Hot-blooded crocodiles?

| 49 Comments
croc heart

Crocodiles are beasts with an odd mix of features: they are ectothermic (meaning that they derive their body heat from their environment) reptiles, like lizards and snakes, but unlike those smaller critters, they have a fairly sophisticated, high performance cardiovascular system: they have a true four-chambered heart, just like us mammals and birds, and they also have a diaphragmaticus, a muscle analogous to our diaphragm that is used to inflate the lungs. At the same time, their hearts are relatively small—heart mass is roughly 0.15% of body mass, compared to 0.4%-0.7% of body mass for mammals—and generates relatively low systemic blood pressure.

It's weird. It's like they have this fancy, sophisticated engine in low-tech chassis, that the animal never revs up to its full potential. How did it get in there, and why do crocodiles have such fancy hearts?

The answer may be that they inherited it from more active, endothermic ancestors.

Continue reading "Hot-blooded crocodiles?" (on Pharyngula)

49 Comments

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Jan Wrote:

Many of us see this as further evidence of intelligent design

Interesting.…can you provide details on the design method, and details of how this design was implemented? Oh yes.…any details on the designer would be helpful as well. Finally.…how would that be a better explanation than the hypothesis that crocodiles simply had endothermic ancestors?

Conversely, it would be nice to have some doable test capable of demonstrating that crocodiles did NOT have endothermic ancestors, if in fact they did not. Otherwise, we’re just comparing stories.

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Many of us see this as further evidence of intelligent design rather than a “weird, … sophisticated engine in low-tech chassis.”

Further evidence? This is evidence for ID for you people, this is all it takes? I can’t explain it so it becomes ‘evidence’.

How silly,no wonder it lacks support from 99.9% of scientists.

Perhaps our cognitive predispostition toward teleological constructions is a byproduct of a more general adaptation.

Flint Wrote:

Conversely, it would be nice to have some doable test capable of demonstrating that crocodiles did NOT have endothermic ancestors, if in fact they did not. Otherwise, we’re just comparing stories.

Except for the fact that there is no evidence to support the ID story. At least the endothermic hypothesis has some supporting evidence; in that the modern crocs have plumbing that is suitable to endothermic metabolism even though it is no longer used as such.

I do not know if your proposed test would be possible, attempting to demonstrate the positive [that they did have endothermic ancestors] and failing to do so would accomplish the same result, but from a different direction.

I know PZ did not intend to invoke teleology, and were he to frame the question more carefully, he could dispense with the “why,” but it is somewhat interesting (at least to me) that naturalists frequently use such language.

Took me a few readings to parse this, and I can only guess that I have it right.

I read PZ Myers’ question to say “How did it happen that crocodiles have such fancy hearts?” In other words, what could be the history that has resulted in the current physiology?

I read Finley’s interpretation of this question as “what could be the intended purpose for such fancy hearts?” I admit I would never have seen the question that way if Finley hadn’t pointed this out.

Michael Finley Wrote:

There seems to be something irresistable about explanations in terms of final cause

While I agree that there are frequent references that smack of teleology (we often hear scientists refer to “design” of certain organs, appendages or functions, e.g.)I don’t see anything like that in the quote you refer to. An observation regarding the crocodile’s cardiac apparatus in its present state bears no suggestion that its present state is one towards which anything was purposefully directed.

Ken Shackleton:

I do not know if your proposed test would be possible, attempting to demonstrate the positive [that they did have endothermic ancestors] and failing to do so would accomplish the same result, but from a different direction.

I can’t agree. We’ve been around this block a few times now, where creationists make the claim that falsifiability is not required, all that’s required is the failure to find any exceptions. And since we can’t find exceptions to the claim something was created, that’s good enough to ‘prove’ creation.

Failure to find evidence for something is NOT the same as finding evidence against. If in fact we can’t determine even in principle that crocodiles’ ancestors were exo or endothermic, we are telling stories. If we consider the plumbing of the crocodile strong enough evidence of endothermic ancestry, then let’s just say so. If not, let’s say what we’d need to find to support this hypothesis more fully.

Flint Wrote:

Failure to find evidence for something is NOT the same as finding evidence against. If in fact we can’t determine even in principle that crocodiles’ ancestors were exo or endothermic, we are telling stories. If we consider the plumbing of the crocodile strong enough evidence of endothermic ancestry, then let’s just say so. If not, let’s say what we’d need to find to support this hypothesis more fully.

I agree, finding positive evidence [for or against the position] is far better than saying that nothing has been found against, therefore it is true [which, upon reflection, would not be a valid conclusion]. I am just not sure how it could be done.

I do not think that there is enough evidence to make any conclusions beyond saying that endothermic ancestry is possible and should be investigated further. It is a fascinating possibility though.

Any teleology in my comment is entirely in the mind of the reader. The word “why” is a useful part of the English language with a wide range of connotations; when I see it, I see no implication of purpose.

Re “finding positive evidence [for or against the position] is far better than saying that nothing has been found against, therefore it is true [which, upon reflection, would not be a valid conclusion]”

Unless that “nothing against” is in spite of there being lots of places where something “against” would be expected to be found if the hypothesis is wrong. Or would that be counted as positive evidence in that case?

Henry

Any teleology in my comment is entirely in the mind of the reader.

Yes, of course. What’s fascinating is which readers see teleology where it doesn’t exist and isn’t intended. These same readers see Intention wherever they look. So obvious they can’t miss it.

Though, to be fair, Finley does have a point that goes a little further than the fact that “why” can mean “how does it happen that…” as well as “for what purpose…”. Given a biological structure, the genes for which show obvious conservation, “dogmatic darwinists” will usually at least tentatively assume that there is some selective pressure exerted on it - that it’s performing some important function. If you ask “why are histone genes so highly conserved?” for instance, in a way you’re asking “what critical function is met by these genes?” I think “evolutionists” often use “teleological shorthand” to convey exactly that.

As a biologist who works extensively with crocoilians I may suggest that the concept of an endothermic crocodile is not such a leap of logic at all.

1.First crocodilians genetically are closer to turtles and birds than snakes/lizards. They share much with birds, who shared much with dinosaurs. It is not a thought without merit to say crocodilians evolved an endothermic metabolism but that later it was selected against. Why?

2. Whereas the ancestors of crocodilians were primarily terrestrial predators modern crocodlians are, of course, waters edge predators. Endothermic metabolism is expensive to maintain whereas ectothermic metabolism would be a significant survival skill for an animal who can enjoy the protection of thermoregulation between aquatic and terrestrial environments.

So it is possible that a terrestrial crocodilian found endothermy profitable while after returning to an aquatic lifestyle found ectothermy an advantage. Natural selection simply modified the animal to adapt to a changing environment and new environmental niche for which they are perfect.

Flint Wrote:

What’s fascinating is which readers see teleology where it doesn’t exist and isn’t intended. These same readers see Intention wherever they look. So obvious they can’t miss it.

This falls into the theme of being too “smart” for our own good. Humans can’t help but be obsessed with patterns, and it causes all sorts of mischief with our beliefs.

Just as we are predisposed to “finding” faces in the shifting forms of clouds, so are we predisposed to spotting “teleology” everywhere we cast our gaze, or our ears for that matter, linguistic conventions notwithstanding.

again, since teleology has raised its “ugly” head, i give you:

http://plato.stanford.edu/entries/t[…]ogy-biology/

just to help inform those who wonder what the argument against using teleological arguments in biology is about.

cheers

There is a single light of science, and to brighten it anywhere is to brighten it everywhere. –Isaac Asimov

Would “dognatic darwinists” argue that the reason some gene is highly conserved is because lineages that failed to conserve it so highly aren’t around anymore? If evolution is a giant game of trial and error and some genes don’t change a single molecule in hundreds of millions of years, perhaps we can presume that any changes were exactly the sort of error natural selection corrects.

Russell: yes, it is often used to imply selection as a causative agent. I’m mostly innocent of that reflex, though, because my usual bias is that it is a developmental reason.

Flint:

perhaps we can presume that any changes were exactly the sort of error natural selection corrects.

Yes. But in this discussion where we’re having to watch our language very carefully, I wouldn’t say natural selection “corrects” errors - it punishes them severely.

Once again an attempt is made to discredit those who reach a different conclusion than the majority here. Perhaps what you see as “silly” is actually something that you are unable to comprehend. You draw your conclusions on the basis of your scientific findings, non of which are conclusive. Obviously you are making a leap of ‘faith’, but it is what you believe. Let me ask you a question. It is likely that each of you have someone in your life that you love. Could you prove scientifically that you love the person? If not, does that mean that your love does not exist? Certainly you could give evidence of your love and others could conclude that you love, but to prove conclusively would not be possible. Would that mean that you are “silly” to say that you love someone? Life as we experience it here on Earth does not lend itself to being explained completely by scientific discovery. Certainly we can learn much about life and life processes, but to determine origin and purpose are outside of the realm of science. Scientist would do well to state this at the onset rather than be dogmatic and attempt to rule out any discussion or thought of a Designer or Creator who designs and creates with a purpose.

Flint:

I would say you are making an invalid comparison:

Would “dognatic darwinists” argue that the reason some gene is highly conserved is because lineages that failed to conserve it so highly aren’t around anymore?

A gene is only useful so long as it provides survivabilty to the organism. If the climate shifts, population shifts, etc a once advantagous genetic makeup could become a disadvantage. As in the crocodile above, if endothermy was a benefit while the predator was terrestrial but a negative when the climate changed it would then be selected against. It’s not an upward climb.

If evolution is a giant game of trial and error and some genes don’t change a single molecule in hundreds of millions of years,

It’s not really trial and error, your always building on what is there. Its about survival. If a gene provides a stable living, it will remain relatively constant, if it doesn’t the organism will be modified or eliminated. No real chance involved.

perhaps we can presume that any changes were exactly the sort of error natural selection corrects.

Maybe so.

“Could you prove scientifically that you love the person?”

hmm, let’s give it the old college effort shall we?

http://www.economist.com/printediti[…]y_ID=2424049

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Jan Wrote:

Certainly we can learn much about life and life processes, but to determine origin and purpose are outside of the realm of science.

Is there any reason that you assert this other than that you want your religion’s account of creation to be correct? Disregarding any religious reasons for making your claim, do you have any reason to assert it? What makes the origin of life so different from other issues that science investigates?

Bioherper Wrote:

First crocodilians genetically are closer to turtles and birds than snakes/lizards.

I never would’ve thought of turtles as being close to birds, but I don’t really know anything about the evolution of turtles. But I’m curious: what’s the closest living relative of the turtles, and what was their most recent common ancestor like?

DC:

As I picture it, evolvability itself evolved. There’s probably some happy medium of evolutionary rate at least potentially: Too rigid, and (as you point out) normal environmental change may leave fixed organisms behind. But too loosey-goosey, and beneficial traits would be too difficult to preserve either. I speculate that when life first started, before gene conservation and appropriate “proofreading” during cell reproduction and other such mechanisms, both excessive rigidity and excessive variation were more common than today. We could say a potential to evolve that was easily rapid enough to accommodate most (certainly not all) rates of environmental change, yet not too rapid, is what was selected for (or as Russell prefers, not selected against).

Uber:

Obviously you are making a leap of ‘faith’, but it is what you believe.

…No faith necessary with evidence.

I think you may have misunderstood Jan’s point. At some point, faith is always required, even if that point is not reached until you must say that evidence matters (a statement of faith). Scientific explanations are forever incomplete, but some of us find them “good enough” because the predictions they imply are accurate so very often.

Jan simply hasn’t thought through the implications of what s/he says, by lumping origins (in principle capable of being determined by science) together with purpose (in principle NOT capable of such determination). However, science can never produce any explanations with absolute certainty, so accepting scientific explanations requires a bit of faith in that respect. However, religion (which DOES guarantee absolute certainty, at the expense of correctness) requires faith of a different sort.

Ahhhh but Flint

One is a rational faith at worst, while the other is completely irrational at best.

“There’s probably some happy medium of evolutionary rate at least potentially”

how would you arrive at this “value”, and how would it have any meaning?

“normal environmental change” is also a meaningless derivation. no such thing. selective pressures are EXTREMELY relative to the time and place (also remember they include a lot more than changes strictly due to environment as well).

the problem is that the relative level of variability in a given geographic region could (and does) vary widely over time; and periodic catastrophic events probably also play a large role, both on a local scale in a short geologic time frame (like hurricanes), and on a global scale wrt to large-scale catastrophic events (like ice ages).

moreover, as i mentioned, selective pressures don’t just include physical processes of environment. often the most important selective pressures are biological.

cheers

Re “evolution of turtles. “

The webpage Amniota ( Mammals, reptiles (turtles, lizards, Sphenodon, crocodiles, birds) and their extinct relatives) shows turtles as branching off first from the Diapsida (the group containing lizards, crocodiles, and birds), but it shows a question mark indicating uncertainty as to the placement of the Testudine (turtle, tortoise, terrapin) clade.

Henry

Uber:

I agree. Absolute knowledge is a snare and a delusion; at some point we must play the odds as best we can assess them. But I like to give the benefit of the doubt, because it helps clarify that people do NOT have certainty, never can and never will. Most people WANT certainty, and most of them seem perfectly capable of pretending they have it. They call this pretense ‘faith’. But it’s certainly a different species of faith than you have.

Sir-Toejam:

I don’t think I communicated with you very well. Let’s say I speculate that most types of environmental change are fairly gradual (climate change, elevation change, etc.) and life forms have been able to track this rate of change without much difficulty. Mass extinctions, however, imply that there are at least some environmental changes too rapid for biological tracking to follow.

I think I could in principle arrive at a range of values for “ideal” evolutionary motion, at least as a computer model. No change would spell universal extinction sooner or later. Too much change would leave a good many niches for more conservative life forms to claim and defend. At least in my model. So I also speculate that life “experimented” with these various rates, especially early on, and those at the ends of the curve lost out. I’m not the only one to suspect that the ability to evolve has itself been the target of natural selection.

I don’t disagree with anything you say.

“Could you prove scientifically that you love the person?”

Yes. I watched The Notebook with my wife. That proves that I love her.

A more thoughtful gloss on my “proof” would point out that you are relying on a division between inner and outer criteria that is a relic of modern philosophy of mind. In actuality, thoughts, beliefs and desires (believe it or not, there are some who would deny the existence of these; happily, I’m not among them) are intractibly interwoven with behaviors and practices. These “outward” behaviors bear a necessary relationship to their “inner” counterparts; in fact, the division is illicit, and therefore, certain behaviors and practices are, quite simply, instances of love (see Wittgenstein’s Remarks on the Philosophy of Psychology).

I’m going to take some more time to think about it, but i believe you are a bit off here.

“Mass extinctions, however, imply that there are at least some environmental changes too rapid for biological tracking to follow.”

indeed, it would also imply that evolutionary bottlenecks might play a larger role in the “evolution of evolution” than any fairly gradual effect.

I don’t see how the outcome of a bottleneck would “average” meaningfully with the outcome of gradual change.

do you see what i am getting at?

you might be able to create a mathematical construct that would derive some sort of “average” but how meaningful would that actually be?

“Too much change would leave a good many niches for more conservative life forms to claim and defend. At least in my model. So I also speculate that life “experimented” with these various rates, especially early on, and those at the ends of the curve lost out.”

no, in fact what we see is the exact opposite. Have you ever studied r vs. K selection?

the whole argument wouldn’t even exist if there was some “average” evolutionary strategy and rate.

Can you see how different rates would be advantageous at different times from your own argument? It predicts divergence, not convergence.

Jan:

Are you the same Jan from whom I am still waiting for answers to questions I posted months ago? Your use of the singular “scientist” in the later post suggests so. If not, or if you forgot me, I happen to believe in design, and accept evolution.

Note that the article you linked is copyrighted 2003, and quotes Denton’s 1986 work to support its promotion of incredulity toward common descent. Denton later accepted common descent, and even wrote a well-known book about it, “Nature’s Destiny” (1998), in which he corrects his earlier misconceptions. So the article is at best irresponsible journalism, and at worst, willful misrepresentation. Sadly, nearly 100% of pseudoscientific anti-evolution articles published after 1998 make the same glaring omission. In case you forgot, God doesn’t like it when people bear false witness.

Denton’s acceptance of common descent does not make it necessarily true, of course, but multiple lines of independence evidence do. The authors of your article misrepresent that too. And they reference Patterson liberally. I haven’t checked whether they quoted him out of context, but that too is standard practice for pseudoscientific anti-evolutionists. So it behooves you to be as skeptical of such articles as you are incredulous of evolution (or pretend to be).

Jan Wrote:

Once again an attempt is made to discredit those who reach a different conclusion than the majority here. Perhaps what you see as “silly” is actually something that you are unable to comprehend.

Comprehend? Most certainly.…but if it is not supported by evidence, then it does not merit scientific discussion.

Jan Wrote:

You draw your conclusions on the basis of your scientific findings, non of which are conclusive. Obviously you are making a leap of ‘faith’, but it is what you believe.

If you define “conclusive” as absolute.…then nothing in life or nature is conclusive in any absolute sense. If by “conclusive” you mean that sufficient evidence exists to reasonably accept the hypothesis.…then many scientific findings are conclusive.

It is the belief in that for which there is no evidence that requires faith.

Jan Wrote:

Let me ask you a question. It is likely that each of you have someone in your life that you love. Could you prove scientifically that you love the person? If not, does that mean that your love does not exist?

I love my wife and kids, but I may not be able to “prove” it. However, it would only mean that I cannot prove it, it does not mean that my love does not exist. In the same vein, science cannot prove or disprove the existence of a Creator because such proof requires evidence that does not exist. This does not mean that the Creator does not exist, it only means that such existence cannot be supported by evidence.….much the same as my love for my wife.

Jan Wrote:

Certainly you could give evidence of your love and others could conclude that you love, but to prove conclusively would not be possible. Would that mean that you are “silly” to say that you love someone? Life as we experience it here on Earth does not lend itself to being explained completely by scientific discovery.

Your definition of conclusive seems to be an absolute.…that is your error. Science has never claimed to be able to explain anything “completely”.

Jan Wrote:

Certainly we can learn much about life and life processes, but to determine origin and purpose are outside of the realm of science.

Incorrect assumption on the origin, correct assumption on purpose.

Jan Wrote:

Scientist would do well to state this at the onset rather than be dogmatic and attempt to rule out any discussion or thought of a Designer or Creator who designs and creates with a purpose.

If there is ever any evidence of a Designer or Creator, then it would merit scientific discussion. Until that day, it will be outside the realm of science and left to philosophers.

(On Sir_Toejam’s comment about r vs K selection in #25790 above)

I was under the impression that r vs K selection is about reproductive rates, not mutation rates. Basically a tradeoff between producing as many offspring as possible vs. producing a few offspring with low mortality rates.

While “optimal” mutation rates could be different in “r” situations than in “K” situations this would not appear to be immediately obvious.

See the galloping crocs here!

http://www.flmnh.ufl.edu/natsci/her[…]rittoncrocs/

Read somewhere that leatherback turtles are endothermic - markedly so. Perhaps a diet of jellies is just the thing. Could one tell they’re endothermic (if indeed they are) from dissecting a dead one?

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On turtles: According to Zug, (Herpetology, 1993) turtle fossils extend back to the late Triassic (Proganochelys). But he doesn’t suggest a “common” ancestor.

There were two Paleozoic anapsid lineages, Testudines and Captorhinidae, but molecular and DNA studies may end up with turtles as archosauromorphs. Interesting times.

Turtle Origins

Textbooks portray turtles as the most primitive group of egg-laying animals (amniotes) in existence and extol their virtues as model organisms for primitive amniote organization and physiology. In their report published on page 998 of this issue, Hedges and Poling (1) present an exhaustive analysis of turtle relationships on the basis of DNA data. Their results, which support other recent analyses of protein (2) and DNA (3, 4) sequences, indicate that instead of being related to the anapsid root of the reptile evolutionary tree, turtles nest in the tree crown, within Diapsida. These molecular data thus are partially congruent with morphological characters that also support diapsid (5), rather than anapsid (6), turtle relationships. However, the molecular data conflict with paleontological data as to where exactly turtles fit within diapsids. The DNA data also support a highly controversial relationship of the Tuatara, and it will be a challenge not only to paleontologists, as suggested by Hedges and Poling, but also to molecular systematists to resolve these conflicts. … Morphological data (5, 12) place the turtles as sister-group of the Sauropterygia, both nested at the base of the lepidosauromorph lineage. This contrasts with all available molecular data, which put turtles on the archosauromorph branch. Although the placement of turtles within Diapsida is the most parsimonious solution on the basis of all data at hand, the statistical support for both lepidosauromorph and archosauromorph affinities of turtles, on the basis of anatomical and molecular data, respectively, may be relatively weak in some cases. This reflects a high degree of independent evolution of morphological similarity (convergence) within anapsid and diapsid reptiles on the one hand, and the impact of a long separate evolution of the turtle branch on molecular characters on the other. However, an as yet unpublished morphological data set (13) places the Sauropterygia at the base of the archosauromorph lineage. The effect of inclusion of turtles into this data set has not yet been explored, but if Sauropterygia exert the same pull as they previously did (5, 11), turtles might end up as archosauromorphs on the basis of morphological characters also.

jan Wrote:

Could you prove scientifically that you love the person?

I would first need to establish a definition of what constitutes ‘love’. Then, if that definition is falsifiable, then it is possible to disprove it. That is the basic scientific method. However, it is quite possible to construct a system which is not falsifiable. This is, for instance, what homeopaths have done to deflect scientific criticism. In which case, it is outside the realm of science to judge its veracity. It is probably quite possible to create a model of ‘love’ which is equally unfalsifiable.

jan Wrote:

Scientist would do well to state this at the onset rather than be dogmatic and attempt to rule out any discussion or thought of a Designer or Creator who designs and creates with a purpose.

The problem is that if something is outside the realm of science, it would require a new framework in order to determine its veracity. Unfortunately, none has been created that is capable of judging whether or not ‘God’ exists.

Thank you, wildlifer.

Jan -

Any features an organism has you can say was intended by an intelligent designer that had the ability to obtain what we observe. This works, because you bury the observations you seek to explain in there existing a completely hypothetical designer with no independent evidence having the goal and ability to create your observations. This can be done with literally anything, from volcanoes to vertebrate eyes, and is completely useless. It explains nothing. The only constraints on the potential intentions and abilities of an assumed hypothetical designer are artificial ones you might put on it - such as religious doctrine.

For further discussion of this concept, see Elliot Sober’s paper:

Intelligent Design and Probablity Reasoning.

http://philosophy.wisc.edu/sober/ID[…]d.PDF#search=’Intelligent%20Design%20and%20probability%20reasoning’

Sir Toejam,

I’m still not sure if we are communicating. I see what you are driving at, I think, but it wasn’t what I was trying to say. Consider absurd extremes: A lineage unable to evolve at all, and another, uh, perhaps “lineage” is the wrong term, where offspring differ from parent so completely that their ability to mate even with siblings is unlikely. I suggest that neither of these extremes would be around for more than a few generations. Instead, what I would expect to be selected for is the ability to evolve reasonably quickly, “reasonably” being considered as capable of adapting to periods of relatively fast change (excluding the bottlenecks).

Let me try a different tack. We see hox genes conserved to a remarkable degree (as an example). Surely (unless you are a closet creationist) these genes in all their complexity didn’t appear POOF all at once and nothing first. They must themselves be the product of selection from a broader range of precursors, most of which were NOT conserved. But anyway, back to the crocodiles…

“Let me try a different tack. We see hox genes conserved to a remarkable degree (as an example). Surely (unless you are a closet creationist) these genes in all their complexity didn’t appear POOF all at once and nothing first. They must themselves be the product of selection from a broader range of precursors, most of which were NOT conserved. But anyway, back to the crocodiles … “

okeedokee. assuming crossed wires… wiping the slate then. let’s take this step by step.

so you are arguing that the conservation of specific gene sequences is related to a previous state where non conservation was far more common, is this correct?

er wait. you have a point. let’s take this offline and get back to the crocs. email me if you would like to continue.

cheers

Perhaps our cognitive predispostition toward teleological constructions is a byproduct of a more general adaptation.

Are you saying that your cognitive predisposition away from teleological constructions is a byproduct of a less general adaption?

“So it is possible that a terrestrial crocodilian found endothermy profitable while after returning to an aquatic lifestyle found ectothermy an advantage. Natural selection simply modified the animal to adapt to a changing environment and new environmental niche for which they are perfect”. Herperbio, Are crocodiles perfect for their environmental niche? Observing their heart, far from it. It is a patchwork of fixes on former corrections. What other hotblooded animal remade itself to ectothermism when returning to water? Is echtotermism profitable for an animal with long periods of inactivity with sudden burst of intense activity?

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