Monday, March 13, 2006


What are reptiles and how are they classified into different groups. How
does the morphology of these organisms affect their different survival
strategies. What happend in the cretaceous tertiary period and what were
the main causes and outcomes of this massive extinction.

Nicole Prinsloo
Biodiversity and Conservation Biology
Zoology Department
University of the Western Cape
Email : 2449162@uwc.ac.za


  • You should have described the adaptive radiation that took place and specifically the environments they invaded (land, water and air) and the morphological changes necessary for success in these environments. To illustrate the 500 word abstract below took me 15 minutes to research and compose…

    The Mesozoic (Middle Life) lasted 180 million years: from 251 million years ago (Ma) to when the Cenozoic era began (65 Ma) and is divided into three geologic periods, namely

    Triassic (248.2 Ma to 205.7 Ma),

    Jurassic (205.7 Ma to 144.2 Ma)and

    Cretaceous (144.2 Ma to 65.5 Ma).

    The Mesoic was a time of enormous climatic, and tectonic upheavals and resulted in a spectacle evolution of animal forms, most notably the reptiles. The climate was exceptionally warm favouring reptiles and the many shallow seas favoured the evolution of a wide range of aquatic forms. Of the Mesozoic life forms to have evolved the dinosaurs were possibly the most spectacular. Dinosaurs were extremely diverse, although most were actually herbivorous, the carnivorous forms such as T. Rex have captured the public's imagination. Dinosaurs included bipedal forms that were very often fast and agile hunters, and many very large, herbivorous quadrapedal forms. Modern Birds evolved from theropod dinosaurs and feathers may well have first appeared in these Mesozoic reptiles.

    Dinosaurs are divided into two major groups

    1) Saurischians ("lizard hip") forms and included the carnivorous dinosaurs (theropods} plus the long-necked, herbivorous dinosaurs that became the largest animals that ever walked the earth (Sauropods).

    2) Ornithischians ("bird-hipped") forms and were herbivores, possibly lived in herds, and were preyed upon by the theropods.

    A vast array of aquatic Mesozoic reptiles evolved and included

    1) Ichthyosaurs (Greek for "fish lizards") that resembled modern dolphins with their large teeth,

    2) Plesiosaurs which were large, carnivorous aquatic reptiles and would ecologically have similar niches to modern-day seals (some of which were huge reaching 15 m (50 ft) in length such as Liopleurodon}

    3) Mosasaurs which were serpentine marine reptiles, thought to be related to snakes.

    Mesozoic reptiles that invaded the air are termed Pterosaurs and were the first vertebrates to evolve flight. Pterosaur’s wings were formed by a membrane of skin stretching from the body to an elongated fourth digit on the hand. While most pterosaurs were of fairly modest size, some really large forms such as Quetzalcoatlus with a wingspan of 12 metres and a mass of 50 kilograms evolved.

    Many of these reptiles (including Dinosaurs) became extinct at the end of the Cretaceous period and is often referred to as the K-T extinction (K is the traditional abbreviation for the Cretaceous period). Many explanations for this event have been hypothesized. The most frequently suggested theory is the impact of a ten-kilometer-wide asteroid (there is a marine crater buried under Chicxulub in the Yucatan sea off Mexico). Evidence is based on levels of iridium (a common element of many asteroids) that are high in K-T sediments. The resulting blast would have created climatic havoc (such as hurricanes) and huge amounts of dust and vapor would have entered the upper atmosphere. This would have been compounded by global fires (a lot of soot is also found in the K-T deposits). All of these combined events would have cut-off sunlight for many months, resulting in a darkness that prevented photosynthesis and is thought to have caused this massive extinction. The real question is how the crocodiles and alligators survive when their cousins expired?











    By Anonymous Rich, at Friday, March 17, 2006 10:01:00 pm  

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