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In a world I’m designing, one of the eldest extant intelligent species is the Trolls. These are not D&D trolls, but something else. I have a number of basic characteristics for these beings, and am wondering whether these characteristics necessarily imply anything remarkable about their physiology.

Note: Assume that everything is Earth-like unless otherwise stated.

The Basics of Trolls

Trolls are about 3m tall, and weigh about 300-400kg.

Their bodies are mostly covered in a thick, coarse hair. This hair, like that of wolverines on Earth (gulo luscus, gulo gulo) naturally inhibits ice formation.

They are viviparous and mammalian. They are also marsupials, at least in the non-technical sense that their infants are carried and suckled in a pouch.

Trolls live an average of 200 years, barring major injury.

They live principally in a large system of cold fens and moors. During the warm months, the weather is not unlike that of northern Scotland: cool and moist. During the cold months, temperatures rarely rise much above 0C except at midday, and nighttime temperatures are commonly around -15C.

Their diet consists primarily of vegetable matter, though they scrounge a certain amount of protein from insects and carrion. They do not normally hunt and eat other animals.

Trolls are immensely strong by comparison to humans, on the order of gorillas.

They are extremely durable: not only are they difficult to hurt in the first place, but they heal quite rapidly and consistently. They are not significantly prone to major disease.

The Question

Based on these characteristics, I imagine that a certain amount can be inferred at once regarding their physiology. However, I know very little about animal biology. Specifically:

  • Given these characteristics, are there other necessary or extremely likely qualities that would be remarkable? (By “remarkable,” I mean something that is not usually the case for all mammals and would probably get mentioned in a fourth-grade book on animals, but that I have not mentioned here.)

  • Are there any serious objections to animals like these trolls existing? (That is, some of these characteristics appear mutually contradictory, requiring some other as-yet unstated quality to explain—or perhaps requiring me to eliminate something.)

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  • $\begingroup$ Why do they need to be so big and strong? Rapid healing and disease resistance is definitely advantageous in the swampy environment, but short of having to lift tree trunks to get at food I don't see why the size and strength would evolve $\endgroup$ – sirlark Mar 26 '16 at 14:31
  • $\begingroup$ @sirlark There are some seriously nasty things living in the Fens with them. Most notably huge Monitor lizards, about double the size of Komodo dragons, so big they hunt mostly at twilight and on into the middle of the night--they've got enough volume to be homeothermic. The trolls defend themselves by breaking the things over their knees. (There aren't any trees -- this is properly speaking a mire.) And because it's plot-important, of course. $\endgroup$ – CAgrippa Mar 26 '16 at 14:35
  • $\begingroup$ Okay, no objections from me then $\endgroup$ – sirlark Mar 26 '16 at 14:36
  • $\begingroup$ seem light for thier height, gorrila is 165cm 150kg $\endgroup$ – Ewan Mar 26 '16 at 14:55
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    $\begingroup$ @CAgrippa Have you considered their societies, do they fight among themselves for territory or females? $\endgroup$ – Hoofing Mar 26 '16 at 21:35
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  1. Given those temperatures, and being mammals, the trolls would have a layer of blubber (like seals), or alternatively wear clothes. Assuming they have blubber, these trolls must eat a lot of fat (or sugar, to make fat).

  2. Because of their method of defending themselves by breaking things on their knees, they may have some kind of (possibly keratin-based) "bony protuberances" (like rhinoceros or dinosaurs) to shield and weaponize the parts of their anatomy used for combat.

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  • $\begingroup$ Is there any easy way to calculate how much fat and sugar they need to eat? Blubber in seals can be up to 50% of body mass, but let's say 10% (a guess!) for trolls. That's about 35kg. How many calories of sugar and fat do they have to eat to maintain this blubber? $\endgroup$ – CAgrippa Mar 26 '16 at 15:44
  • $\begingroup$ Looks like the fat content of insect larvae, though it varies a great deal, averages something like 25% of mass. There's about 9 calories per gram of fat. Supposing the trolls farm and eat a lot of really big larvae, like Witchetty grubs; figure 24g per grub, so 6g=54kcal fat per grub. How many grubs do these trolls need to eat, if that were their only diet? (it isn't, but as a rough measure). $\endgroup$ – CAgrippa Mar 26 '16 at 15:56
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    $\begingroup$ Mammals that swim in cold water need blubber because water is a much better heat conductor than air, but the only land mammal I know of that is said to have blubber is the polar bear, which lives in Arctic temperatures that get way lower than -15 C (+5 F) at night. Large sub-arctic mammals like caribou and moose don't have layers of fat thick enough to be called blubber, do they? $\endgroup$ – Hypnosifl Mar 26 '16 at 22:11
  • $\begingroup$ @Hypnosifl that could be the death of the blubber idea. If blubbery trolls were desired, perhaps they could be amphibious ( they live under bridges ... now I know why ), go naked ice fishing / swimming, or perhaps their metabolism is not as sprightly as the moose. $\endgroup$ – populacecris Mar 27 '16 at 8:05
  • $\begingroup$ @CAgrippa I think you can do the calculations. There's a conversion between calories in sugar and how much fat that would produce ( dieting sites have lots of this ). They probably enjoy the grubs and eat as many as they can ( grub roast, grub on spit, feasting ). Grub related products could be part of the troll economy ( grub oil, grub wax ). $\endgroup$ – populacecris Mar 27 '16 at 8:09
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For your first question, assuming your trolls spend any time actually in the water in their habitat they are going to have a small issue with being marsupials. Mother nature seems to have already solved this problem in the Water Opossum with a sealed, water-tight pouch.

For your second question, I think your trolls might have trouble finding enough food. As you've described them, their diet fairly closely resembles that of the gorilla, mostly plant matter with some insects. According to this source an adult male Grauer's gorilla weighs 170kg and eats 30kg of plant matter a day. That's means they eat roughly 1/6 their own body weight in plants every day. To find this much food they have to spend roughly half the day just foraging. Scaling up to your trolls, to sustain a 300-400kg body weight would require 50-70kg of plant intake per day. Keep in mind that while gorillas eat a lot of shoots and leaves much of their diet is also composed of various fruits which are more calorie dense. Those fruits may not be available in a fen. While I'm not saying its impossible for the trolls to forage that much edible plant matter in a day its certainly not going to be easy for them. There are lots of fun ways you could provide an extra food source though. Any sort of troll agriculture would work, or relaxing restrictions on hunting and eating animals to allow for fish or giant insects. Maybe there are large species of carnivorous plants that provide a lot of calories when eaten, or maybe they even eat big blocks of peat cut straight from the bog.

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  • $\begingroup$ Yummy -- peat cake! But the more I look into it, it does seem like the big problem I've got here is diet. $\endgroup$ – CAgrippa Mar 27 '16 at 6:31
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The trolls would have a low high weight to height ratio. Their BMI would be (for a 300Kg, 3m tall troll) 0.0033 as opposed to a human's of ten times that. The BMI falls with the square of the height.

In short they would be very thin and weedy creatures, They would not be strong as you suggest and would not have a insulating shape to whether the cold. They would likely need to eat frequently to overcome their fat shortages.

Can't say any more about the biology of a BMI that low but they would need to be quite different. Their hearts would need to be large to pup blood so high and would likely need large brains just to balance themselves.

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  • $\begingroup$ Can you expand a little on what such a dramatically low BMI would entail? Your answer is currently rather thin for this SE. And thanks! $\endgroup$ – CAgrippa Mar 26 '16 at 17:09
  • $\begingroup$ You just created the Prairie Chimpanzee your got everything 100 percent correct no need for further corrections or add ins just ditch the name trolls. $\endgroup$ – user5434678 Mar 26 '16 at 18:03
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    $\begingroup$ @CAgrippa I think you should make them heavier is the short answer. $\endgroup$ – Hoofing Mar 26 '16 at 21:35
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    $\begingroup$ I believe your calculation is wrong, BMI is mass in kilograms divided by the square of height in meters, in this case 300/(3^2) = 33.33... which would actually be obese for a human, not skinny. $\endgroup$ – Hypnosifl Mar 27 '16 at 4:48
  • $\begingroup$ @TheVoid what's a prairie chimpanzee? I don't turn it up on google or Wikipedia. Chimps don't get to 100kg, much less 350. So I'm not sure what you're referring to. $\endgroup$ – CAgrippa Mar 27 '16 at 5:56

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