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Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
Triassic-Jurassic Periods
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Triassic-Jurassic Periods

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Triassic: Facies, Muschelkalk, Keuper,Tectonics and Paleoclimate, Triassic-Jurassic boundary, Jurassic--Lias-Black Jura, Dogger-Brown Jura, Malm -- White Jura, Belemnites, Ammonites, Reptiles

Triassic: Facies, Muschelkalk, Keuper,Tectonics and Paleoclimate, Triassic-Jurassic boundary, Jurassic--Lias-Black Jura, Dogger-Brown Jura, Malm -- White Jura, Belemnites, Ammonites, Reptiles

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  • 1. Introduction to the Mesozoic Era 248 to 65 Million Years Ago
  • 2. • The Mesozoic is divided three time periods: • the Triassic (245-208 Million Years Ago), • the Jurassic (208-146 Million Years Ago), and • the Cretaceous (146-65 Million Years Ago). • Mesozoic means "middle animals", and is the time during which the world fauna changed drastically from that which had been seen in the Paleozoic. • Dinosaurs, which are perhaps the most popular organisms of the Mesozoic, evolved in the Triassic, but were not very diverse until the Jurassic. Except for birds, dinosaurs became extinct at the end of the Cretaceous. • Some of the last dinosaurs to have lived are found in the late Cretaceous deposits of
  • 3. • The Mesozoic was also a time of great change in the terrestrial vegetation. • The early Mesozoic was dominated by ferns, cycads, ginkgophytes, bennettitaleans, and other unusual plants. • Modern gymnosperms, such as conifers, first appeared in their current recognizable forms in the early Triassic. • By the middle of the Cretaceous, the earliest angiosperms had appeared and began to diversify, largely taking over from the other plant groups.
  • 4. Or click on a subdivision of the Mesozoic to visit its exhibit! The chart at left shows the three major subdivisions of the Mesozoic Era. This chart is mapped to take you to each of these subdivisions. The Mesozoic Era occurs between the Paleozoic and the Cenozoic. 
  • 5. Mesozoic Era: Stratigraphy
  • 6. Mesozoic Era:Life The following are examples of Mesozoic life... Dinosaurs and other archosaurs, such as the pterosaurs, dominated the land biota. . . such as these dinosaurs from the Cretaceous of Mongolia
  • 7. Cycads and Bennettitaleans were among the dominant land
  • 8. • The first mammals also arrived on the scene in the Mesozoic,descended from a lineage of so-called "mammal-like reptiles," or synapsids. This is Thrinaxodon, an extinct relative of mammals from the Triassic
  • 9. Mesozoic Era: Localities Mesozoic localities on this server: (see map above) Blue Nile Gorge, Ethiopia - Come along on a fossil-hunting trip to Ethiopia with UCMP researchers and see the first dinosaur fossils from Ethiopia. Clayton Lake, New Mexico - One of the most extensive and best preserved dinosaur trackways in the United States is this Cretaceous site. Ischigualasto, Argentina - The best-known and best-preserved early dinosaurs come from this Triassic locality in South America. Karoo Basin, South Africa Pt. Loma Formation, California - This Cretaceous locality has yielded important fossils for understanding western North American dinosaurs. Saurian Expedition of 1905 - This expedition to the West Humboldt Range in Nevada is known for remarkable finds of Jurassic ichthyosaurs, and the site has since become part of Berlin-Ichthyosaur State Park. Solnhofen Limestone, Germany - Exquisitely detailed fossils have come from these Jurassic deposits in southern Germany. Triassic deposits are known from one locality in Egypt, Arif- El-Naqa dome, Sinai. Fossils As Plicatula, Myphoria, , Triassic in Egypt:
  • 10. • Duration: about 32 million years • Maximum thickness:30,000 feet • The Triassic Period (from three-fold division in Germany) spanned the time from approximately 250 million years ago until 202 mya, and it begins the Mesozoic Era. Life forms in this time are significantly different to those that lived prior to the mass extinction at the end of the Permian. • This system represents the first period in the Mesozoic . The physical conditions of depositions remined much the same as in the Permian times but we get different organic remains. Plants became varied. • The name " Trias" was given to this group of rocks by Von Alberti in 1834 from three-fold division in Germany. The three divisions are also found in the Vosges as follow:- 1-Varigated sandstone or BuntSand stein. 2-Shelly limestone or Muschelkalk. 3-Varicolored marl or Keuper. The Bunter and Keuper are continental facies , found in Europe in the(N.R.S.St.) except in the Alpine chains. • In the Middle Triassic an epicontinental sea of the Mushelkalk occupied central Germany and Vosges , while in the eastern Europe, Alps.etc., there was a geosyncline with thick deposits • In the oceans, the ammonoids were predominant survivors into the Mesozoic. On land, the condonts arose in the Early Triassic,
  • 11. Triassic: Facies   TheTriassic shows considerable development of both continental and marine  The Bunter series (Buntsandstein): consists chiefly of red beds  such as conglomerates, sandstones and shales with some salt and gypsum. They  indicate deposition under desert, arid climatic conditions. These series seem to have  deposited in German and in the interior of United  States at the same time.  The Muschelkalk series is mostly a marine limestone formation, thus  showing the presence of marine waters over the German region. The Keuper (Rhaetic),conditions of depostion on were much as during the Bunter ( continental facies beds). though late keuper marine water again transgressed  the area .  
  • 12. The Triassic in Germany:- 1- BuntSandstein : It consists of continental or lagoonal sediments , conglomerate, sandstone,shale...violet and red in colour. Its top shows more or less marine facies, with Myophoria forming a passage to the next stage. 2- Muschelkalk : It is divided into the following units: a- Lower corrugated limestone with Terebratulla vulgaris, Myophoria, Lima,.. b-Anhydrite group : marly, dolomitic with gypsum, anhydrite. c- Muschelkalk proper: marine facies with crinoid (forming the know crinoidal limestone), Ceratites nodosus, Myphoria vulgaris 3- Keuper(Rhaetic) time: It consists of upper Keuper or Rhaetian , Middle Keuper and lower Keuper.This stage shows saliferous formations with green or red marls gypsum, anhydrite and sandstone with plants remains. Subdivision of the Triassic:- Germany Upper Triassic -----------------------Keuper. Middle Triassic-----------------------Muschelkalk. Lower Triassic------------------------BuntSandstein
  • 13. Significant Events  Life Restarts • Ninety-six percent of all species vanished at the end of the Permian. The subsequent opening of niches provided a wonderful opportunity for new life forms in the Triassic. During this period we see the rise of the conodonts and their descendants, the dinosaurs and birds, and also the rise of mammals.  Pangaea  During the Permian all land masses were congregated into a single equatorial supercontinent known as
  • 14. Triassic Graphics  Triassic View  Plateosaurus
  • 15.    Yaleosaurus
  • 16. The Triassic Period 248 to 206 Million Years Ago• In many ways, the Triassic was a time of transition. It was at this time that the world-continent of Pangaea existed, altering global climate and ocean circulation. • The Triassic also follows the largest extinction event in the history of life, and so is a time when the survivors of that event spread and recolonized. • The organisms of the Triassic can be considered to belong to one of three groups: holdovers ‫المتبقين‬ from the Permo-Triassic extinction, new groups which flourished briefly, and new groups which went on to dominate the Mesozoic world. The holdovers included the lycophytes, glossopterids, and
  • 17. • Subdivisions of the Triassic: • The chart at left shows the major subdivisions of the Triassic Period. Click to go forward to the Jurassic, or back to the end of the Paleozoic Era, the Permian Period. • The Triassic Period is part of the Mesozoic Era. 
  • 18. Triassic Period: Stratigraphy • Subdivisions of the Triassic: • The chart at left shows the major subdivisions of the Triassic Period. The youngest stage, the Rhaetian, is found only in the vicinity of the Alps, in Europe, and so some workers feel that it does not deserve global recognition. • This chart is mapped. Click to go forward to the Jurassic, or back to the end of the Paleozoic Era, the Permian Period. • The Triassic Period is part of the Mesozoic Era. 
  • 19. Triassic Period: Localities
  • 20. • Localities for Triassic fossils are rare for the Early and Middle portions on the Period, but more common for the Late Triassic. Localities fall into one of two broad regions, corresponding roughly with the northern and southern hemispheres, with India belonging to the latter. • Triassic localities on this server: (see map above) • Chinle Formation, Arizona • Ischigualasto, Argentina - The best- known and best-preserved early dinosaurs come from this locality in South America.
  • 21. Triassic in Egypt: Triassic deposits are known from one locality in Egypt, Arif- El-Naqa dome, Sinai. Fossils As Plicatula, Myphoria, , Ceratites
  • 22. Triassic Period:Tectonics and Paleoclimate • The Triassic period was a transition from the Paleozoic Era to the Mesozoic. It is situated between the end of the Permian period and the beginning of the Jurassic, lasting from 254 mya to 206 mya. As with almost any other period of the Earth's history, the Triassic had a unique climate and biota indigenous to that time. The paleoclimate was influenced largely by tectonic events that never existed before or since.
  • 23. • At the beginning of the Triassic period, the land masses of the world were still bound together into the vast supercontinent known as Pangaea. Pangaea began to break apart in the mid-Triassic, forming Gondwana (South America, Africa, India, Antarctica, and Australia) in the south and Laurasia (North America and Eurasia) in the north. The movement of the two resulting supercontinents was caused by sea floor spreading at the midocean ridge lying at the bottom of the Tethys Sea, the body of water between Gondwana and Laurasia. While Pangaea was breaking apart, mountains were forming on the west coast of North America by subduction of the ocean plates beneath the continental plates. Throughout the Middle to Late Triassic, mountain forming continued along the coast extending from Alaska to Chile. As mountains were forming on the Americas, North Africa was being split from Europe by the spreading rift. This division of the continents advanced further westward, eventually splitting eastern North America from North Africa
  • 24. • The climate of the Triassic era was influenced by Pangaea, its centralized position stradling the equator, and the geologic activity associated with its breakup. Generally speaking, the continents were of high elevation compared to sea level, and the sea level did not change drastically during the period. Due to the low sea level, flooding of the continents to form shallow seas did not occur. Much of the inland area was isolated from the cooling and moist effects of the ocean. The result was a globally arid and dry climate, though regions near the coast most likely experienced seasonal monsoons. There were no polar ice caps, and the temperature gradient in the north-south direction is assumed to have been more gradual than present day. The sea level rose as the rift grew between North Africa and southern Europe, resulting in the flooding of Central and South Europe; the climates of terrestrial Europe were hot and dry, as in the Permian. Overall, it appears that the climate included both arid dune environments and moist river and lake habitats with gymnosperm forests.
  • 25. • Some conclusions can be drawn about more specific regional climates and species based on experimental research. The presence of coal-rich sequences in the high northern and southern latitudes, as well as the presence of large amphibians there, indicates that the paleoclimate was wetter in those areas. Living species of some Mesozoic ferns (including the families Osmundacae and Dipteridacae) now live in wet, shady areas under forest canopies, so it is likely that the paleoclimate their Triassic ancestors inhabitted were also damp and shaded. The Mesozoic era might also have had large, open areas with low- growing vegetation, including savannas or fern prairie with dry, nutrient poor soil populated by herbaceous plants, such as ferns of the families Matoniaceae and Gleicheniaceae. Thus, despite the union of the continental landmasses, the Triassic vegetation was quite provincial, though this decreased as the Triassic wore on. The northern forests at the beginning of the Triassic were dominated by conifers, ginkgos, cycads, and bennettitaleans, while the forests of Gondwana were dominated by Dicroidium and Thinnfeldia. By the end of the Triassic, both hemispheres gave way to conifer and cycad vegetation
  • 26. • The Triassic-Jurassic boundary is similar to the Permo-Triassic boundary in that the global climate was not radically altered, though a major extinction of terrestrial vertebrates occurred. • With the end of the Triassic and the beginning of the Jurassic, Pangaea continued to break apart, inevitably ‫حتما‬ affecting the climate, though not as radically
  • 27. • Flora: Age of Cycades (Conifers, Ferns, Sigillaria). Voltzia heterophylla (Age of Cycades) Invertebrates: Sponges and Coelenterates: Corals limestone (hexacorals)developed. Tetracorals disappeared, Stromatoporids persist till the Cretaceous. Brachiopods: Rhynchonellas and Terebratualas more developed Myophoria vulgaris Ceratites nodosus Phylloceras Vertebrates Reptile :Teleropeton Swimming Reptiles,Mammals.  Triassic : Climate: • Arid to semi-arid , rather hot and dry , climate seems to have been remarkably widespread during the Trissic. • The widespread distribution of salt and gypsum adds further evidence for a widespread aridity.  Life of the Triassic
  • 28. All fossils in the Triassic Monotis Ceratites humboldtensis 1998
  • 29. Owenites koeni © 2004 Paratropites antiselli © 2005
  • 30. Sagenites © 2004 Scleractinian © 1998
  • 31. Phytosaurus tooth © 2005 Shastasaurus pacificus © 2004
  • 32. Shonisauru s popularis © 2004 Planolites © 2003
  • 33. Stegomus arcuatus © 2005 Phytosauridae © 2003
  • 34. Minor Extinctions of Earth History Although mass extinctions are most studied by the paleontological community, several smaller-scale extinctions have also been documented. • These extinctions, occurring in the Triassic, Jurassic, Oligocene, and Neogene, did not affect as many species as the major mass extinctions, but are critical to understanding the patterns of extinction. • The Triassic Extinction • Labyrinthodont amphibians, conodonts, and all marine reptiles(excluding ichthyosaurs) were eliminated and mammal-like reptiles, thecodonts, brachiopods, gastropods, and molluscs were severly affected by this event. • The causes of the Triassic extinction are not well known, but popular explanations for its occurrence include global climatic cooling, extra-terrestrial impact, or comet showers. This extinction event is particularly important because it allowed the
  • 35. • Duration: about 57 million years • Maximum thickness: 44, 000 feet • The Jurassic formations were first known in the Jura Mountains between France and Switzerland ( from which the name of the system was derived). • During the Jurassic, North and South America, Africa, and Australia were joined in a supercontinent near the equator. Europe and Asia had just broken off from the Pangean supercontinent. • There are few outcrops of Jurassic rock in North America, but the best-known of Jurassic strata, the Morrison Formation, is found in much of the Western interior of the U.S. It was during this time that the huge sauropod dinosaurs such as Apatasaurus and Brachiosaurus lived. • Sea level was low but rising during the Early Jurassic, and high throughout the remainder of the
  • 36. JURASSC SYSTEM    Facies There are two distinct types of facies : marine and non-marine (continental(: In the Northern Hemisphere: Marine marls and limestones that are often oolitic are deposited as a result of submergence of the great salt lakes and other basins.The marine transgression of the late Triassic time continued into the Jurassic. In the Southern Hemisphere : continental facies consisting of sandstones and shales are well developed.  In Jura Mountains, the Jurassic is divided into: 1-Black Jura 2-Brown Jura 3- White Jura This division corresponds to Subdivision of the Jurassic:  Lower Jurassic----------------------------Lias- Black Jura Middle Jurassic ---------------------------Dogger-BrownJura Upper Jurassic----------------------------Malm -- White Jura Oppel divides these formations into 33 biostratigraphic zones of Ammonites .Later, the number of these zones was greatly
  • 37. Significant Events  Continental Breakup • The Permian-Triassic supercontinent of Pangaea began to break apart in the Jurassic, with the splitting off of the European-Asian component.  Himalayan Deposition • The rocks that would ultimately become the highest point on Earth were deposited in the Triassic and Jurassic Periods as limestones, dolomites, and shales.
  • 38.  Rhamphorhynch us  Stenopterygiu s Jurassic Graphics
  • 39.  Allosaurus  Allosaurus
  • 40.  Shrimp  Sectioned Ammonite
  • 41. Plesiosaur Plesiosaur
  • 42. Horseshoe Crab Bone Bed
  • 43. Morrison Formation
  • 44. • Great plant-eating dinosaurs roaming the earth, feeding on lush growths of ferns and palm-like cycads and bennettitaleans. . . smaller but vicious carnivores stalking the great herbivores. . . oceans full of fish, squid, and coiled ammonites, plus great ichthyosaurs and long-necked plesiosaurs. . . vertebrates taking to the air, like the pterosaurs and the first birds. . . this was the Jurassic Period, beginning approximately 210 million years ago and lasting for 70 million years of the Mesozoic Era. • Named for the Jura Mountains on the border between France and Switzerland, where rocks of this age were first studied, the Jurassic has become a household word with the success of the movie Jurassic Park. Outside of Hollywood, the Jurassic is still important to us today, both The Jurassic Period 206 to 144 Million Years Ago
  • 45. Subdivisions of the Jurassic: The chart at left shows the major subdivisions of the Jurassic Period. This chart is also mapped to take you back in time to the Triassic, or forward to the Cretaceous. The Jurassic Period is part of the Mesozoic Era
  • 46. Jurassic Period:Stratigraphy
  • 47. Jurassic Period: Life
  • 48. Life of the Jurassic Flora: Flora: Age of Cycades (Conifers, Ferns, Cycades). Cycadeoidea microphylla  Fauna: Invertebrates:  Corals: all belong to hexacorals, no stratigraphic importance. The profusion of Corals  Braciopods, mostly of Terebratulla and Rhynconella types Trigonia monilifara, Plicatula spinosa, Cidaris florigemma Gryphaea arcuata  Cephalopods, Ammonites are the most striking features of the period, more abundant than "Belemnites" and hence term : Age of Ammonites Ammonites: Phylloceras , Harpoceras (Lower Jurassic) Cosmoceras, Aspidocras ( Midle Jurassic( Perisphinctes, Oppelia (Upper Jurassic(  Belemnites Crinoides and sea Urchins of modern aspects were all represented  Vertebrates:  Fishes and Amphibian  Reptiles , Age of Reptiles Ex. (Dino—Terrible, Saures ---Reptile)- Birds- Mammals.   Reptiles: Ichthysaurus, Plesiosaurus,Pteroidactylus, Megalosaurus
  • 49. • But there was more to life than dinosaurs! In the seas, the fishlike ichthyosaurs were at their height, sharing the oceans with the plesiosaurs, with giant marine crocodiles, and with modern-looking sharks and rays. • Also prominent in the seas were cephalopods -- relatives of the squids, nautilus, and octopi of today. Jurassic cephalopods included the ammonites, with their coiled external shells (upper left), and the belemnites, close relatives of modern squid but with heavy, calcified, bullet- shaped, partially internal shells. Among the plankton in the oceans, the dinoflagellates became numerous and diverse, as did the coccolithophorids (microscopic single- celled algae with an outer covering of calcareous plates). • Land plants abounded in the Jurassic, but floras were different from what we see today. Although Jurassic dinosaurs are sometimes drawn with palm trees, there were no palms, or any other flowering plants, at least as we know them today, in the Jurassic. Instead, ferns, ginkgoes, bennettitaleans or "cycadeoids", and true cycads -- like the living cycad pictured at the above right -- flourished in the Jurassic. Conifers were also present, including close relatives of living redwoods, cypresses, pines, and yews. Creeping about in this foliage, no bigger
  • 50. Jurassic Period: Localities Extensive Jurassic deposits can be found in the Rocky Mountains of the United States, England and western Europe, central Russia, and in many other parts of the world Jurassic localities on this server: (see map above) Blue Nile Gorge - Come along on a fossil-hunting trip to Ethiopia with UCMP researchers and see the first dinosaur fossils from Ethiopia. Saurian Expedition of 1905 - This expedition to the West Humboldt Range in Nevada is known for remarkable finds of Jurassic ichthyosaurs, and the site has since become part of Berlin-Ichthyosaur State Park. Solnhofen Limestone -Exquisitely detailed fossils have come from these Jurassic deposits in southern Germany.Jurassic in Egypt: Jurassi deposits are very well developed in :- •Maghara dome and Risan Aniza (N.Sinai) •Middle Jurassic is also exposed on the western coast of the Gulf of Suez • At Northern Galala Plateau.
  • 51. • Over much of the world, the Jurassic beds were stable , but by late Jurassic time, intense and widespread locallocal deformationdeformation took place in N. America accompanied by the intrusion of immense Batholiths of Granite. This Orogeny has been named, the Nevadian disturbanceNevadian disturbance.  Jurassic: Climate • Climate warm, equable and more humid than it had been in the Triassic. • Towards the close of the Period, climate was rather warm and moist over much of the earth. This is indicated by Dinosaures in Mangolia, where winter temperature now fall far below zero. • Dinosaures very probably could not endure freezing weather. Jurassic Orogeney:
  • 52. Life of the JurassicFlora: Age of Cycades (Conifers, Ferns, Cycades). Cycadeoidea microphylla Fauna: Invertebrates Corals: all belong to hexacorals, no stratigraphic importance. The profusion of Corals Braciopods, mostly of Terebratulla and Rhynconella types Trigonia monilifara Plicatula spinosa Cidaris florigemma Gryphaea arcuata Cephalopods, Ammonites are the most striking features of the period, more abundant than "Belemnites" and hence term : Age of Ammonites. Ammonites: Phylloceras , Harpoceras (Lower Jurassic) Cosmoceras, Aspidocras ( Midle Jurassic) Perisphinctes, Oppelia (Upper Jurassic) Belemnites Vertebrates: Fishes and Amphibian Reptiles , Age of Reptiles Ex. (Dino—Terrible, Saures ---Reptile)- Birds- Mammals. Reptiles: Ichthysaurus, Plesiosaurus,Pteroidactylus, Megalosaurus Earliest bird : Archaeoptenyx macrura The Mammalian as in the Triassic
  • 53. All fossils in the Jurassic Amaltheus stokesi 2003© Ammonite © 2003
  • 54. • Groebericeras baileyi © 2004 Bucklandia sp. © 2005
  • 55. Elatides sp. © 2005 Elatides sp. © 2005 Allosaurus fragilis © 2005
  • 56. Anchisaurus polyzelus 2005© Semionotid fish © 2005
  • 57. Buchia fisheria 2003 Seirocrinus 2003©
  • 58. The Jurassic Extinction Two extinction events are speculated to have occurred in the Jurassic. •The first of these events is recognized in Pleinsbachian age strat from Europe. This extinction eliminated more than eighty percent of marine bivalve species, along with various other shallow water species. •The second crisis occurred near the end of the Jurassic, by an event that severly affected ammonoids, marine reptiles, and bivalves. •Dinosaurs were also severly affected as stegosaurs and most types of sauropods did not survive into the Cretaceous period. This event is not well understood so few hypothese have yet been proposed for its occurrence .

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