Jurassic Period

Events marking the beginning and end of the Jurassic period

• The Jurassic period was from about 208 million years ago until 145 million years ago
.
• These 63 million years were also known as the age of the dinosaurs. At the end of the period there was one of mass extinctions associated with the dinosaurs (Condie, 344).
• This dinosaur extinction was paralleled by a shift in dominate vegetation from the conifers and cycads of the Jurassic period to shorter, primitive flowering trees (346). It was this change in vegetation that may have led to the extinction of some of the species of dinosaurs.
• In the late Jurassic the two super continents Laurasia and Gondwana were separated by a broad seaway, the Tethyan Seaway (Fastovsky, 35).

Climate/ecological communities

• The overall climate of the period was warm and mild with less seasonality than is currently experienced (Fastovsky, 46).
• Partly due to the presence of the Western Interior Seaways; large bodies of water tend to stabilize temperatures (Fastovsky, 35).
No polar ice on northern parts of continents, creating higher sea levels (Fastovsky, 44).

Pangea was continuous land with warm conditions all the way to the poles. Fossils of subtropical ferns have been found as far north as what is now known as Greenland and as far south as Antarctica (Benton, 1990).

At the beginning of the era, there seems to have been a spread of marine waters and shallow seas "advanced across many continental regions." (Colbert, 1969)

Vegetation consisted of low ferns, horsetails, seed ferns, conifers, and cycads (Benton, 1990). Some say that the Jurassic period may as well have been called the age of the Cycads because they are the most common impression fossil found from this time period (Stewart, 1983). While most of the species went extinct at the end of the period, cycads still exist today and can be found in people gardens and a few in the wild.

Coevolution between insects and angiosperms may have been initiated this early (Stewart, 1983). [Coleoptera, Diptera, Hymentoptera, and Lepidoptera]

The ocean was still filled with jawed fish and was dominated by the large predators Ichthyosaurs and Plesiosaurs, reptiles that lived in the sea (Cooper, 1969). Ammonites were also abundant.

Dinosaurs were the dominant land animals. Mammals continued to be small and stay in the shadows of the larger dinosaurs (Colbert, 1969).

Continental drift

The continents were relatively stable during this time period. Pangea was continuing to break up, and by the end of the Late Jurassic the separation of Laurasia and Gonwana was complete (Fastovsky, 35). No polar ice creating lots of water to stabilize the temperature.



Pictures taken from http://vishnu.glg.nau.edu/rcb/Jur.jpg and http://vishnu.glg.nau.edu/rcb/150NAt.jpg

Adaptive radiations

• Most adaptive radiation that occurred was diversification of dinosaurs.
• After the end-Triassic extinction, there was an opportunistic evolution of the dinosaurs (Fastovsky, 104).
• The middle Jurassic should have been an important period in the evolution of dinosaurs but terrestrial sediments from that time are rare (Fastovsky, 35).

There were two large clades of dinosaurs: Ornithischia (pelvis similar that found in birds) and Saurischia. (Fastovsky)

• Ornitischia: very diverse clade, includes armored (Thyreophora; Stegosauria) and duckbilled dinosaurs (Ornithopoda; first show up in fossil record during early Jurassic).
• Saurishia: clad that contains the smallest of the dinosaurs and the super giants, the most agile predators and the slow plant-eaters, all who share more than 15 derived features. Includes the Sauropodomorphia (the huge sauropods ­ diverged from other dinosaurs during late Triassic (Upchurch, 1995)), Theropoda (the preditors; allosaurus. It was from this group that birds probably derived)

Dinosaurs ranged in size from Compsognathus, who weighed only about two pounds (about the size of a chicken), to the some of the largest land animal ever the sauropods including Apatosaurus (aka Brontosarus) which weighed in at 30 tons.

A few myths about dinosaurs:

Sauropods did not use their long necks as snorkels because the pressure of the water would be too great for the lungs to expand (Cowen, 1997).

The complexity of dinosaurs social structure and parental care are better compared to living mammals and birds that living reptiles (Cowen, 200).

• Rapid diversification of ferns, cycads, cycadeoids, conifers, and ginkophytes, with all groups reaching their maximum abundance during this period (Stewart, 1983).

Extinctions

The Jurassic Period did not experience that many mass extinctions being a fairly stable time period.

However, there were a few minor extinctions including a loss of approximately 84% of bivalve species (Hallam, 1997).

This decrease seems to have occurred towards the beginning of the period and then a rise to a level it remained constant at for the rest of the period (Hallam, 1977).

Corresponds with a rapid sea-level rise (Hallam, 1997).

Extinction of the glossopterids (Stewart, 1983)

Evolutionary Steps

The late Jurassic is at the time that birds were believed to have evolved.

They were not the only ones occupying the air; there was convergent evolution of flight by the birds and by the flying reptiles such as the pteredon.

The famous fossil of the bird is Archaeopteryx, found in West Germany and recently there has been a discovery of another bird fossil from the same time period in China indicating that the spread of different species of these primitive birds may be wider than previously imagined (Chatterjee, 1997).

Period where also see the first fossils of the chrysophyta (diatoms) (Stewart, 1983).

Fossil resources

Major sites around the world for finding Jurassic fossils

• Upper Jurassic Solenhofen Limestond. Bavaria, West Germany: finding site of Archaeopteryx, sponges, coral
• Morrison Formation. Rocky Mountains, USA: : over 100 dinosaur quarries to date, rich in plant fossils.
• Berlin ­ Ichthyosaur State Park, Nevada: major finds include 25 ichthysaur fossils, some of the largest and most complete at least in North America
(http://www.ucmp.berkeley.edu/mesozoic/jurassic/jurassicloc.html)

Glossary of terms

Ichthyosaurs

members of the order Ichthyopterygia. A marine reptile with a dolphin-like body shape and large eyes that was one of the major predators of the sea at this time. They swam by beating their tails from side to side. Like dolphins they most likely gave birth to like young underwater. There have been several wonderfully preserved specimens from the Early Jurassic of Germany actually showing young in the process of being born, the mother probably died while birthing (Benton).

Pleaiosaurs

members of the order Plesiosauria. A marine reptile, ranging from 2-14 m in body length, with powerful paddle-like limbs that probably were used to propel it thru the water. They were a major sea predator during the time (Benton).

Archaeopteryx

a medium sized bird, with a curved neck and a long straight tail (Benton, 1990). Considered fossle of earliest bird. Most famous fossil found in West Germany.

Ammonites

a group of fossil cephalopod mollusks that had a spiral shell (similar to a Nautilus) (Hale)

Cycads

a group of plants that look (at least the large ones) like palm trees with stout stems. There are no branches arising from the trunk with leaves arranged spirally at the crown. Plant reproduces by producing cones, either male or female cones are borne by a plant, not both. (Stewart, 1983)

Glossopterids

extinct group of plants with tongue-shaped leaves (over 50 species described). Glossopteris was a large tree, leaf attachments in whorls or spirals (Stewart, 1983).

Literature cited

• Benton, Michael J. Vertebrate Palaeontology. Unwin Hyman Ltd, London. 1990.
• Chatterjee, Sankar. The rise of birds: 225 million years of evolution. The Johns Hopkins University Press, Ltd., London. 1997. Chapter Five.
• Cleal, Christopher J., Barry A. Thomas. Plant Fossils: the history of land vegetation. The Boydell Press, UK. 1999.
• Clobert, Edwin H. Evolution of the vertebrates 2nd ed. John Wiley & Sons, Inc., New York. 1969.
• Condie, Kent C., Robert E. Sloan. Origin and Evolution of Earth. Prentice-Hall , Inc. Upper Saddle River, NJ. 1998.
• Cooper, John D., Richard H. Miller, Jaqueline Patterson. A trip through time: principles of historical geology. Merrill Publishing Company, Columbus OH. 1986.
• Cowen, Richard. History of Life 3rd ed. Blackwell Science Inc., Mass. 2000.
• Fastovsky, David E. and David B. Weishampel. The evolution and extinction of the dinosaurs. Cambridge University Press, Cambridge. 1996.
• Hale, W.G. and J.P. Margham. The Harper Collins Dictionary of Biology. HarperCollins Publishers, New York. 1991.
• Hallam, A. Jurassic Bivalve Biogeography." Paleobiology, Vol. 3, No. 1. (Winter 1977), pp. 58-73.
• Hallam, A. and P.B. Wignall. Mass Extinctions and their aftermath. Oxford University Press, Oxford. 1997.
• Paduan, Evin ed. The Beginning of the Age of Dinosaurs. Cambridge University Press, Cambridge. 1886.
• Stewart, Wilson N. Paleobotany and the evolution of plants. Cambridge University Press, New York. 1983.
• Upchurch, Paul. "The Evolutionary History of Sauropod Dinosaurs" Philosophical Transactions: Biological Sciences, Vol. 349, No. 1330. (Sep. 29, 1995), pp. 365-390.
• Ziegler, Alfred M., Michael Parrish, Yao Jiping, Eric D. Gyllenhaal, David B. Rowley, Judith Totman Parrish, Nie Shangyou, Andrew Bekker, Michael L. Hulver. "Palaeoclimates and their Modeling with Special reference to the Mesozoic Era." Philoshopical transactions: Biological Sciences, vol. 341, No. 1297. (August 28, 1993), pp. 297-305.

Links to other sites

• University Of California Museum of Paleontology site

• Jurassic Period
• Paleontological museum, University of Oslo, Norway
• Planetzoom
• Jurassic Source Home Page