  • Willis, K.J. & McElwain, J.C. (2002). The Evolution of Plants. New York: Oxford Univeristy Press.

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