Subnautica is an immensely popular survival game receiving high ratings everywhere. A big part of its appeal is its fascinating fauna and flora, that both feels realistic and is mesmerizing at the same time. But what if Subnautica played out in real life and planet 4546b actually existed? Would the fantastic biodiversity featured in Subnautica be realistic enough to pass as an actually evolved ecosystem? Or is it just another “Frankenstein Fauna”? Let’s dive into it!

Subnautica is a beautifully made and captivating game currently under development and released on Steam Early Access by Unknown Worlds Entertainment. The game seems to have hit the sweet spot between realism and stylization, as you quickly feel immersed in the alien world it presents to you. The colour scheme and style used are aesthetically very pleasing. But however fascinating and elegantly designed the creatures you find on your way may be, how realistic are they from an evolutionary and biological point of view?

For comparison, let’s take a look at the marine diversity on planet Earth. Even with a very superficial glance, you will quickly find yourself able to group many organisms into a few “classes” that are easily recognizable. For instance, we’ve got the bony fishes that share many things in common. There is the way their body is arranged with a head carrying a single pair of eyes, followed by a torso and a tail. They have an internal skeleton and their mouths have internal jaws that work vertically. They generally swim by undulating their body and tail in a sideways motion. Also very typical is a specific set of fins recurring in most species, and which consists of:

  1. Paired pectoral fins
  2. Paired pelvic fins
  3. Dorsal fin on the back
  4. Adipose fin halfway the tail
  5. Anal fin
  6. Caudal fin at the end of the tail

There may be some species that either lost or exaggerated some of these features, but this body plan is generally the same across the board.

General fin count of bony fish (Osteichthyes). Source: Wikipedia.

Other classes that we may recognize are: Decapod crustaceans like crabs, prawns and lobsters Cephalopods like cuttlefish, squid and octopuses So-called Starfish Anthozoans like anemones and corals And so on and so forth Classes themselves may be grouped together too, as for example sharks are very similar to bony fishes, but have some distinct differences as well, like having a skeleton made of cartilage instead of bone. And there are whales and dolphins that clearly have things in common with fishes. However, they swim in a different way by undulating their bodies vertically, have lungs instead of gills and so on. Still, it is easy to recognize that they are all vertebrates with a spinal column and more. Classes can also be subdivided into many smaller units, all the way down to the level of species.

So can we observe something similar in the submersed world of Subnautica?

The very first creature that we actually get to see in the game is the so-called “Rabbit Ray”, which is clearly a direct merging of a certain species of sea slug and an Eagle Ray. I would call this a Frankenstein Fusion and I mean something very specific with that. To me a “Frankenstein Fusion” is a fictional being that is created by directly taking parts from real life creatures and putting them together, without any consideration of how it could have evolved on its own accord. This is not very promising and a bit fishy, to be honest, but let’s push onwards! What is striking about the fauna in general is that there are a bunch of creatures that resemble “fish” and often have names reflecting that semblance. There are Holefish, Hoopfish, Bladderfish, Garryfish, Spadefish, Spinefish and Crashfish, to name a few. However, there is very little continuity in the number of fins and their placement, and neither in the number of eyes or even the presence or absence of a mouth. So there is no consistent body plan which would otherwise enable you to group these so-called fishes into one or more classes. Even species that appear to be closely related still have differences between each other that are so fundamental that it becomes very hard to keep them together.

Take for instance the Boneshark. A fascinating creature that looks like a shark covered in plates. It is reminiscent of the Placoderms from Earth which are early jawed fishes with a bony armour. Unlike Placoderms, the Boneshark swims in a whale-like manner with a tail fluke and seems to have a segmented exoskeleton.

Boneshark. Source: Subnautica Fandom Wiki

There is another creature in the game called the Sandshark that seems similar, but upon closer look, many problematic differences come to light. To begin with, there are differences in the number of eyes and the number of segments. The placement of the pectoral fins is also off, because it is associated with the second segment in the Boneshark and the first segment in the Sandshark. What’s more, the Sandshark possesses two rows of caterpillar-legs on the ventral side, whereas the Boneshark does not. Of course, some of these differences could be explained by loss or fusion, but they’re still very fundamental and the Boneshark and Sandshark can thus only be distantly related. The Sandshark actually looks more like a cross between some kind of real life predatory fish and an extinct sea scorpion like Eurypterus. So perhaps this is another example of a Frankenstein Fusion?

Sand shark. Source: Subnautica Fandom Wiki

Something similar is going on with two other species, the Oculus and the Peeper. They look so much alike that the impression is created that we are dealing with two closely related species here. Apart from similarities like the eyes, lateral openings or holes in the side, and a dorsal and ventral tube for propulsion, they’ve also got a very similar body shape and overall appearance. But on the other hand, the Peeper has a beak and the Oculus has no mouth whatsoever. Also, the Peeper has a tailfin like a fish, whereas the Oculus has backwards-pointing “stalks”. The creators clearly wanted to make two similar species, but the differences they added are just too great in my opinion. Now we could have a lot of fun putting species together or tearing them apart, but it is still a bit of a subjective exercise that would take a lot of time.

But there is actually a more objective way to look at the entire fictional fauna to see to what degree it looks evolved or is just a Frankenstein Freakshow. It is called a phylogenetic analysis. This is an algorithm that is normally used to reconstruct the evolutionary relationships between real-life species, but we can use it here to see if any of the Subnautica species cluster together somehow, or if it’s all a mess. So I went about meticulously coding each species’ specific characteristics in a so-called character matrix to run through a phylogenetics program. The program calculates those evolutionary trees that are the most likely. To my surprise, the results were better than I expected, although there are still many issues. All in all, a 130 equally likely trees were found. From these, this consensus tree was distilled.

What we already can see is that most of the typical fish-like creatures are nicely grouped into a single branch. Those creatures that are more dolphin-like in their mode of swimming by means of a fluke or vertical tail fin are also held together reasonably well in their own branch. And the same goes for all the ray-like creatures down here, including the rabbit ray! Also a nice grouping is formed by arthropod-like creatures like the Crawlers, Sea Treader and Crabsquid. We do have a lot of unresolved relationships at the bottom of the tree, as well as some oddities. For instance, we have the Hoverfish ending up together with the Ghost and Reaper Leviathan. And the mouthless Oculus, despite being very similar to the Peeper, is put together with the Bladderfish instead, which is also mouthless. We may need some more characters to sort out all these different placements.

So how reliable is this evolutionary tree? Well, its consistency index is very low at 0.39 and there are too many equally likely trees. It’s pretty clear to me what the problem is. First of all, there are too few characters compared to the number of species; only 36 to 43. There should be at least twice as many characters to be able to properly sort out the species.

What it comes down to is that there are too many anatomical details that we simply are lacking! We’ve literally only been able to go skin deep. A few of the X-ray images show in-game hint at some creatures at least having a backbone, but we still need to know all of the species that have an internal skeleton and what its precise structure is. We also don’t know which of the different kinds of eyes and fins etcetera are derived from the same ancestral organs. Is the single eye of a Cave Crawler the same as that of a Spadefish? Clearly, there is a lot of room for speculation allowing for the invention of a fitting evolutionary history for the entire fauna of Subnautica.

If you would like me to go more in-depth with this, please leave a comment below.

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