the Coconut Crab's exoskeleton is said to be the largest allowed by the atmosphere, why?

the Coconut Crab's exoskeleton is said to be the largest allowed by the atmosphere, why?

According to Wikipedia : The coconut crab, Birgus latro, is the largest land-living arthropod in the world, and is probably at the upper limit of how big terrestrial animals with exoskeletons can become in today's atmosphere

Can anyone explain what the atmosphere has to do with the size of an organism's (particularly an arthropod's) exoskeleton?

2 Answers

  • 1 decade ago
    Favorite Answer

    This is an issue of biological scaling.

    The main problem with exoskeletons (comprised of denser elements than non-exoskeleton coverings) is that the bigger they are, the heavier they become. If you blew up an insect up to the size of an elephant, it wouldn't be able to move because it's limbs are too heavy (also because there would be more exoskeleton on the insect relative to the bones in the elephant). This is a physiological constraint.

    Couple the weight problem with the fact that exoskeleton animals rely mainly on diffusion for delivering nutrients and hormones to their cells and they have an even bigger problem. Simple diffusion works fastest across larger surface areas. When you blow up the size of exoskeleton users, their volume increases much faster than their surface areas, so diffusion is relatively much less effective. As a result, oxygen uptake gets progressively worse with increased size. This is a physical constraint.

    Finally, there is a third major problem, and it has to due with the postures of organisms. Exoskeleton users have their weight-bearing appendages sticking out sideways. When you increase the load on the lever arm, it becomes much harder to lift (think of a catapult, heavier load = more force needed to launch the load). With large non-exoskeleton users, they have their weight-bearing appendages underneath the main bulk of their bodies, so they don't suffer as much when they try to move. This is a evolutionary-historical constraint.

    A side note, there were things like giant dragon flies back in the days because oxygen levels were higher than present day levels. This compensated for the V to SA ratio problem and allowed for giant exoskeleton users.

  • Anonymous
    4 years ago

    Coconut Crab Wikipedia

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