
Evolution 'favours bigger sea creatures' - Libertatea
http://m.bbc.com/news/science-environment-31533744
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tokenadult
Reading down through the article kindly submitted here after first reading the
previous comments, I see, "Certain key events, also highlighted by the study's
authors, deliver an extra boost. Most obviously, at the stages when land
animals like reptiles and, later, mammals returned to the water, the size
graph lurched upward.

"It was the return of mammals, after all, that eventually produced the modern
giants of the sea: whales.

"'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,' Dr
Berenbrink told the BBC.

"'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."

Oxygen-delivery systems indeed have to be crucial for animal life on land or
in the sea. Fish and their gills simply can't bring in as much oxygen for an
energetic large-mass lifestyle as whales and their lungs can. It would be
interesting to find out how much whale blood deoxygenates as it flows through
the tissues of the largest whales. The duration of movement on one breath for
whales is already quite impressive compared to what most land mammals can
achieve, so whales probably have some good adaptations for efficient use of
oxygen from each breath.

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jessaustin
I have a dream, that someday a science editor will read an article in which
the word "average" appears and then suggest that the word "median" should also
appear.

TFA: " _Today 's tiniest sea critter is less than 10 times smaller than its
Cambrian counterpart, measured in terms of volume; both are minuscule
crustaceans._"

Presumably we're talking about _Stygotantulus stocki_ , which is 94 µm long.
That's already smaller than a lot of bacteria, so I'm not sure how much more
it could possibly shrink? There is an effective lower bound here.

TFA: " _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: another
crustacean with a clam-like, hinged shell._ "

Leaving aside the apples-to-rutabagas comparison of clams and mammals, is
there any physical reason why whales are the largest animal we could imagine?
They're big, but so is the ocean. There is no effective upper bound in sight.

Average is not a meaningful statistic in this case.

~~~
mrec
Also, does "less than 10 times smaller" mean e.g. 9 times smaller, or e.g. 11
times smaller? From context I'd guess that TFA intended the latter, but it's
horrible writing.

~~~
remarkEon
I think it means 9 times...I think. Sometimes reading statistical comparisons
in the news is just insufferable.

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ianbicking
Reminds me about this Memory Palace (a short podcast) about lobsters:
[http://thememorypalace.us/2010/08/episode-33-lost-
lobsters/](http://thememorypalace.us/2010/08/episode-33-lost-lobsters/) – not
very long ago they used to be gigantic compared to now. Evolution of the
moment often favors animals that aren't as easy prey for humans.

Somewhere else I read, I think a comment in AskScience about how insects used
to be gigantic, an evolutionary biologist noted that over time species evolve
to become larger. I would infer that given a set of ecological constraints,
bigger is usually better for intraspecies competition (having already settled
upon a successful niche for the species in general). But then things change,
the species itself must compete anew as the ecology changes, and there can be
resets, reverting back to smaller more efficient forms.

Another thing alluded to in the article is that there's some complexity to
simply maintaining larger forms. E.g., breathing air is more efficient if you
have to bring in large amounts of oxygen. The crustacean line simply hasn't
explored these areas. So even if there were always advantages to larger forms,
not everything can just get bigger. But it always leaves the question, what
about dinosaurs? So odd that the only true remnant seems to be birds that went
down such a different path.

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msane
I like the insight that air breathing animals have stronger energy input
systems than those with gills. Respiration in mammals is an energy system
evolved for land, where the constraints involve 5 degrees of freedom and
normal g. The ocean has 6 degrees of freedom and reduced g. So in the case
that an organism's niche can be improved by evolving to be larger and they
have an energy system which can support more flesh, doing so is easier in the
ocean than on land. It's true for all ocean animals but it's especially true
for mammals.

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disputin
"larger species likely took advantage of being able to move faster, burrow
better in sediment, or eat larger prey" \-- larger species burrow?

~~~
ufo
The study was not just about whales. It also covered lots of kinds of
invertebrates.

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JoeAltmaier
I'm suspicious - maybe larger animals didn't fare so well as fossils? Or maybe
atmospheric oxygen has increased or something, that directly drove evoloution.
The claim that larger is better is groundless without some engine to drive
that claim.

~~~
Retric
More likely you need more complex structures overall to support a larger size
which take time to evolve. Consider air breathing whales are significantly
larger than any fish in part because they can use Air for oxygen, but also
because their bones are stronger. But, also such animals have more body mass
and take longer to grow so they need significantly better defenses vs cancer.

