Watch Faris Aliani’s talk:

Dinosaurs roamed the Earth during the Mesozoic era and reign supreme. They first appeared and evolved around 250 million years ago. As millions of years went by, the continents as we know them today, began to form and as the dinosaurs were isolated from each other and many unique groups evolved.

Dinosaurs are a diverse group of animals of the clade Dinosauria. They first appeared during the Triassic era, 231million years ago, and were the dominant terrestrial vertebrates for 135 million years, from the start of the Jurassic (about 200 million years ago) until the end of the Cretaceous period (66 million years ago). In 1842, paleontologist Sir Richard Owen, used the term dinosaur to refer to the “distinct tribe or sub-order of Saurian Reptiles” that were then being recognized in England and around the world. The term is derived from the Greek words deinos, meaning “terrible”, “potent”, or “fearfully great” and sauros, meaning “lizard” or “reptile”.

These beasts are generally terrestrial reptiles that have hind limbs held erect beneath the body unlike most other reptiles which have legs jutting out from their body. Many of them may have been endothermic(warm-blooded).Although large dinosaurs like the sauropods may have been ectothermic (cold-blooded) as their large size would entail immense metabolic requirements and due to their immense size it negates heat loss as it takes longer to ‘cool’ down.

Therizinosaurus are very large theropod dinosaurs. Though the fossil remains of Therizinosaurus are incomplete, but like other members of their family, Therizinosaurus probably had small skulls atop long necks. They had a herbivorous diet. Combined with its long necks & large claws this presumably allowed it to reach the tops of small tree & shrubs though it evolved from theropods the group of dinosaurs of which included the fearsome T.rex.

Spinosaurus (spine lizard) is a genus of theropod dinosaur that lived in what now is North Africa. Though original remains were destroyed in World War 2 by cross referencing fossils of close relatives the overall skeleton has been reconstructed. Spinosaurus was among the largest of all known carnivorous dinosaurs, possibly larger than Tyrannosaurus and Giganotosaurus.  It may have well been bigger than T.rex but it had a piscivorous diet. Its crocodile-like snout was well adapted for fish-hunting and the sail at its back enabled it to keep warm after catching fish.

The impact of a meteorite or comet is today widely accepted as the main reason for the Cretaceous–Paleogene extinction event 65 millions years ago. The impact would have caused  some of the largest megatsunamis in Earth’s history. A cloud of super-heated dust, ash and steam would have spread from the crater in less than a second.  The emission of dust and particles could have covered the entire surface of the Earth for several years,  creating a harsh environment for living things. The shock production of carbon dioxide caused by the destruction of carbonate rocks would have led to a sudden greenhouse effect.  Over a longer period, sunlight would have been blocked from reaching the surface, cooling the surface dramatically.  Photosynthesis by plants would also have been interrupted, affecting the entire food chain.

The extinction of the dinasours left us their fossils underneath the earth’s crust. Geologists in the late 18th and early 19th century studied rock layers and the fossils in them to determine relative age by studying their distribution through the sequence of sedimentary rocks. In the 20th century enough information had accumulated about the rate of radioactive decay that the age of rocks and fossils in number of years could be determined through radiometric age dating. Uranium-lead radiometric dating involves using Uranium-235 or Uranium-238 to date a substance’s absolute age.

Until the late 20th century, all groups of dinosaurs were believed to be extinct. However, the fossil record indicates that birds are the modern descendants of feathered dinosaurs, having evolved from theropod ancestors during the Jurassic Period, and are now termed “avian dinosaurs”. As such, birds were the only dinosaur lineage to survive the mass extinction event.

Presented by: Faris Aliani

Edited by: Hakim Morni (editor of Science For Thought,PTETYSF newsletter)

 

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