VIZUALIZING EARTH HISTORY

1. VIZUALIZING EARTH HISTORY By Loren E. Babcock Chapter 11 Mesozoic World

2. Timeline of Mesozoic events

3. Triassic Period Major marine life forms of the Triassic Period. Global sea level at the beginning of the Triassic Period was relatively low, and close to its modern position. It rose to a level perhaps 100 m above its present position, then fell again at the end of the period. Orogenies in Eurasia completed the assembly of Pangea. Large portions of Pangea, ones far from ocean waters, formed arid deserts. The high peaks of the Appalachian Mountains, which arose in the late Paleozoic, were subdued through erosion in the Triassic Period.

4. Triassic Period Triassic Marine Life Extinction at the end of the Permian Period wiped out great numbers of marine organisms (trilobites, fusulinid foraminifera, rugose corals, and lacy bryozoans), leaving a new world to be exploited by those surviving the crisis. Other groups suffered substantial declines without being completely annihilated. Recovery from the Permian extinction event was a protracted process for most marine animals other than ammonoid cephalopods and conodonts.

5. Triassic Period Triassic Marine Life Reef-forming corals, sea urchins expanded during the Triassic and Jurassic periods. Reptiles first invaded the sea during the Triassic Period. Plesiosaur - A Mesozoic marine reptile with a euryapsid skull type, a broad body, and large paddlelike limbs. Ichthyosaur - A Mesozoic marine reptile with a dolphin-like body. At the end of the Triassic Period, mass extinction occurred in marine ecosystems. The timing of extinction coincides with floral evidence for a climatic shift to arid conditions in terrestrial environments of Gondwana, and with a large drop in sea level.

6. Triassic Period Terrestrial life of the Triassic Period Land plants were little affected by extinction at the end of the Paleozoic Era. As the world entered the Mesozoic Era, gymnosperms such as ferns, conifers, cycads, and ginkgos dominated the landscape. Three land vertebrates appeared during the Early Triassic, an amphibian group (frogs), and two reptilian groups (turtles and primitive archosaurs). The group known as archosaurs includes crocodiles, phytosaurs, pterosaurs (flying reptiles), and dinosaurs. All these groups appeared in the Late Triassic.

7. Triassic Period Terrestrial life of the Triassic Period The earliest dinosaurs were small bipedal animals. It was in the Jurassic Period that dinosaurs diversified and reached large proportions. Primitive synapsids (or “mammal-like reptiles) persisted from the late Paleozoic. Fossils of one Triassic therapsid, Lystrosaurus, were helpful in matching Pangea. Mammals appeared in the Late Triassic. The early mammals remained small and inconspicuous through the entire Mesozoic Era.

8. Triassic Period Terrestrial life of the Triassic Period

9. Jurassic Period The splitting and rifting of Pangea. The Jurassic Period was a time of great change tectonically and biotically. The period opened with global sea level at one of its lowest points in geologic history. Pangea was beginning to rift apart, and both marine and terrestrial ecosystems were being reshaped. Separation of Pangea led not only to the development of the modern continents, but also to the evolution of separate biotas associated with them.

11. Jurassic Period Jurassic Marine Life In the Jurassic Period, marine predator-prey systems reached the top of the Mesozoic Marine Revolution. Swimming predatory mollusks (ammonoids) and relatives of the squids called the belemnoids appeared. These cephalopods enjoyed a varied diet including crustacean arthropods, fishes, and mollusks. Ammonoids evolved rapidly in the Jurassic and Cretaceous periods. Fishes of the Mesozoic Era were mostly carnivorous. Sharks and rays, holdovers from the Paleozoic Era, increased in number in the Jurassic and Cretaceous periods.

12. Jurassic Period Jurassic Marine Life Plesiosaurs had developed into a major threat, and they apparently had a large vertical range in the water column. Ichthyosaurs were among the top predators of Mesozoic seas. Pterosaurs, or flying reptiles, probably relied on fishes, crustaceans, and cephalopods swimming close to the water’s surface for a large part of their nutrition.

14. Jurassic Period Jurassic Marine Life Other benthic or nektobenthic carnivores included some snails and crustaceans. Brachiopods and stalked echinoderms fell into great decline, and they never again achieved more than a minor role in marine ecosystems.

15. Jurassic Period Jurassic Marine Life A group of floating algae, called the dinoflagellates, which produce durable organic cysts, emerged in the Jurassic Period as important contributors to the phytoplankton biomass. Dinoflagellates have an evolutionary history extending back to the Proterozoic Era (where some are referred to under the collective term “acritarchs”), but they achieved a more impressive diversity in the Jurassic Period.

16. Jurassic Period Terrestrial Jurassic Life Gymnosperms were the most common land plants of the Jurassic Period. Cycads, conifers, ferns, and ginkgos dotted the landscape and provided much of the food for herbivorous dinosaurs and mammals. Dinosaurs became the most conspicuous land animals of the Jurassic Period, and they remained so through the Cretaceous Period.

18. Jurassic Period Dinosaurs Inherit the Land Dinosaurs are characterized by an upright posture, carrying their legs below the body, and by having a skull with two openings behind the eye. There are two major groups, each distinguished principally on the basis of hip bone structure. Saurischian dinosaur - An archosaur characterized, at least primitively, by a lizard-like hip. Ornithischian dinosaur - A Mesozoic archosaur characterized by a bird-like hip; most species were herbivores.

19. Jurassic Period Dinosaurs Inherit the Land

20. Jurassic Period Dinosaurs Inherit the Land Saurischian dinosaurs are of two basic types: theropods and sauropodomorphs. Theropod - A clade of saurischian dinosaur having bipedal gait and, at least primitively, teeth adapted for carnivory. The clade includes birds. Sauropodomorphs - were herbivores, and basically quadrupedal. The more derived sauropods were the largest animals to ever live on land.

21. Jurassic Period Dinosaurs Inherit the Land Theropods often had long strides, meaning they could move quickly. This is consistent with the interpretation that they were endothermic, or “warm-blooded,” rather than ectothermic, or “cold-blooded,” like present-day lizards and crocodiles.

22. Jurassic Period Dinosaurs Inherit the Land Ornithischian dinosaurs, which range from the latest Triassic to the end of the Cretaceous Period, were mostly herbivores. Genera include Protoceratops, Triceratops, and others, all of which had giant bony shields covering the head and neck.

23. Jurassic Period Dinosaurs Inherit the Land Another group of ornithischian dinosaurs is the bipedal ornithopods, which include Iguanodon, the duckbills (Hadrosaurs), Parasaurolophus, Corythosaurus, and Maiasaura, among others. Nests and eggs laid by dinosaurs are known from many areas of the world. One of the most revealing discoveries is from Cretaceous strata of Montana, where nesting grounds of the hadrosaur Maisaura (literally “good mother lizard”) were rapidly buried under shifting desert sands.

25. Jurassic Period Origin of Birds The oldest known bird fossils, Archaeopteryx (literally, “ancient wing”), are from the Jurassic of Germany.

26. Cretaceous Period The origin of chalk and black shale in Cretaceous strata. During the Cretaceous Period, Pangea continued fracturing into its modern drifting continents. High sea level, greenhouse climatic conditions, driven by undersea volcanoes spewing their content, warmed the oceans beyond the tropics, and planktonic microorganisms bloomed in the seas until the end of the period. The Earth experienced a long interval of normal polarity (about 40 million years), during the mid-Cretaceous. In the 20 million years prior, quick polarity reversals (less than 1 million year intervals), were the rule, just as they had been through much of the Mesozoic Era.

27. Cretaceous Period Cretaceous Tectonics, Sea Level, and Ocean Circulation Supercontinent breakup and rifting accelerated in the Cretaceous Period. Oxygen minimum zone - Interval in a water body in which the amount of dissolved oxygen is less than that above or below it. At the end of the Cretaceous Period, beginning about 67 million years ago, sea level dropped precipitously. Oxygen isotopic ratios recorded in marine foraminifera, and a change in land plant communities in high latitudes, point to cooling of the poles.

28. Cretaceous Period Cretaceous Marine Life Sea level reached also its highest levels during the Cretaceous, and warm conditions meant that the oceans were teeming with life. Microorganisms forming the bases of food webs were major contributors to marine sediments. Diatom - Single-celled phytoplankton having an ornate microscopic skeleton (test) composed of two valves impregnated with opaline silica.

29. Cretaceous Period Cretaceous Marine Life Dinoflagellates experienced a series of adaptive radiations in the Phanerozoic Era, including in the Cretaceous Period. Chalk - Soft marine limestone composed mostly of calcitic coccolithophorid plates. Mollusks continued to evolve quickly in the Cretaceous. Rudist - A type of Mesozoic clam having unequal valve sizes that often formed reefs in the Cretaceous. Many modern snails appeared in the Cretaceous Period.

30. Cretaceous Period Cretaceous Marine Life Swimming carnivorous mollusks, the belemnoids, account for some of the most conspicuous Cretaceous fossils. Ammonoids evolved quickly during this period. Ammonite - A cephalopod having ammonitic sutures. Teleost fishes, which are the dominant group of fishes today, became prevalent in Cretaceous seas. The Cretaceous Period witnessed an arthropod predator: the modern crabs. With their claws, crabs break shells or skeletons of their prey obtaining nutritious soft tissues inside.

31. Cretaceous Period Cretaceous Terrestrial Life Dinosaurs ruled the land during the Cretaceous Period. The giant sauropods were all gone, but ceratopsians and ornithopods expanded in numbers. Carnivorous theropods also prowled the landscape. By the Late Cretaceous, the two modern groups of mammals, placentals and marsupials, had evolved, yet they remained small and inconspicuous. Flying reptiles and birds were the largest animals in the air.

32. Cretaceous Period Origin of flowering plants. Close to the Jurassic-Cretaceous transition, a group of gymnosperms gave rise to the flowering plants (angiosperms). Angiosperms have a tremendous ecological advantage over gymnosperms partly because they enclose their seeds in a special reproductive chamber (an ovary). The evolutionary success of angiosperms reinforced by their development of the flower. Showy flowers are attractive to animals, especially insects, but also birds and mammals. All of these animals help with the fertilization process.

33. Cretaceous Period End-Cretaceous Extinction The impact of a bolide from outer space at the end of the Cretaceous may have crippled ecosystems that were already in fragile condition. Streaking toward Earth 65.5 million years ago was probably an asteroid that had fallen from its orbit, finally crashing into the northern tip of the Yucatan Peninsula of Mexico. The Late Cretaceous was a time of major volcanic activity, where gases and dust were emitted that blocked sunlight. With less sunlight reaching the Earth’s surface, global temperatures should have declined.

34. Cretaceous Period End-Cretaceous Extinction Sea level dropped markedly at the end of the Cretaceous Period. Impact of the Chicxulub bolide was felt globally. Shock waves reverberated from the impact site, and dust and debris were sent high into the atmosphere. Shocked quartz - Quartz grain showing distinctive parallel sets of welded microscopic planes, called shock lamellae. The aftereffects of the Chicxulub impact, added to an already stressed ecosystem, may have been enough to drive many groups to extinction.