6 ms·

Evolution 'favours bigger sea creatures'

27 points by Libertatea 12y ago

disputin 12y ago
"larger species likely took advantage of being able to move faster, burrow better in sediment, or eat larger prey" -- larger species burrow?
- ufo 12y ago
  The study was not just about whales. It also covered lots of kinds of invertebrates.
- mod 12y ago
  A fish the size of your fist has a lot better chance of moving sediment than a bacteria. Large doesn't have to mean a whale. In terms of the article, we're talking about absolutely miniscule life in the Cambrian period.
- pvaldes 12y ago
  > larger species burrow? yes, gray and Humpback whales have several bottom feeding strategies that involve exposing burrowed preys and stirring up the sediment. Some dolphins do this also, is not so unusual. Some sharks and of course almost all rays do this also.
jessaustin 12y ago
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 12y ago
  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 12y ago
    I think it means 9 times...I think. Sometimes reading statistical comparisons in the news is just insufferable.
- TeMPOraL 12y ago
  The only thing that I could imagine is what also limits the size of ground animals - the ability to remove heat from the body. Volume grows with cube of radius, while surface area (and thus heat exchange area) grows only with square of radius - so the bigger you get, the more efficient your heat management mechanisms must be.
  - Lavery 12y ago
    Current large whales need enormous amounts of insulation (a big part of why they were hunted a hundred years ago) to maintain their body heat. While there is no doubt a point where heat becomes an issue for sea creatures, it's a ways away. Given the degree of overfishing we've seen in much of the world and depletion of the fish stocks, I think a more realistic upper bound would be the ability to consume enough mass. Although on an evolutionary time scale maybe fishing policy isn't as much a problem.
    - deleted 12y ago
      [deleted]
JoeAltmaier 12y ago
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 12y ago
  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.
ianbicking 12y ago
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.
tokenadult 12y ago
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.
msane 12y ago
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.

27 points by Libertatea 12y ago

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

ufo 12y ago
The study was not just about whales. It also covered lots of kinds of invertebrates.
mod 12y ago
A fish the size of your fist has a lot better chance of moving sediment than a bacteria. Large doesn't have to mean a whale. In terms of the article, we're talking about absolutely miniscule life in the Cambrian period.
pvaldes 12y ago
> larger species burrow? yes, gray and Humpback whales have several bottom feeding strategies that involve exposing burrowed preys and stirring up the sediment. Some dolphins do this also, is not so unusual. Some sharks and of course almost all rays do this also.

jessaustin 12y ago

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 12y ago
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 12y ago
  I think it means 9 times...I think. Sometimes reading statistical comparisons in the news is just insufferable.
TeMPOraL 12y ago
The only thing that I could imagine is what also limits the size of ground animals - the ability to remove heat from the body. Volume grows with cube of radius, while surface area (and thus heat exchange area) grows only with square of radius - so the bigger you get, the more efficient your heat management mechanisms must be.
- Lavery 12y ago
  Current large whales need enormous amounts of insulation (a big part of why they were hunted a hundred years ago) to maintain their body heat. While there is no doubt a point where heat becomes an issue for sea creatures, it's a ways away. Given the degree of overfishing we've seen in much of the world and depletion of the fish stocks, I think a more realistic upper bound would be the ability to consume enough mass. Although on an evolutionary time scale maybe fishing policy isn't as much a problem.
  - deleted 12y ago
    [deleted]

JoeAltmaier 12y ago

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 12y ago
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.

ianbicking 12y ago

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.

tokenadult 12y ago

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.

msane 12y ago

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.