What kind of animals are my trolls?

Question

Edit: I've written an answer of my own now, and I'd appreciate it if any of you informed on the subject of evolution could review it, then inform me of its plausibility, via the comments (Of the answer).

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There are four other questions in my series of such, which I am asking to deal with problems I have encountered while working on my current worldbuilding project, which seeks to portray the biology of fantasy creatures in a viable way. The last was How can I explain the evolution of my giants?, and the previous three are linked there.

Now, I am asking about another of my fantasy beasts. The troll is featured in Scandinavian mythology as a burly, large-nosed beast that turns to dust when exposed to sunlight. Trolls are often represented in artwork as heavy-set, giant creatures, but the trolls in my project are slightly different.

My trolls are more lanky, semi-aquatic, with elongated snouts and long, goblin-like noses. Here is an illustration of a similar style of troll:

Image source: Spiderwick Chronicles Wiki

While not entirely the same, the basic anatomy is very similar. But what I can't figure out is: What kind of animal is this troll?

At first, I thought of a derived crocodilomorph with strong forearms, but I later discarded that theory because it has hair and a long, human-like nose, features which reptiles wouldn't have any reason to evolve.

My next idea was that it was amphibian. The hair could in fact be external projections of the skin - there is a frog which has such a trait. But that still doesn't explain the nose.

The only other possibility I can see is that it's a mammal. But what kind of mammal? It has quite a primate-like form, but a reptilian head and skin. However, I think this is the most likely of the three ideas I've put forward, but there are some things that need to be explained should you try to testify this statement.

So, to you, is this beast crocodilian, amphibian, primate or something else? I am open to any theory as long as it is backed-up with information and explains how the traits the troll has but its relatives don't evolve.

Edit: I've thought about this question more, and I can think of some reasons why certain traits would evolve. The hairlessness reduces drag underwater, strong forearms are good for swimming, and an elongated snout is good for snaring fish. Also, I noticed something in the picture I hadn't seen before. In the bottom left, it says:

"These long arms are perfect for reaching over a bridge and grabbing passers-by"

This instantly made me think of a crocodile's predation method, where they hide under the water and grab the snouts of zebra or wildebeest. This also supports my original crocodilomorph theory. If this inspires any ideas, or gives you clues as to why other traits would be useful for a water-to-ground ambush predator, answers would be greatly appreciated.

Answer 1

My initial reaction is that your trolls basic anatomical shape and habit suggests is evocative of three toed sloths.

They have pretty similar body shapes and are pretty good swimmers to boot.

The hair and scales combo through me at first, but I can think of biological reasons why it might exist. If this creature is a scavenger with a strong digestive system, their hands and faces could be devoid of hair and instead have leathery skin or scales. Vultures use a similar adaptation to keep organs and rotting meat from sticking to them after they feed.

The strong forearms could be used to open up corpses and drag out the pieces they want, as well as discouraging other animals, such as dogs or large scavenging birds, from stealing the corpse (hyenas, for example, use superior size to discourage cheetahs from kills).

The snout could be great for finding rotting meat, particularly animals that died near or in water. Then your trolls could drag them onto island rocks or logs and eat in relative piece. Or, if you wanted to justify the forearms more, maybe they haul the carcasses into trees to eat, like jaguars.

So yeah. My vote is a scavenging primate, genus: Bradypus, species: Charon.

Answer 2

I've thought about this more, and I think my question could be answered. So, here goes.

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The troll is a... drum roll please... crocodylomorph!

Evolutionary history of the trolls (Family Macronasidae):

11.8 million years ago, in Miocene South America, "super crocodilians" terrorized land and water. There was Charactosuchus, a giant gharial, there was Purussarus, the strongest crocodilian ever to evolve, there was Mourasuchus, a filter-feeding planktophagous crocodile.

But on the land too, there were more "super crocodilians" - namely Barinasuchus arveloi, quite possibly the largest terrestrial carnivore in the entire Cenozoic era. It was a sebesuchian - a relative of the crocodilians - and has been referred to as "an ecological vicar of the non-avian theropod dinosaurs".

Barinasuchus on the hunt. To give you a sense of scale, its prey is Xenastrapotherium , about the size of a black rhinoceros. Image source: Jagroar on Deviantart

Unlike its semi-aquatic relatives, it had long legs suitable for running. Laterally-compressed jaws crushed prey, and it was so reminiscent of predatory dinosaurs that when scientists found its teeth, on their own, they thought that the theropods had survived into the Miocene.

Enough about the facts, now for speculation.

The Miocene-Pliocene extinction nearly wiped out the sebecosuchians (The branch of Barinasuchus). However, some populations of Barinasuchus survived, but they would not remain apex predators for long.

For the first time since the Cretaceous period, South America was invaded by fauna from the north. Carnivorans like the short-faced bear and saber-tooth cats drove most of the already-declining crocodylomorphs out of their niches at the pinnacle of the food chain. The crippled populations of Barinasuchus fled from the great savannas which the carnivorans ruled, and found refuge in isolated patches of forests that were springing up as a result of the cooling climate.

During this time, some Barinuchus learnt to hunt birds, which sometimes led them up trees in search of their prey. Eventually, they would become more accustomed to life in the trees, despiting showing little adaptation for it (Besides slight dwarfing). An example of this in the real world is the tree-climbing goats of Morocco:

In Morocco, many goats climb trees, despite not being adapted for it in any way. Image source: CBS News

At first, the arboreal creatures behaved almost like arboreal lizards, gripping the trunks of trees with their bellies pressed to the bark. Eventually, evolution took its course, and in millions of years, the ex-Barinasuchus became a new family, Arborisuchidae. The long legs of the terrestrial crocodile had helped it, now becoming strong arms for climbing. The crocodilians had taken on an almost primate-like form.

But the climate was still cooling, and now the lower rainfall in the ape-crocodile's habitat was making vast swathes of forest turn to grassland. The creatures migrated northeast, where there was tropical rainforest.

The cooling climate continued to take its toll on the last of the mesoeucrocodylians, but one resistant population took up living in the swamps and marshes around river mouths in their South American home.

Some days in these great rivers, mass floods would uproot tree after tree, creating vast floating mats of logs and vegetation. This still happens today in the Amazon and many other rivers:

Gigantic "rafts" of logs can contain entire mini-ecosystems. Image source: Getty Images

Often, animals will jump aboard these massive rafts as they pass by, for protection, food or merely curiosity. Then, the log mats get washed out to sea and may sail across oceans. In this way, many alien taxa of animals colonize faraway lands - indeed, this was possibly responsible for the majority of Madagascar's entire megafauna.

The arboreal crocodylomorphs also boarded these rafts on occasion, and the currents of the Atlantic Ocean brought them to Europe. While the ape-crocodiles of South America died out due to predation, these European crocodylomorphs occupy the only large semi-aquatic niche in their ecosystems (A slot occupied by the caimans in their old home), so they flourish.

Europe's climate is much colder, so they evolved large, pointy noses to process warm air. A real-life example would be how humans evolved their noses when they moved north, whereas our brothers in the tropics have flat faces. These semi-aquatic trolls came to behave very like their cousins in the order Crocodilia, the Nile crocodiles (Crocodylus niloticus). They evolved long, filamentous integument called pycnofibres, a structure seen in pterosaurs (I picked pycnofibres because crocodylomorphs are Archosauriformes too), that looked like river weed, and long arms for grabbing prey. They were so derived from their ancestors that they became a new family, Macronasidae.

When the glaciers of the last Ice Age receded, some trolls migrated north to live in the wetlands of Scandinavia, evolving even more cold-climate adaptations like even bigger noses, more hair and stockier builds.

The Macronasids behave quite like their cousins in the genus Crocodylus, in that they conduct water-to-ground predation. When a deer, goat or sheep comes to drink at the water's edge, they explode from the water and grab the prey with their long forearms. Instead of the elongated, fish-snaring jaws of other crocodylomorphs, theirs are truncated to deliver powerful, killing bites to still their thrashing victims.

They sleep, give birth, nurse and defecate in the water, like hippopotamuses. In fact, they spend almost all of their time half-submerged, sometimes emerging to bask in the sun.

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Please let me know what you think of this theory, and I hope you like it. If you think you can best this answer, by all means do, for I am still open to other suggestions.

Answer 3

Trolls are the only remaining dinosaurs

If you are willing to turn the hair into long, thin, hair-like feathers, then make the troll a dinosaur. Some dinosaurs had feathers, so simply have these evolve to be long and thin for keeping warm as opposed to flight. The troll can be of a dinosaur lineage where feathers were never at any point intended for flight, so they are evolved over time for warmth instead. Various dinosaurs already had nasal horns, long thin claws as depicted, and probably some had webbed feet. Furthermore, if you want your trolls to be semi-aquatic in cold waters, they will need to be warm blooded, which (at least some) dinosaurs were as well.

As the only dinosaur to escape extinction 65 million years ago, it is easy to then explain any of its evolutionary traits. Having diverged so long ago, the troll is more genetically isolated than any terrestrial vertebrate other than the tuatara. Nothing else alive is very closely related to the troll, so it simply evolved to fit its cold semi-aquatic environment.

Answer 4

I'm going to go add a fourth possibility to your crocodilian, amphibian, mammalian choice list: dinosaurid.

First, the hair could be explained as pycnofibers, " hair-like filaments ... similar to, but not homologous ... with, mammalian hair". These are known mostly from pterosaurs, but could have originated in other nearby branches of the tree of life. Further, borrowing from another answer, the hair could be modified feathers of terrestrial dinos. As it is, these feathers were developed more for warmth and display than for flight, which is perfect for your troll.

Next, the aquatic nature. There are ample examples, from spinosaurus to plesiosaur that lived in or around water, had webbed feet, big lungs, were warm-blooded, and so on.

Of course, those hands look very like a velociraptor. Eerily like.

Finally, that nose. This will be a little difficult. I could fall on the now-discredited claim that sauropods had trunks. Instead, I will have to try to make this work with any of the variety of cranial projections that permeated dinosaurs, and indeed, many extant species. Granted, these projection are not noses, but many are in the right place and could mimic a nose-like structure. Perhaps it is a modified ceratopsian horn, or a reversed hadrosaurid crest. This is admittedly the weak point of my answer, but I think you can make sense of it somehow.

Answer 5

I feel like most of the in-depth information was covered (what kind of animal is it, what are its origins, etc.) have been covered, but I did notice that there weren't many explanations for the nose in the non-mammal answers. Well, my first idea is that it just had a nose, like a normal animal, but later of course realized that it's a mammalian nose no other kind of species would have. However, if it lives underwater and grabs people with its arm, perhaps it points its mouth and face at the surface of the water while hunting, so it can easily grab its victim and stuff it into its jaws. If that's it's predation method then the nose could have evolved from a crocodilian or dinosaurid nose into that long nose so it can breath while in that position.

This isn't really a full answer, but I wanted to add another possibility for that nose into the mix.

Answer 6

There are many diagnostic traits that allow us to classify animals, so let's go through them in your trolls

Face

Mammals and reptiles differ quite a bit in the overall nature of their face. Reptiles have hard faces with only a few important muscles around the jaw, whereas mammalian faces are wholly fleshy. While the lack of flesh on the face does exclude mammals, it doesn't secure a reptilian nature, as many other classes lack this feature

Nose and Ears

The nose and ears, contrary to the rest of the face, are distinctly mammalian features. This contradiction is quite easy to solve, though; many reptiles, as well as other classes, bear horns and crests on their head. It's not so implausible that such a structure could form nose/ear-like structures, especially long, impressive ones

Hair

Hair is another seemingly mammal-exclusive feature, but once more there are paths to it outside of mammals. One option is the synapsid class; hair evolved in mammalian ancestors long before facial muscles, and so it's not implausible that one such offshoot could survive and evolve into your trolls. Some dinosaurs also have hair-like feathers upon their body, which could be a candidate. Another option is the amphibians; as you say, some amphibians have hair-like gill structures, and there is no reason in principle why such gill structures couldn't grow so long underwater. A more exotic option could be strands of symbiotic algae that grow on the troll, giving the appearance of hair

Scales

Though scales are an expected trait on reptilian creatures, they are also present in synapsids, and even modern mammals like anomalures. However, scales are not found in modern amphibians, and in fact scales likely couldn't exist with the smooth moist skin required for the hair-gills. Hence, this troll can't be an amphibian. Algal hair, not being an actual part of the troll, could easily grow on scales

Limbs

The positioning of the limbs on the body seems distinctly mammalian. However, several other classes have this girdle anatomy, including some synapsids and dinosaurs. However, with synapsids, I could not find whether the mammalian face or legs evolved first, so the combination seen in trolls may not be possible. However, all dinosaurs had non-mammalian faces, so it is more plausible that these trolls may be dinosaurs. This could also be true with algal hair, with the trolls being featherless dinosaurs instead

Tail

Mammals and reptiles can often be distinguished by their tails: Mammals have narrow tails distinct from the body, where reptiles have thick, continuous tails. While there are many exceptions to this rule in the mammals, these are few and far between in reptiles. However, in synapsids, it seems like the mammalian tail predates both mammalian faces and girdles. If we assume that the girdle came before the leg, these trolls could easily sit in this transition

Conclusion

In conclusion, your trolls can be nothing other than an advanced synapsid, or cynodont. It retains the scales and facial anatomy of the first reptiles, but its postcranial skeleton has the unique features of the mammals. It also benefits from a horn like a nose, and a pair of ear frills, which give it a false air of mammalian nature