Mesotylos

I remember still one of the very first expeditions I undertook on Ryl Madol. I was still a young researcher, given rather mundane tasks. There was an area close to the coast that was designated as relatively “safe”, where I routinely documented the local population and diversity of carnivorous cycads (yes, the plant, not the insect). Technically it was a task I could have done by myself, I knew my way with a gun in case any dangerous animal might have appeared, but, of course, the research base did not fully trust me, so they signed up one of the hired mercenaries to escort me each time I went. It was pretty simple. We donned our gasmasks, took a small motorboat out from the base islet and drove it upriver to the research area. Most days were quite peaceful. Most of the big, scary things live further inland and most of the aquatic life gets scared by the sound of the boat. The guy, Johnson, was sadly not that talkative. He seemed rather annoyed to be my “babysitter”. He often just sat there on the boat, gun in hand, and quietly watched me as I walked around on shore and studied the plants. The plants, you ask? Oh, they’re only dangerous if you are a bug. Ryl Madol may be full of biological wonders but even it doesn’t have man-eating plants straight out of Hollywood. At least as far as we have observed.

So, there I was one day, counting cycads (or were they benettitaleans?), when, absentmindedly, I moved a little outside the research area and, out of the view of Johnson, deeper into the forest. I just roamed around a little when, suddenly, three men walked out of the underbrush and circled me. Their faces, like mine, were obscured by gasmasks to protect against the toxic spores. They looked rugged and they carried high-calibre weapons. One of them, visibly unwell, had an insanity fish still stuck to his neck. I’m not even sure he noticed the death sentence, perhaps he was this numb from all the pain he had already endured. They clearly were not my guys. They were stalkers, come here to raid the island for artefacts. Sometimes they kidnap or take hostage unsuspecting scientists, thinking that we have more secret knowledge on where to find the good stuff. Today it seems it was my turn. I tried to cry out for Johnson, but one of them put a gun to my head before I could even raise my voice. I knew I’d be dead if I screamed. They asked me if I knew where the “Dream Pool” was. I did not know what that meant and to this day I still do not. But of course they thought I was lying and began to beat me up. My mask nearly broke. In that moment, out of the corner of my eye, I saw something moving between the trees. It was some sort of translucent shadow, either camouflaged perfectly or nearly invisible. But I could sense some kind of movement between the tall cycad trees. Out of raw nature itself, it seemed, two hooked arms materialized and pierced through one of the stalkers, lifting him into the air like a praying mantis would a fly. My first thought was some kind of mantiraptor, but we have never seen those being able to change their colour. Though maybe that is exactly the point. The poor guy, claws pierced straight through his shoulder and belly, screamed like hell. He tried to lift his gun and shoot wildly around. I don’t know what his plan was, he was probably not thinking at all in the moment. By a mere miracle he missed me and instead it was now one of his stalker buddies that ended up screaming and bleeding out on the forest floor. The third guy lifted his gun and tried to shoot at the invisible arms puppeteering his friend, but before he could even pull the trigger, something else grabbed him and dragged him silently into the jungle.

The next moments are blurry to me. For unknown reasons I was spared by the ambush and was able to run back to the river. Johnson was sitting there, waiting for me. It was as if nothing had happened. He sat there, upright, with his wannabe military-uniform, oar of the boat’s motor in one hand, the other hand on the pistol holster, ready to pull on any unsuspecting foe. But there was just one problem. His head was gone. Ripped clean off, no trace of it in sight. I don’t think I even saw any blood splatter on his clothes, at least not in the heat of the moment. I did not really have the time to think about how morbidly bizarre that was, I just pushed the boat back in the water, pushed his body out of the way and started the motor. Downriver I think I took a few wrong turns and suddenly ended up in some quite bad, rocky rapids. I crashed the boat and flew overboard. All I can remember next was floating out at sea, not too far from the coast. The current must have swept my unconscious body out. I took my mask off to get enough air.

As I was contemplating my options, perhaps trying to swim back on shore, that wass when I saw it approach me. The huge shadow of a Mesotylos, a nearly 10 metres long carnivorous marine reptile, slowly drawing near me from beneath the waves. I could see it undulate up and down through the water, swinging its large, wing-like fins up and down, like a humpback whale. The long, crocodile-like maw turned towards me and I just knew I was done for. There was no way for me to survive this encounter. I just leaned back in the water and pretended to be a corpse, in the faint hope that it might lose interest. 

The strangest thing then happened. I could feel it poke me with its snout, me doing my best to remain stiff and not panic. I could feel it nudging my body. But it did not attack. It placed its head underneath me and then gently lifted me above the waves. I could feel it breathing through its retracted nose and I sure as hell know that it felt me breathing too. But that is all it did. Lifting my body out of the water and just gently float there with me, for what felt like an eternity.

Eventually I heard a boat approach and, thankfully, it was one of our own research vessels. As the sound drew closer, the reptile sank into the depths again and left me alone. The crew had seen me and were able to pick me up right after. To this day I still think about what happened. Why am I not dead, a pile of half-digested bones at the bottom of the ocean? Was the animal just not hungry? Did it not recognize me as food? Was it just curious? I cannot help but be reminded of those old stories of sailors being saved from drowning by dolphins.

As the name implies, Mesotylos is a mesosaur, as far as could be gathered from stranded specimens. Yes, a mesosaur. Not a mosasaur. Mosasaurs were true marine lizards of the Cretaceous, whereas mesosaurs were much more archaic beings of the Permian period, the very first marine reptiles (though in some phylogenies they even end up on the synapsid side of the amniote family tree). In a world as stuck in the Palaeozoic as Ryl Madol, it is perhaps no wonder that such animals survived here and continued to evolve. Very obviously, Mesotylos and kin have managed to make the full shift into fully marine life, as have many amniotes that came after them. Unable to move anymore on land, they have completely reduced their hindlegs and their forelimbs have become elongate flippers perfect for “underwater-flying” as is also seen in penguins and the extinct plesiosaurs. Uniquely for any amniote, this style of underwater-flying is combined with a vertically undulating, horizontally flattened tailfluke, very much like that of a manatee. Also very strange is that each flipper still retains two prominent claws, something not seen in any other fully marine reptile or mammal. Perhaps these do serve a function in mating, or maybe they have some hydrodynamic effect. Speaking of mating, their reproduction remains unknown, though it is generally assumed that they give live birth, unlike their egg-laying ancestors. Based on the shape of the very crocodile-like snouts, it is also generally assumed that they feed on fish and various other aquatic vertebrates, which makes my survival all the more miraculous.

Apart from this, nothing more can be said about these mysterious animals, as they are rarely encountered in life. Cryptozoologists like Bernard Heuvelmans have suggested that Mesotylos may be the origin behind various sea serpent sightings all around the Indian Ocean and Southeast Asia. While that idea may at first seem compelling, there is so far no solid evidence that the unique fauna around Ryl Madol’s coast has ever ventured to other areas of the globe, unless by human means. It is as if some strange force binds the animals to the island.

Regarding the little “reef friends” I depicted the fellow with: On the very right we can see one of the many strange brachiopods that inhabit the island’s waters. Its long stalk makes it resemble early Cambrian stem-forms, like Yuganotheca, however this appears to be a case of convergent evolution, as it is found to be a true rhynchonellid.

Emerging below it from a small tunnel is a Dermichthys, nicknamed “Dunkeelosteus”, a small antiarch placoderm with an elongated body that lives much like a moray eel, hiding in reef burrows and ambushing prey. Swimming below it is one of the many marine centipedes that swarm the island’s waters, as well as an ophiuroid brittle star.

More interesting is the Arboreaites and her offspring on the lower left. All research indicates that this seems to be a bona fide arboreomorph, a type of Petalonamae from the Ediacaran or Late Precambrian. This makes this unassuming frond actually one of the most interesting organisms in this picture, as it is the most ancient organism on show here. Tests done on these organisms have validated many hypotheses that had already been suspected about the fossil relatives: 1) They are indeed true, diploblastic animals, however outside crown-Eumetazoa. In other words, more derived than a sponge, but still more archaic than a jellyfish (though some genetic tests intriguingly recover it as somewhere near the base of Ctenophora). 2) It is in fact a colonial organism composed of multiple zooids, which together constitute a holdfast, a backing sheet and the many lobed filter-feeding “pods”. The central stem itself that is keeping everything together it in fact a bundle or fascicle of stolons protruding from all the pods. Very intriguingly, the individual zooids of Arboreaites, stuck on the inside of each pod, resemble miniature versions of the solitary rangeomorph Charnia. As can be seen Arboreaites can reproduce asexually using stolons along the ground, very similarly to bryozoans anc cnidarians. However, sexual spawnings have also been observed, where the organisms release eggs and sperms into the water. Even though the organisms lack true gonads, they appear to be able to produce these gametes from undifferentiated body cells, much in the manner of sea sponges.

It is extremely intriguing that Arboreaites survives and even thrives around the reef regions of Ryl Madol, despite plenty of competition with supposedly “better” Palaeozoic life. This brings into question many leading hypotheses about the extinction of these organisms elsewhere in the world during the Cambrian. One wonders what Earth’s oceans might look like if more of these had survived. Now that would be a fun scenario to think about for the enthusiasts of this new-fangled gene I heard of. I think they call it “speculative evolution.”

Neothelodonts

First appearing during the Late Ordovician, thelodonts were once one of the most successful groups of jawless fish, their distinctive scales being one of the most common index fossils for the Silurian. But the fate of any group that is successful is that, at some point, they simple are not anymore. Thelodonts vanish from the fossil record by the Late Devonian, along with most other jawless fish.

Such is not the case on the lost world of Ryl Madol though, where small thelodonts still swarm the waters of the coasts and rivers. Their success story seems to have continued here, where, despite still being jawless, they have managed to expand into all kinds of ecological niches.

Original monochrome

While Thelodonti as a whole may have been a paraphyletic group, perhaps a transitional grade between Heterostraci or Anaspida on one side and Gnathostomata on the other, most or all of the Rylian thelodonts seem to descend from the monophyletic group Furcacaudata. As the name implies, they are all unified by their characteristic tailfin. It is composed of a forked bone, from which sprout multiple, rigid rods, each suspending a membrane, a bauplan not seen in any other fish. Apart from this trait, Neothelodonti, as this island group has been named, varies a lot in morphology and appearance, making their internal classification unclear. A few have paired fins, though it is unclear if these are homologous with the pectoral fins of other fish. It is also unknown if those that lack these fins completely lost them secondarily or never had them in the first place. The same goes for dorsal fins. A few, in lieu of true jaws, have evolved a radula-like tongue, though it is again unclear if this is a shared or convergent trait.

The perhaps most unchanged of the neothelodonts is Aureocauda rylensis, which looks virtually identical to relatives like Furcacauda from the Devonian, except for the fact that its mysterious paired fins are more developed. It can be found suspension-feeding at various water-levels off the coastal reefs.

One of the largest neothelodonts is Biceratopsis albus, a hand-sized, triangular fish with two rhinoceros-like horns growing from its head. It is unclear what these are used for, as they do not seem to be a sexually dimorphic trait. This rhino-fish sports one of the least unusual mouths of the neothelodonts and as such it is most often encountered suspension-feeding in the open water of the reefs.

This is in contrast to the smaller Proboscichthys hippotigris, who is another reef-dweller, but one that mostly swims close to the ground. Its mouth forms a downturned nozzle or trunk, which it uses to sift the soft mud for any detritus that has fallen down from the upper water layers.

Highest in the water-column feeds Gleptodus ridens, in which the furcoid tailfin makes up over half the bodylength. This seems to make the body rather stiff and spiny and in turn also harder to swallow for predators. Also unique for a thelodont is that it has evolved a sort of expanded lower lip, giving it the appearance of a fake jaw. This seems to be an adaptation towards filter-feeding on planktonic algae floating close to the water’s surface.

Swimming at about the same height is Neothelodus homocercus. It is a fast swimmer which mainly feeds on zooplankton, such as copepods and brachiopod larvae. Due to its elongated shape, strongly contrasting with the other neothelodonts, it has been proposed that it actually falls outside of that clade, not being a furcacaudatan but instead being more closely related with the other major Palaeozoic clade Thelodontiformes.

Levicercus rufus is an adorable little fellow that shares some behavioural traits in common with clownfish, mainly the fact that it lives in symbiosis with local sessile cnidarians, including not just anemones but also rugose horn corals (another Palaeozoic survivor of the island). The fish is immune to the their nettle-stings and uses their tentacle-crown as a sheltered home. In turn, it feeds on small radiodont and trilobite parasites that might attack the anemone. On occasion it has even been observed guarding its home against marine dicynodonts, who, just like sea turtles, can feed on the cnidarians with their hardened beaks. Being jawless, Levicercus’ main method of attack against these giants mainly lies in being as annoying as possible, harassing the eyes and face of the synapsid. Unlike clownfish, Levicercus are not social and do not form hierarchical family groups. Each horn coral instead seems to be inhabited by only one or two of the fish, indicating some territoriality.

Hypersubcercus aureus shares a similar association with corals, though in this case living between them rather than in them. It is also more commonly found among tabulate corals, as well as strophomenid brachiopods. With its radula, it mainly feeds on the algae that grow on the shells of these invertebrates. The fish are surprisingly territorial over their grazing grounds, using their hyperelongated lower tail-lobe as striking weapons against unwelcome intruders.

Echineidion ramjeti is comparable to a remora, using its torpedo-like shape to follow and trail behind larger marine animals, be they sharks, acanthodians or mesosaurs, in order to feed on their parasites and loose dead skin with its downturned mouth. It is one of many finless thelodonts, though it is uncertain if these form a unified group. Its shark-like, pointy nose is unique among thelodonts.

Another commensal feeder is Capronia arcuata, which is also finless. Instead of chasing other animals for their waste, it waits for them to come to it. A mated pair of Capronia usually “set up shop” at their own territory in the reef and wait for larger animals to stop by and rest, letting themselves get cleaned by the little fish.

Adontus homocercus is a freshwater-dweller, inhabiting most of the vast inland waterways that innerve the island. Being small, living in murky waters patrolled by far more dangerous creatures, it is not any wonder that very little is known about this fish. The first descriptor of the animal originally wanted to name it after its distinctive three-humped dorsal fins, bafflingly calling it Triceratops, until he had to be informed that there was already a genus of dinosaur with that name, leading to a minor éclat with the ICZN and a subsequent broken nose when unable to accept that fact.

Monocauda is another freshwater thelodont genus, but much more widespread than Adontus and encompassing at least seven different species. It is most closely associated with swamps and mangroves and feeds on the abundant algae and detritus there, itself being prey to the various tadpoles and efts of the anamniotes. It is unique for having lost the distinctive fork-shape of the tail, having only the upper lobe left, with the little finlets extending all the way down to below the head and moving the animal forward in an undulating motion. It is perhaps this adaptation which allows it to be so successful, making it far more flexible, mobile and better able to hide and shelter in the various nooks and crannies of its environment.

Orthrocaris

Ryl Madol is not just a nightmare for its brave explorers but also for the average taxonomists, whether they study the animals live on the island or preserved in formaldehyde from the safety of their comfy university offices. Evolution has taken its very own unique path here, often with entire groups which are elsewhere only known from fossils. The end result are thus forms and combinations which defy all of our anatomical borders.

One of the most enigmatic of these is little Orthrocaris antebabylonensis, or Insanity Fish, curiously often found swimming within the pools and swamps which form at the center of the ancient, ruined plazas and their flooded sewers. There can be no other way than to simply describe it as a chimaera. At the front, a soft, bivalved, gill-bearing carapace, very much like in a phyllocarid crustacean, gives rise to two segmented arms and a head with two compound-eyes. So far, so arthropod. But then the mouth is ringed by four or more unsegmented little tentacles, very much like in a cephalopod. The hidden mouth itself is a single claw-shaped mandible similar to that of a velvet worm. Behind the carapace then emerges an elongated, eel-like body, with a dorsal and ventral fin running down its length. Though this body is soft, on the inside it contains a stabilizing organ which unmistakably resembles the chorda dorsalis of our own phylum. What can be said of such a creature which wildly mixes traits or arthropods, cephalopods and chordates? It is the invertebrate(?) equivalent of a platypus.

That nobody has been quite able to shoehorn this little monster into any taxonomical drawer is not surprising. Some claim the arthropodal characteristics outweigh the others, arguing that this may be some archaic member of that phylum that simply evolved the other traits through convergent evolution. Others argue that a chorda dorsalis classifies Orthrocaris automatically within the Chordata. The truth may literally lie somewhere in-between. Some have noted a resemblance to the Cambrian organism Nectocaris, which used to be similarly reconstructed as a chordate with the head of a bug. However, these reconstructions have long been deemed erroneous, as better-preserved fossils of the organism instead suggest that Nectocaris looked more like a flattened, two-tentacled squid. The resemblance to old reconstructions may thus only be a coincidence. Others have suggested a possible affinity of Orthrocaris to the Vetulicolia, who did greatly resemble an odd mix of arthropod and chordate. The cladistic placement of Vetulicolia is itself highly debated and no known vetulicolian fossil is known to have possessed limbs or tendrils as Orthrocaris has, so this affinity also remains entirely speculative. Said limbs most resemble the scourges of Cambrian legless arthropods like Leanchoilia. If recent genomic studies turn out to be true and Deuterostomia is indeed not a true group, then Orthrocaris may be the descendant of some unknown basal group of the alternative chordate-protostome clade Centroneuralia. In other words, it could, in a sense, literally be the ancestor of all groups discussed. Perhaps it could even be the result of some hybridisation accident, back in some dark Cambrian days when the genomes of all the phyla were still similar enough for such taxonomic bastards to come into existence.

Regardless of its classification, contact with Orthrocaris should be avoided at all costs unless one is properly protected. Although the organism is only as large as an index finger, the bite of some individuals is lethal. Not because it is venomous. For some unknown reason, the saliva of the organism carries a prion inside it. Prions are misfolded proteins, which can cause other proteins to misfold in the same way, allowing them to pathogenically reproduce almost like viruses. There is no known treatment method for prion diseases, so 100% of all infected end up either dead or severely disabled for life.

Like mad-cow-disease, the Orthrocaris-prion is neurodegenerative, meaning it attacks the human brain. It can lead to insanity, followed eventually by brain-death. Some infected have been reported to have escaped their containment and in a mad rave wandered out into the island, only to return days later, with almost no scratch on their body. The animals on the island (who seem to be immune to the prion) show no interest in attacking infected humans. Most shockingly, those patients who escaped without a protective mask on suffered no ill effects from the island’s toxic spores. It seems almost like a sadistic twist that only this disease grants humans the ability to survive on Ryl Madol, but at the price of a short life of insanity. The Headtakers, never too fond of outsiders, have by now discovered the disease’s cause and effect and weaponized it. Using the snake-like glottis in their lower jaw, Headtakers are capable of using blowpipes. When they are feeling especially sadistic, they will carry a leathern waterbag full with little, living Orthrocaris with them, remove the “fish’s” tiny arms and shoot them through the pipes at the necks of unsuspecting humans.

The most bizarre aspect of the prion is just how it cripples the brain. In most cases it mainly affects the areas responsible for language processing, making the infected eventually incapable of talking in coherent words or sentences. Instead, they all start spouting completely unintelligible gibberish. However, all those infected speak the same gibberish and seem to be able to understand each other to some degree, while suddenly incapable of understanding their healthy colleagues. In the early stages of the disease, before they lose the capability of speech completely, they can be heard in their quarantine cells seemingly conversing with each other in undecipherable but still distinctive words and phrases like “Oadriax!”, “Dilzmo!”, “Cordziz”, “Agtoltorn parach asimp!”, “Pappe hasatan, pappe hasatan aleppe” and “Rahel mai ameche zabi almi”. I imagine this must surely be of interest for neurolinguists, but they have not returned my calls.

Castorosaurus

Ryl Madol is able to support a large amount of amphibious and aquatic life thanks to its many pools, ponds and streams which pay tribute to large lakes and rivers. For many of the tetrapods and arthropods, these are vital for their reproduction, as their eggs and larvae lack shells and need to be laid in water. However, many of these breeding pools are not necessarily provided by the island topography. They are made by the wildlife itself, though, ironically, not by amphibians.

Encountered in almost every waterway are waterlogged wooden structures, which early explorers at first mistook as as bridges or fish-traps created by the island’s intelligent natives. But no. These are dams built by an aquatic reptile called Castorosaurus, whose name literally translated to “beaver-lizard”. Castorosaurs are derived members of the Captorhinidae, a group of Palaeozoic reptiles that, on account of missing postorbital windows, were traditionally grouped with the “Anapsida” alongside the turtles, though recent work has recovered them as being eureptiles close to the Diapsida. Even more recent work has declared them stem-amniotes, though this remains controversial.

Just like beavers, castorosaurs are ecosystem-engineers who prolifically build dams along narrow waterways, creating many pools throughout the island in which other organisms can thrive and reproduce. Their dams usually have a hollow chamber that can only be accessed from underwater. Here the castorosaurs lay their eggs and raise their young. The dam structure prevents terrestrial or aerial predators from easily gaining access to the nest, though the parents still tend to be on the look-out for any of the creeping amphibians that may dive and slither below.

Unlike the terrestrial captorhinids of the Palaeozoic, castorosaurs feature many aquatic adaptations such as webbed feet and a dorso-ventrally flattened tail like a platypus. This tail-shape is of course quite curious, as reptiles usually swim through sideways undulation and so one would expect a laterally flattened tail, but the tail seems to be mainly used as a sort of hammer in dam-building. What castorosaurs have retained from their ancestors are the long, kinked snouts with specialised teeth at the front. Said teeth have become quite large and spiky. Many people easily make the mistake of assuming that castorosaurs used their large front-teeth just like beavers to gnaw at wood, but that is in fact incorrect. They are entirely unsuited for such a task and are instead used to capture fish.

If they cannot gnaw at trees and branches, where do castorosaurs get the wood for their dams then? The answer is that they simply pick it up from the forest or lake floor and so do not need to saw up fresh wood. But why it is that simple for them is actually interesting. Vast areas of Ryl Madol are covered in thick carpets of wood-litter that degrade into smaller pieces over time as animals trample over them, but never truly rot and decay. Some pools and moors have as a consequence devolved into large, malignant peat bogs in which unwary animals may stumble and get trapped. It is highly unusual and not something seen in any other forests in the world. Only recently has the reason behind this been revealed by botanists and microbiologists: Ryl Madol entirely lacks any organisms, be they bacteria or fungi, that can digest lignin, the main polymer that makes up wood. This used to be true for all of Earth in the Carboniferous period, from which huge coal deposits still survive. While it explains the primordial nature of Ryl Madol’s forests, it just opens up many more questions. Why has lignin-digestion never evolved or arrived on Ryl Madol? Or did it exist here once but the respective microorganisms have since somehow gone extinct? The lack of notable coal deposits in the island’s geological formations may be evidence of the latter, pointing towards this being a fairly recent development. It seems almost like time on the island is moving backwards.