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by zerogreen on August 14th, 2003

zerogreen

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If all life started from single celled organisms, why were the dinosaurs so big in comparison to today's animals?

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  • by DOSJockey382 on September 22nd, 2003

    DOSJockey382

    Current theory, as I understand it, holds that life started in the oceans as single celled organisms. A fluidic medium is required for these single celled organisms to have any control over their intereaction with the environment around them. A fluid, specifically water, is dense enough to allow the self-propulsion of the single celled creature so that it can find and ingest food sources. Most gas media, such as air, are significantly less dense, and any means of locomotion would be capricious and dictated with the currents of the medium.

    The original multicelled creatures were little more than large colonies of single celled organisms. These colonies can take up vast amounts of space. As the varying portions of these colonies became more and more interdependent, multicelled organisms eventually took on the organizational patterns that we are familiar with in today's multicellular creatures. Water environments nullify much of the effects of gravity, allowing many of these organisms to retain their great size. Even today, the largest living creatures on the planet are whales.

    As creatures moved from water to land, they retained much of their great size. First these creatures had to adapt the proper physical structures to become land dwellers. Fins and flippers became legs and feet. Gills became lungs. Once these creatures had adapted to being able to support themselves on land for the long term, gravity would then have her say. Regardless of how successful some of these large creatures were, smaller forms are more efficient in higher gravity environments. The larger the creature, the more energy needed to maintain its ability to survive. For land-based creatures, there is nothing supporting them but their own bone, sinew, and muscle. At least a whale has water to help support its body weight. Not only that, large animals are easier targets for predators, no matter how ferocious they are. A single large animal is rarely a match for a pack of smaller ones. Smaller prey animals can hide much easier than larger prey aniamls. Also, Larger animals will deplete a given food source within an area more quickly than a smaller animal. Smaller animals usually breed more quickly, so they are able to take less food individually but take more food collectively.

    The size of creatures continued to decrease until they were more compatible with the environment they lived in, hence today's smaller size creatures relative to the large size of the dinosaurs.

    Comments

    • Makes sense!

      JP1967

      by JP1967 on December 25th, 2003

    • Current theory states that whales moved from land to the water...

      Baneblessed

      by Baneblessed on November 15th, 2004

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