Evolution ‘favours bigger sea creatures’

Feb 23, 2015

By Jonathan Webb

The animals in the ocean have been getting bigger, on average, since the Cambrian period – and not by chance.

That is the finding of a huge new survey of marine life past and present, published in the journal Science.

It describes a pattern of increasing body size that cannot be explained by random “drift”, but suggests bigger animals generally fare better at sea.

In the past 542 million years, the average size of a marine animal has gone up by a factor of 150.

It appears that the explosion of different life forms near the start of that time window eventually skewed decisively towards bulkier animals.

Measured by volume, today’s tiniest sea critter is less than 10 times smaller than its Cambrian counterpart; both are minuscule, sub-millimetre crustaceans. But at the other end of the scale, the mighty blue whale is more than 100,000 times the size of the largest animal the Cambrian could offer: a trilobite less than half a metre long.


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8 comments on “Evolution ‘favours bigger sea creatures’

  • Oh boy! A huge new survey! In ten years someone will have a bigger, newer study saying the exact opposite. Pound for pound there are more smaller creatures in the oceans. Explain that.



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  • A3Kr0n Feb 23, 2015 at 6:05 pm

    Oh boy! A huge new survey! In ten years someone will have a bigger, newer study saying the exact opposite.

    Actually the OP says that some creatures are many times smaller.

    @OP- Measured by volume, today’s tiniest sea critter is less than 10 times smaller than its Cambrian counterpart; both are minuscule, sub-millimetre crustaceans. But at the other end of the scale, the mighty blue whale is more than 100,000 times the size of the largest animal the Cambrian could offer: a trilobite less than half a metre long.



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  • Oh, there is explanation in source article; it says:

    You can see in the data, there is this trend to increasing size – but
    a real kick comes when you have these air-breathers re-entering the
    water. … Then you have a sort of a step change in size. Breathing
    air delivers extra oxygen to an animal’s tissues, he explained,
    allowing them to sustain bigger bodies beneath the waves. … They
    actually have a fairly small impact on the mean size.

    I simply adore such news about animals. At first in my layman’s brain,I thought that they could get bigger because the predators (ones existed) extinct. After that, they could move faster, and for that they needed strenght and to be bigger. hahaha



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  • Modesti Feb 24, 2015 at 3:08 am

    Breathing air delivers extra oxygen to an animal’s tissues, he explained,
    allowing them to sustain bigger bodies beneath the waves.

    As warm-blooded populations expand towards the poles, heat retention because of in improved volume to surface area ratio, becomes a factor.

    Reptiles, such as Salty Crocs can only live in warm tropical waters.



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  • 7
    NearlyNakedApe says:

    On the other hand, bigger creatures have to spend more energy to move around and therefore need more food to ensure their sustenance and the sustenance of their offspring. Isn’t this idea about size being an evolutionary advantage only valid in an environment where the food supply is plentiful?

    In an environment where the food supply is dwindling (eg. a dying ocean), wouldn’t the reverse be true? Wouldn’t evolutionary pressures favor a decrease in size? Look at what happened during the Cretaceous extinction, the big dinosaurs went extinct for lack of food while the small mammals not only survived but thrived.



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