Southern fauna of the Cretaceous

The southern Fauna of the Cretaceous was dominated by the dinosaurs whereas, at this period, the Australia and the the Antarctic formed one continent relatively isolated from the rest of the world. Many fossils were discovered on the sites of Dinosaur Cove and Flat Rocks in the south of Australia.

Formation of the continents

See also: Natural history of Australia

Formerly, Australia belonged to supercontinent Gondwana which included the southernmost whole of the emerged grounds whereas the Laurasia gathered the grounds of North.

160 million years ago (with the Jurassic superior), Gondwana starts to be divided when a Rift separates India.

125 million years ago, India is detached entirely from Africa.

Then, there are 80 million years, it is with the turn of the southern block - containing the New Zealand, Australia and the Antarctic to be detached.

At the beginning of the Cenozoic the Australian block and New Guinea separate gradually while moving towards the east.

Approximately 50 million years ago, Australia separates from the Antarctic.

For almost all this period, most of these grounds was located inside the Cercle the Antarctic and the climate of these areas was very different from the current climate. There were a flora and a single fauna for the time that one can find in the layers of fossils of Dinosaur Cove and Flat Rocks on the coasts of the south-east of Australia.

Climate

See also: Climatology, Paleoclimate

The average temperature of the southern zone was higher with the Crétacé inferior than it is it today. Several methods were employed to deduce it.

The technique which consists with evaluated the variation of the oxygen isotopes in the rock during time makes it possible to evaluate temperatures annual for the Hudson Bay around 0°C and 8°C for Toronto. The fossils of Mammalian S and Dinosaure S are enchased in rocks formed starting from the Pergélisol. That suggests that the temperature was to be around -2 to 3 °C.

The method which consists in deducing the climate from the Pollen S of plant suggests that the average temperatures should be at approximately 10°C. with cold seasons and rainy seasons. The plants in questions are Conifère S, Ginkgoales , Fougères, Cycadales , Bryophyte , Prêle and some plants with flowers. A large inland sea was to modify the climate of the area.

The distribution of the grounds was to modify the oceanic currents and to thus protect the continent from too low temperature come from the south pole. The paleoenvironmental studies let think that no Icecap extended on the entity formed by these two continents and that this one was covered with drills until its extreme south.

However, the axial slope of the Ground implies that the areas inside the Antarctic circle underwent a polar Nuit six months, i.e. that only the most robust species could survive cold and at the night. This combination of factor is not currently any more known on Earth.

Fauna

The southern zone knew already at the time, of many animals endemic, the giant Amphibians like the Temnospondyli and Koolasuchus, with the abrit their competitors Crocodilien S which could not live in areas also cold.

Mammalian S, including Monotrème S were also found. Fragmentary remainders of Ptérosaure S wheels, teeth of Plésiosaure S (marine reptiles) were also found, suggesting that they lived in rivers of the old continent. The fossils of Dinosaure are rare in Australia, but the greatest number of found fossils date of the Cretaceous, they are Allosaurus, Ornithomimosaure S, Ankylosaure S. the Hypsilophodontidae form the most common group and the most various overdraft up to now. They provide us invaluable information as for the characteristics of the dinosaurs which lived in these polar environments: they had large eyes, the openings of the optical lobes of the Crâne S were also increased. This indicates that they were adapted to the Vision of night, in sectors or the night could lasted several week.

In 1991, paleontologists discovered the first species of dinosaur of the Antarctic, the Cryolophosaurus ellioti . Some estimate that this fauna, accustomed to live in the cold and without light could have resisted the Extinction of the Cretaceous.

If the fossils of Lightning Ridge, in News-Wales of the South suggest that there is 110 million several species of Monotrème was present, the scientific community thinks that no marsupial lived there. Indeed the oldest fossils of marsupials go back only from the Paléogène and more precisely to 55 million year.

Aves

dinosaurs of the cretaceous

to see too

Related articles

Sources

  • Long, J.A., Dinosaurs off Australia and New Zealand , UNSW Close 1998

External bonds

  • Dinosaur trackways in Western Australia
  • Polar dinosaurs in Australia
  • Monash Science Centers
  • Some dinosaurs Australian
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