This is @a-beepbop and I’s renditions of the 1,000,000 year old Ancient Skeleton from Subnautica (which I will now refer to as the armored leviathan from now on).
This sucker is probably one of Subnautica’s biggest biological mistakes. It had both an endoskeleton and exoskeleton, yet the endoskeleton has fused to the exoskeleton and is barely visible. It has no nostrils (which is a reoccurring problem in Subnautica skeletons). The lower jaw has no attachment point to the skull and would have barely been able to have opened due to the shell getting in the way. It was so heavy that I doubt it could swim. The skeleton has groves in it that serve absolutely no purpose (other than being a rather pathetic attempt at trying to look cool). And finally the most obvious goof… the stupid holes that serve no purpose.
Now I often like to brag about how I’m a freakin’ wizard at biology, and how if you gave me a fictional creature and told me to give you a run down on it’s biology, then I’d go to insane lengths to describe the external anatomy and biology as well as the possible internal anatomy. But this?! I had no idea what to do, and I was so stumped that I had to call up my good friend @a-beepbop and spend an entire night speculating about what this thing even is.
But we finally came up with two theories that work.
My theory is that the armored leviathan was a slug-like filter feeder, and that the weird holes were actually modified gills. It would have propped itself up on ledges and sucked in zooplankton rich water through its mouth, while the giant scary looking teeth really just kept things out of its mouth that were too big to be eaten (as well as looking scary to any predators). I provided a side view of the head and armored gills, as well as a sketch of it feeding during an algae bloom. This sketch is actually a modified and colored trace over of a sketch that @a-beepbop made (I did it with their permission and have provided a picture of the original sketch that they made).
The second theory is something that @a-beepbop briefly suggested. They mentioned that it might be an unfortunate individual affected by an incredibly rare disease called Fibrodysplasia, which is a very rare disease where fibrous tissues (like muscles for example) turn into bone when damaged. Now if this is the case then it would explain why the armored leviathan skeleton has those weird groves on it. Despite the fact that we agreed that my filter feeding slug theory is probably more likely, I actually like their theory more than mine. They also made a sketch of what they think a normal armored leviathan would look like.