Potential adaptions / features for life adapted to the level of atmospheric pressure given?

Question

Atmospheric composition:

• | 2% Trace gases | 58% Nitrogen | 26% Oxygen | 11% Argon | 3% Carbon dioxide |

Average surface temperature:

• 36 degrees Celsius

Surface gravity:

• 1.36x Earth gravity

Info regarding of altitude, pressure, and atmospheric density:

altitude    pressure    density 
(meters)    (atm)       (kg/m^3)
0           17          10 
1000        15.3        9
2000        13.8        8.1
3000        12.5        7.3
4000        11.3        6.6
5000        10.1        6
10000        6          3.6
15000        3.6        2.1
20000        2.2        1.3
30000        0.8        0.5
40000        0.3        0.2
50000        0.1        0.06

What adaptations would creatures normally have on this world based on the high pressures of the atmosphere given? Would they have looser bones? Pressurized gas within the bones? Etc? If possible, give detailed hypothetical answers, I'll be glad if examples are given in the answers for the question I'm asking

Answer 1

TL; DR:

Skip the Partial Pressures section and go directly to Adaptation; you don't need to read the sub-titles.

Partial Pressures

First, we will calculate the partial pressures of your atmosphere:

Note that I don't know the $\text{gr/mol}$ of $\text{Trace Gases}$ so I tried to make an average with your actual gases.

In addition, I don't like atmospheres so I added a column for partial pressure in kilopascals. Remember: $$\text{atm} = 101.325\text{ kPa}$$

$$ \left| \begin{array}{cc|ccc|c|cc} \text{Gas}&\text{%}&\text{gr/mol}&\text{Mols}&\text{Fractal Mol}&\text{Partial Pressure (Atm)}&\text{P.P (kPa)}\\ \text{N}_{2}&\text{58%}&28.014&2.0703&\text{62.91%}&10.69&1,083\\ \text{O}_{2}&\text{26%}&31.998&0.8125&\text{24.69%}&4.19&425\\ \text{CO}_{2}&\text{3%}&44.01&0.0681&\text{2.07}&0.35&35\\ \text{Ar}&\text{11%}&39.948&0.2753&\text{8.37%}&1.42&144\\ \text{Others}&\text{2%}&30.900&0.0647&\text{1.97%}&0.33&33\\ \text{Total}&\text{100%}&174.87&3.2911&\text{100%}&17&17,222\\ \end{array} \right| $$

• Nitrogen (N₂): 1,083 kPa (10.69 atm)
  • Nitrogen narcosis: Nitrogen narcosis is developed under pressures above 240 kPa and 354 kPa. Values above 400 kPa will produce serious nitrogen narcosis. Nitrogen narcosis is similar to drunkenness but worse. If you want to find more information in this answer I wrote about its symptoms.
• Oxygen (O2): 425 kPa (4.19 atm)
  • Oxygen Toxicity: Values of oxygen higher than 50 kPa are lethal for a terrestrial organism. That amount of oxygen burns our skin, eyes, lungs and even cells. Anyone would die in a few hours. In this, this and this answers I describe in detail their effects. The last link has a cute diagram with the effects.
• Carbon Dioxide (CO2): 35 kPa (0.35 atm)
  • Hypercapnia: Hypercapnia is the production of carbonic acid in our body due to the elevated amount of CO2 because the body wasn't able to dispatch it (due to the elevated partial pressure outside). That is lethal and will kill animals very quickly. In this and this answers you will find additional information and a graphic with the common symptoms. The last link has a table which shows the "lethality" of different values. That table shows percentages based on Earth atmospheric pressure. Talking about your world, death arrives in a matter of minutes.
• Argon (Ar): 144 kPa (1.42 atm)
  • Argon Asphyxia: Although argon is non-toxic, it is 38% denser than air and therefore considered a dangerous asphyxiant gas in closed areas. It is difficult to detect because it is colourless, odourless, and tasteless. This gas may decant into zones without wind.
  • Argon Narcosis: I don't know much about it, but it's hypothesized that argon can produce the same effects as nitrogen narcosis but only at higher pressures.

Adaptations

I have done the analysis of the atmosphere but your question wasn't about if humans could survive, so we must think now which adaptations will need your creatures.

• Faster metabolism due to the increase in oxygen.
• Faster ageing, short lifespan, a lot of offspring (due to oxidative stress and stuff).
• Bigger insects (again, oxygen).
• Smaller lungs and possibly moister eyes and skin (oxygen and a bit of nitrogen). Insect respiratory system for smaller animals.
• Maybe some tweaks to the brain to avoid narcosis.
• Maybe the ability to smell argon.
• Stronger muscles and bones to counteract gravity. Shorter creatures.
• Increased sweating and ectothermic animals for the elevated temperature.

Oxygen

Your oxygen levels are too high; that will hurt their eyes, skin and lungs.

Your species will need very small lungs because they will be able to collect a lot more oxygen with the same amount of space due the elevated oxygen pressure. I wouldn't be surprised to find "poorly evolved" lungs since efficiency isn't necessary here.

This oxygen will make metals rust faster due the increased oxidation speed. Flammable things will be even more dangerous. Oxygen has a lot of ROS, molecules that break DNA, proteins or organelles in cells (for more information see this answer). These damages accelerate ageing (also explained in the link above). Your creatures will have a very short lifespan but a lot of offspring to compensate.

Some ways to reduce this effect are the implementation of active transport (which consumes huge amounts of energy) or semipermeables membranes. Both are explained on the link for the paragraph above.

Furthermore, (also explained in that link), your insects will be HUGE. (Short-long-answer, insects don't have lungs; they breathe through the skin. More oxygen compensates for the lack of surface-volume relation, which lets them grow more). Because your vast oxygen partial pressure, I'm quite sure this technique will also be possible for smaller animals.

Finally, they may need wet skin and wetter eyes to counteract oxygen oxidation.

Nitrogen

No idea how to fight that, maybe smaller lungs will fix that. Some modification to the brain (not sure how) may reduce nitrogen narcosis. If they evolve there, they must be used to being "drunken".

Argon

Your creatures will need a way to smell argon, or they will accidentally die in an argon well because it's heavier and can get sunk in valleys or plains.

Gravity

An increase of only 36% isn't very bad. A healthy human can survive that fine. They will evolve with slightly stronger bones and muscles to counteract that. I will suggest hollow bones like birds to compensate for the additional weight. Also, creatures will have a shorter height.

Temperature Control

This is one of your lesser problems. Sweating more, having a lower metabolism and being cold-blooded animals will fix that. You can learn about thermoregulation in Wikipedia.

Basically, animals are divided into two big categories: endotherm and ectotherm. While the first ones produce their own heat to maintain their desired body temperature, the second category takes advantage of the environment's heat, using that as their body temperature.

I strongly advise to make your animals ectothermic, because they don't spend energy on warming up since the environment is enough to keep them warm, maybe even too much... (if 36 ºC is the average I don't dare to be there during summer...).

Anyway, we can still take some useful cooling traits from warm creatures (endotherms) before we get deep into the other. Endothermic creatures have a few mechanisms to avoid overheating:

• Panting: By panting with the tongue, they are able to lose temperature by increasing water evaporation in the breath. As you say in comments, birds' respiratory systems might be useful due to their fast breathing. I would add blood vessels which flow blood in the opposite flow direction to make countercurrent heat exchange.
• Flushing: Increasing the blood flow to the skin transfers the heat from the inner body to the skin, place where it can be radiated into the environment. I encourage your creatures to have a large surface-volume ratio to avoid gigantothermy (big animals produce too much heat that they can't remove). For example, the usage of huge ears like car radiators (blood vessels) is very useful.
• Sweating: If the creature is hairless or short-haired, it can cool itself by sweating water. Take note that this method consumes water and minerals from the body. Just for curiosity's sake, I'll tell you that endothermic creatures are more resistant to fungal infections due their own heath production. Sadly, you can't handle that. (Maybe the environmental heat is enough?). Also, your animals won't have brown adipose tissure because that is to produce heat, and you don't need more.

Now we must discuss ectotherms in more depth. As an advantage, ectotherms creatures eat a lot less (like 5 or 10 times less) because their slowed metabolism saves a lot of energy (lack of internal heating process); they are very economical! But they are only active during the day (due to the need to bask under warm sunlight), but your planet is quite hot so...

This requires cold-blooded animals to work with the fluctuations of ambient temperatures because they directly affect their body temperature. Ectothermic creatures are divided into even more categories based on how they "control" or "help" their temperature. Usually animals are very focused on one technique, but is possible to have trait of several, like reptiles. The main techniques are being poikilothermic and homeothermic.

The homeotherm is very known by everybody. These creatures try to always maintain the same body temperature, even if the temperature is only produced by the environment. Instead, poikilothermic creatures have between 4 and 10 enzyme systems (instead of 1 specialized but effective enzyme) in their bodies to survive and operate at different ranges of temperatures without problems. However, these enzymes are difficult to develop ^{[Quotation need.]} and make longer DNA (not sure if that is necessarily bad, but cool).

I don't know how your creatures are, but take note that poikilothermic creatures don't have sustained high-energy activities like powered flight (in large animals) or large brains. These creatures usually wait patiently for their prey rather than hunting actively, because they require between 10 to 20 times less energy than homeothermic animals (usually warm-blooded). And they usually seek shelter at noon but bask in the sun and takes advantage of gigantothermy to lose less heat, but luckily, on your planet there is plenty of heat! So I think they could have homeothermy, since there is enough heat to maintain a stable temperature.

Remember that even without a warm sunny day, some cold-blooded animals can still work. Some ectothermic animals have evolved to vibrate their muscles in order to generate a bit of heat when it's very necessary (this is usually done by insects, but I don't see it being difficult for other animals), a technique common in endothermic creature (like when you are cold and you begin to shiver).

For both cooling and heating, these creatures take advantage of heat exchange techniques (like countercurrent exchange). By using blood vessels, they can effectively move heat from outside to inside or from inside to outside for cooling and warming purposes. Also, the secretion of mucus is usually used to increase evaporation, and if the environment is very cold, they can enter into torpor (decreased activity)

Finally, there is a third category after endothermy and ectothermy: mesothermy. They are hybrids between both techniques, basically adapting for the environment. They usually have poor metabolic control in their bodies (like ectotherms), but if it is necessary they will metabolize brown fat to produce heat (like endotherms) or increase in size (gigantothermy).

So, to summarize, your animals must pant and sweat. Being hairless, they will retain less heat, and by sweating through their skin and panting (with a large tongue), they will be able to lose heat by evaporating water. Passive techniques that don't require water will be flushing hot blood to the skin to radiate heat. It will be very advisable to increase the surface-volume ratio to avoid gigantothermy, like having big ears like elephants, many blood vessels, and the ability to move at will. In this way, they will be able to radiate heat and flap to increase the airflow.

Answer 2

Pressure is a funny thing in biology

Note what i am about to say does not apply to vaccum because i am generalizing somethings.

In many ways pressure is irrelevant to physiology. What is critical is pressure difference because that is what kills. It would be possible for a human like body to survive (if created there) in the marianas trench only to explode when brought to sea level. There are plenty of fish that are great examples of this being able to exist in both places.

This obviously isnt the whole story. Those same fish have adaptations and simpler physiology to handle rapid yet gradual changes in pressure. For instance, gases acrue in their swim bladder which must then be expelled.

Now to put your question into a little more perspective:

The highest atmospheric pressure humans have survived in is ~14.7atm which is pretty close to the 17atm listed objective. This begins to show you that not a whole lot is needed for life to survive at that pressure.

Now one thing that id like to touch on is gas exchange. The key for organisms to respire in their environment is their ability to take in the abundant environmental chemistry to use in their metabolic processes. These constructs can have a lot of dependence on pressure. Gills dont function so well in air. Matter of fact we humans have a diaphram specifically to ensure a constant circulating supply of atmosphere. In higher pressures its reported that breathing requires less exertion.

So to answer your question, there MAY be no visible outward difference in adaptations at this pressure. There may be differences in respiratory organs. Its really however your alien nature decides to solve the problem of gas exchange, which there is no universal answer for and can be beyond our immagination.

https://www.quora.com/What-is-the-maximum-atmospheric-pressure-a-human-can-survive

Answer 3

If I'm assuming that your life forms are based on Earth life forms in the first instance, the biggest problem they'll face in the environment you've designed isn't the pressure; it's the mix of gases.

When designing hypothetical atmospheres for earth based life forms, the important thing to remember is that it's all about Partial Pressure. That is to say, that it's about the volume of each gas that gets absorbed, not the pressure of the overall mix. Let's look at the obvious example first, then look at the specific ratio described.

Everyone knows that you can't breathe pure O₂; it burns out your eyes, lungs, etc. and over a given period is lethal. That said, the Apollo Astronauts spent over a week on a return trip in pure O₂ without those effects. Why? Because their capsule was only pressurised to about 0.3 ATM. In effect, if you take 1 bar (sea level pressure) as the norm, then humans regularly breathe in around 0.2 ATM of O₂ with each breath, and the Apollo Astronauts weren't breathing in much more than that in their capsules. So, it wasn't a problem.

Deep sea divers on the other hand require a special mix of air to dive deeply, because once you get below around 60m, you're in 7 Bar of pressure, meaning that every breath you take of normal air at that pressure is around 1.4 ATM of O₂, which is toxic to humans.

The deepest humans can dive in SCUBA gear where their bodies are subjected to the full pressure of the ocean is around 140m, or 15 ATM of pressure. Let's assume though that we can make the leap to 17 ATM at sea level of your chosen planet; what are the gases going to do?

Well for a start, the O₂ is definitely toxic at those levels. So is the Nitrogen, but long before it becomes toxic it'll become narcotic. At the percentages you've described, Nitrogen Narcosis would set in at around 4 ATM, and at 17 ATM I'm pretty sure it becomes toxic.

CO₂ is your real worry, though. CO₂ is toxic in very small doses, and should never be considered safe above 5% at 1 ATM. But, in your atmosphere, you've got a PP of CO₂ of around 51% (17 x 3%) meaning that animals are really going to suffer in this environment.

The Argon is fine, but the trace gasses comprise a PP of around 34% (which if it was O₂ alone would be too high) meaning that if some of that is (say) fluorine, any earth based animals in that environment are dead, end of story. At these levels, trace gasses aren't really 'trace' - the amounts breathed in by a normal earth based life form are enough to cause serious damage if any of them are dangerous because their presence is now material because of the atmospheric pressure.

So, what adaptations could we see to cater for living in such an environment? Well, obviously you no longer need an efficient gas exchange model like lungs. This is because at these pressures, pretty much everything you have in the atmosphere is a problem. So, the best solution is not to take too much of it in.

As I see it, this means 3 possibilities.

The first is smaller lungs. Lungs are still a good idea because they have the potential to be more efficient if the environment changes in some way. But, lungs will have to reduce in size as a percentage of body mass because to do otherwise will kill your subject. Chest muscles will have to be stronger to work in the higher pressure, and the bronchial tubes will no doubt be shorter and wider as well, to more effectively move the higher pressures in and out of the lungs, smaller though they may be.

The second is gills. At those pressures, you're probably better off doing what fish do and just letting the pressure and density of the gas run over a gas exchange system that's semi-external. It won't be as efficient, but then you don't want it to be, especially with the high concentrations of CO₂.

Finally, there's osmosis. Insects are likely to thrive in your environment because they don't have lungs at all; they absorb O₂ through their carapaces until it saturates their body, and waste CO₂ is then expelled through the carapaces. On Earth, this limits the size insects can grow to because if they get too big, the oxygen can't reach the innermost areas of the insect's body. We believe there were periods in Earth's past where oxygen levels were much higher than now, allowing insects to grow to much larger sizes.

In your world, this is very likely to be the case because the partial pressure will allow more O₂ to be absorbed into the insect's body, allowing for deeper saturation.

Of course, oxygen isn't the only consideration in insect size; being exoskeletal means that their carapaces can only get so big before they can't support the creature (square cube law) but certainly they would have an advantage on your world regardless.

Personally, I would expect land based creatures in your world to potentially have gills as if they formed in the ocean first (as we believe life did on Earth), it's one less change evolution would have to implement for survival.