245 million to 65 million BP : Triassic to Cretaceous

 

 

 

       The Mesozoic Era begins with the Triassic Period around 245 million years ago. As part

of Pangaea, this area now endured a warm, arid climate and was mostly nondepositional,

erosive, and near the equator. Around 230 million BP, the dinosaurs appear. By 228 million

BP, Eoraptor was stalking Argentina. 225 million years ago, the Petrified Forest of Arizona

grew beneath a night sky that looked much the same as today, that being the length of time

it takes the sun to orbit the Milky Way. Waterbugs, the caddis fly, crayfish, shrimps,

crocodiles, and early mammals appear during the Triassic. Around 214 million years ago,

toward the end of the Triassic Period, a large asteroid entered the atmosphere, split into

at least three large pieces, and left craters in France, eastern Canada, and Manitoba, Can.,

and around 210 million BP, another global mass extinction occurred removing 23% of living

families. Among others, the mammal-like reptiles and most crocodile-like reptiles died off.

After that, the dinosaur population and variety exploded.

       208 million BP marks the beginning of the Jurassic Period. 200 million years ago

Pangaea splits as North and South America begin to separate from Africa, North

America from Europe, and Antarctica from Africa. The early Jurassic was a period of

low relief, called the Gondwana planation, it is now seen only as the highest plateaus.

Around 180 million years BP, a large asteroid hit Mars and the impact may have thrown

bits of the planet beyond its gravity well possibly becoming some of the Martian meteorites

found on earth. Early to middle Jurassic global temperatures remained high as this area

experienced an arid and hot climate near the Tropic of Cancer. The middle Jurassic was a

geologically active period which produced the Sierra Nevada Mountains and was accompanied

by a surge in gigantism in the dinosaurs. Brontosaurs, megalosaurs, and Seismosaurus

roamed. Around 150 million BP, Archaeopteryx, the earliest bird-like form, appeared. Linear

magnetic anomalies have been used to determine the past positions of the continents back

to 150 million BP. Late Jurassic global temperatures were a little less warm, and this

area had moved above the Tropic of Cancer. By the end of the Jurassic wide ocean channels

existed at the earlier supercontinental splits and the huge sauropods (brontosaurus type)

dwindled in North America as the duckbills and ceratops rose in prominence. During the

Jurassic Period the seed ferns died out, the Sequoias were born, the Nemertea order was

created, and frogs, squid, cuttlefish, sting rays, lobsters, sea turtles, plesiosaurs,

stegosaurs, pterodactyls, and the triconodont mammals appeared.

       The Cretaceous Period began around 146 million years ago. At the very beginning,

Diplodocus, a 65-88 ft. sauropod still roamed western North America. By 140 million

years ago, at least some spiders were spinning radial webs. Worldwide temperatures

rose again during the early Cretaceous and this area reached near its' current latitude.

From early to middle it was in another period of low relief called the Kretacic planation,

seen now as high plateaus. Late in the early Cretaceous deposits are found the earliest

angiosperm pollen. By 130 million years ago the flowering plants had spread throughout

the world. 120 million years ago a superplume occurred in the Pacific Ocean, while in China,

Sinosauropteryx, a bird-like dinosaur existed. 115 million years ago a shrew-sized mammal

lived in Australia and by 110 million BP, Brazil had sea turtles and Australia had

Leaellynasaura, a turkey-sized dinosaur.

        The middle Cretaceous held an active period with widespread vertical uplift. From

100 million year old deposits we have well preserved fish in Brazil, dinosaurs in the

Patagonia of Argentina, tiny birds at Spain, a 36 ft. spinosaur (crocodile-like) in the

Sahara, and the oldest marsupial at central Utah. 95 million years ago an early water

snake which still possessed one inch long rear legs lived on the West Bank of the

Jordan River.

        In late Cretaceous deposits of Patagonia, sauropod eggs have been found with the

embryos and skin clearly seen. 80 million year old deposits in central Asia have revealed

flightless birds, and have left a site in the Gobi Desert in Mongolia with oviraptor

remains with its eggs, dromeosaurs, early mammals, lizards, turtles, and crocodiles.

75 million years ago, Tyrannosaurus Rex lived near Alberta, Canada, Maiasaura lived in

Montana, the Rocky Mountains began to rise which continued at intervals into the early

Cenozoic, and sea levels rose, flooding low-lying areas and creating an inland sea on North

America.


The last Pangean planation occurred from late Cretaceous into mid-Cenozoic

times - called the Moorland Planation or Schooley peneplain, it is now seen as plained

uplands. Concurrent with this planation was widespread volcanism. During the late

Cretaceous, diatoms evolved, duckbills were the most common dinosaur in North America,

and Pteranodon ingens evolved. 70 million years ago the placenta was introduced among

mammals, and 67 million years ago a T. Rex, later named Sue, lived in South Dakota while

the Grand Tetons rose further west.

       Late in the Cretaceous Period, the Ozarks were uplifted as the Great Plains and

Mississippi Valley regions were inundated by the sea. Isolated by hundreds of miles from

other flora, some species split from ancestral stock or became localized to this area,

possibly including Castanea ozarkensis and Hamamelis vernalis. Other flora probably existing

here at that time include the Acer (maple f.), Celtis (elm f.), Populus (willow f.), Juglans

(walnut f.), Fagus (beech f.), Sassafras (laurel f.), Rhamnus (buckthorn f.), Bumelia

(buckthorn f.), Quercus (beech f.), Magnolia (magnolia f.), Liriodendron (magnolia f.), Cornus

(dogwood f.), Diospyros (persimmon f.), Liquidambar (witch-hazel f.), Sapindus (soapberry f.),

and Gymnocladus (pea f.). Mosasaurs, fish, and toothed swimming birds inhabited the

seas to the west of us, and batlike flying reptiles appeared in the skys.

       The Cretaceous Period also produced the chrysophyceae and silicoflagellata protozoans,

the archeomonads, the Phylactolaemata Class of bryozoa, the octopods, tarpons, salmon,

trout, Triceratops, mosasaurs, and Giganotosaurus - a T. Rex type and the largest of

predatory dinosaurs to exist, placentals and opossums, and poplar, sassafras, sycamores,

magnolias, oaks, maples, elms, willows, palms, and eucalyptus. The Cretaceous Period saw

North America moving west, and the Pacific plate moving north.

       The Cretaceous Period and the Mesozoic Era ended with a literal 'bang'. 65 million

years ago the Yucatan Peninsula in Mexico was apparently hit with a large asteroid or

comet, superplumes are theorized, there was extensive volcanism occurring, and a

deposit rich in iridium appeared. Apparently these or other occurrences produced an

uninhabitable climate which culminated in the extinction of 17% of living families and

66% of all living species, notably the ammonites and the dinosaurs, whose final leavings

are 65 million year old bipedal footprints in Argentina and T. Rex coprolites in southwest

Saskatchewan.

 

                                  ___________________

 

REFERENCES

 

    Doyle, P., 1996, Understanding Fossils, An Introduction to Invertebrate

         Paleontology. John Wiley and Sons

    Fenton, C.L., Fenton, M.A., 1958, The Fossil Book. Doubleday

    Kansas Geological Survey, The Geologic History of Kansas

    King, L.C., 1983, Wandering Continents and Spreading Sea Floors on an Expanding

         Earth. John Wiley and Sons

    National Geographic Magazine

    Paleomap Project

    Stearn, C.W., Carroll, R.L., Clark, T.H., 1979, Geological Evolution of North America.

         John Wiley and Sons

    Steyermark, J.A., 1959, Vegetational History of the Ozark Forest. University of

         Missouri Studies, vol.31

    Tschudy, R.H., Scott, R.A., 1969, Aspects of Palynology. John Wiley and Sons

 

 

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