MESOZOIC the DINOSAURS
from the Dinosaur Collector
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The Mesozoic starts in the Early Triassic 248 million years ago. The Early Triassic is dominated by the plants and animals that had survived the Late Permian extinction. The Middle Triassic is a period of transition as dicynodonts and cynodonts whose ancestors dominated the Late Permian decline and archosaurs the ancestors of dinosaurs and crocodiles experiment with a variety of plant eating and carnivorous forms. Archosaurus become the leading predators by the middle Triassic. Dinosaurs do not show up until the Late Triassic with the start of the cycadoid conifer flora that replaces the remaining Paleozoic flora. The world continent Pangaea was still intact without major impediments to movement of animals population. The climate was characterized by extreme aridity alternating with megamonsoons. Prosauropods and small ceratosaurs being the best known dinosaurs but there are lots of other interesting creatures. The last of the archosaurs and dicynodonts die out in the final extinction at the end of the Triassic leaving the dinosaurs to fill the the world. The best information about the Triassic Dinosaurs comes from South America with Argentina producing most of the early finds.Speculation about low oxegen levels may be the key to the dominance of dinosaurs at this time. The avian style lung systems would have been a major advantage. Large size is an advantage in todays deserts and with flora of low fund value. The tailed Rhamphorynchoids appeared in the Triassic and flourished until the Late Jurassic. Eoraptor is considered the most primitive dinosaur and close to the ancestor of the whole family. Pisanosaurus the earliest known ornithiscian also is from South America. In Europe Triassic finds are scrappy. In Africa, Madagascar has produced interesting finds. The earliest known prosauropods have been reported there but have not yet been described. The earliest sauropods, Isanosaurus in Thailand and the current oldest Antetonitrus ingenipes from South Africa show up in the Triassic. Some combination of climate and flora seems to have favored the prosauropods. Sauropods don't take off until the Middle Jurassic when climate and plants change. BBC produced Walking with Dinosaurs with a an excellent graphics the Triassic installment was called the New Blood. The Triassic Seas were a time of great change as the great families of aquatic reptiles evolved. During this time the modern sea fauna is established.
The Early Jurassic and Middle Jurassic periods 206 - 159 million years ago are relatively unknown. Prosauropods start out still dominating in the Early Jurassic to be replaced by sauropods in the Middle Jurassic. Cycadoids along with ferns and conifers are wide spread through the Early Jurassic but in the Middle Jurassic cycadoids start to become less common. Conifers get much bigger and cycads are more prominent and the climate gets wetter as Pangaea starts to break up. The first armored dinosaurs appear, the first big meat eaters also show up. The first large theropods show up Dilophosaurus, Megalosaurus and Crylophosaurus. Smaller therapods like Syntarsus similar to Coelophysis are still common. The Kayenta Formation of North America gives us a window into the Early Jurassic but there are no Middle Jurassic sites in North America.. While Europe and recently China has produced the best known Middle Jurassic dinosaurs. Argentina has recently produced some major sites that should throw light on the changes in the Middle Jurassic. There are few good Middle Jurassic formations so our knowledge of this transitional period is very limited
.The Late Jurassic 159 - 144 million years ago is the Golden age of the Giant Sauropods. Brachiosaurus, Barosaurus, Diplodocus and Camarasaurus roamed North America, Europe and Africa. There is still a fashion for portrayals of Brontosaurus and other Marx style classic figures even new figures are created in the Retro Classic Style. The time of the giant redwoods and sequoias. Ferns and cycads populate the under story. The Giant Sauropods Seismosaurus, Ultrasaros and Supersaurus have been found in Western North America. The large theropods Allosaurus, Ceratosaurus and Torvosaurus are the top predators. Stegosaurs reach their greatest diversity living in Europe, Africa, Asia and North America. The Walking with Dinosaurs documentary has a a segment featuring the life of a young sauropod in North America. The Morrison formation in North America and the Tendaguru dig in East Africa have produced extensive fossil finds showing that a cosmopolitan character of the dinosaur fauna. In China different families develop suggesting a degree of isolation. Giants continue to develop in the Seas of the Jurassic. Liopleurodon was a giant of the Jurassic sea. Fish, sharks and ammonites continue to evolve. The first documented birds are found in Europe at Solenhofen along with other small dinosaur fauna. Pterodactyls start to replace the rhamphorrynids. At the the end of the Jurassic the continents have separated and new plants begin to join the conifers, ferns and cycads.
In the Early Cretaceous 144 - 99 million years ago,
Pangaea breaks up
and the plants start to change with the first flowering plants starting to
appear. Conifers and and ferns are still common and wide spread.. Iguanodons diversify and become wide spread
becoming the characteristic herbivore in the North
America, Europe and English Wealden formation . Relatives of Brachiosaurus are still found. A fragment of the
Jurassic lingers on in the
The Late Cretaceous 144 - 99 million years ago, is the final era of the Mesozoic. Flower plants are wide spread in the the northern continents of Laurasia. This is the most diverse period for dinosaurs. This diversity peaks in the North American Campanian with the Judith River fauna during the . In China and Mongolia desert communities of small theropods with bird like characteristics have been discovered. Our best picture of Gondwana is from the Neuquenian of South America.
Originally portrayed as sluggish dull creatures in the 1950's figures ,dinosaurs are now created in active poses with colorful skins. There is an audience sill nostalgia for the classic dinosaur art of Zallinger, Burien and Knight. The Early Maastrictian is represented by the Kirtlandand Horse Shoe faunas. By this time flower plants are the major players in the world. In China desert environments like Flaming Clifts and Ukhaa Tolgod perserve the smaller faunas. Therizinosaurs are unique plant eaters. The last of the dinosaurs are know from the Hell Creek formation in North America famous for Tyrannosaurs and Triceratops. There is some debate about how representative this is of the dinosaurs world wide. Reptiles continued to rule in the Cretaceous Seas and Pteranodons fly the Mesozoic Skies until the end of the Cretaceous.