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.

Sealacanth

As the sun sets and the waters calm down, a strange creature hauls itself onto a beach. Its limbs end in fins, yet they already have joints which foreshadow elbows and knees. Its two dorsal fins now hang to the sides, useless outside the sea. It breathes heavily, almost strained, but it is doing better than the other water-dwellers that have been swept here, dead ammonites, clams and fish, which have been crushed by the gravity and heat. It succeeds where others fail. Beyond the beach lies a lush rainforest, filled with big invertebrates. To the victor will go the spoils.

Only the presence of scaly, bipedal creatures on the beach and the distant cries of seabirds betray that this is not an ancient scene from the middle of the Devonian period. This is the very modern life of a particular fish on the island of Ryl Madol. The sealacanth (Erpetolepis littoralis) looks like an ancient holdover but is in many ways also something quite new, perhaps among the most advanced of the walking fish that live on Earth.

Despite the name and appearance, Erpetolepis is not a close relative of the coelacanths which also swim around in the Indian Ocean. The presence of internal nostrils and labyrinthodont teeth identify it not as an actinistian but as a tetrapodomorph, though closer to basal forms such as Eusthenopteron than to more famous fossils like Tiktaalik or the true tetrapods. Its many adaptations towards littoral life seem to be parallel developments. Unlike archaic lobe-finned fish, the sealacanth has clearly defined limb-joints, though not yet true fingers, instead just a flexible fan of lepidotrichia like other fish. It is a very subtle difference, but the shoulder-girdle is also not fully connected anymore to the skull, allowing it to move its head independently of the body, an important development which in true tetrapods led to the evolution of a true neck. It also sports fully developed lungs in addition to gills.

Actual seals are largely absent from the coastlines of Ryl Madol, on account of the presence of the toxic spores. While there is no shortage of aquatic and semiaquatic amphibians and reptiles on these beaches, very few of them have seemingly managed to utilized the resulting opportunity quite as successfully as these clumsy-looking fish, earning them their name. Like pinnipeds, sealacanths hunt in the shallow and open waters for food but when they want to sleep and rest, they come onto land and sometimes even sleep in groups. Though gregarious, they are not exactly social, as the lack of ears limits their ability to communicate. Towards human explorers they are largely apathetic, though some degree of curiosity is reported on occasion.

The prey of sealacanths consists of slow-swimming or crawling invertebrates and small vertebrates, largely fish, lizard-sized marine reptiles and washed-up carcasses. Sometimes sealacanths can be observed digging up the rocky nests of Spheniscodapedon, the penguin-like reptile seen here in the background, in order to feed on their eggs. This does not always go well, as these “rhynchoguins” tend to guard their nests and have pretty mean hooked beaks, more than capable of ripping chunks of flesh out of even a large fish such as this. Though it is larger and stronger, if a flock of these reptiles gangs up on a sealacanth, they can very easily rip it to shreds. The further the fish crawls into the island, the more dangerous the threats become and so too the farther out into the sea it swims. Perhaps being stuck, ecologically and evolutionarily, on the water’s edge is good enough, at least for now.

Walky Tully

Ryl Madol is already home to a variety of animals which by all rights should not exist, at least not anymore, but even among them the walky tully (Micrormus holidayi) stands out, as it has evaded proper classification to this day.

What really can be said about an animal whose jaw sits at the end of an extendable proboscis, has eyes on stalks like a snail, a body like a tadpole and three clumsy legs? It has a backbone, so at the very least it can be considered some kind of vertebrate, but that is where consensus ends. Unlike any other vertebrate, there is no direct bone-connection between the jaws and the cranium, the “neck” is just a floppy tube made of cartilage and muscle, attached to what resembles the hyomandibular bone of sharks. Despite living in water, it has lungs but no gills. Its “fingers” have no resemblance to those of tetrapods, instead having evolved from fin-rays, the internal anatomy of the forelimbs somewhat resembling the alternating bone-structure of lungfish-fins. The single hindlimb is located behind the cloaca, meaning that it is possibly homologous with the anal fin found in most fish. However, in the vertebrae, the pleurocentrum dominates, which is a trait more typical of stegocephalian tetrapods than of fish.

With its proboscis and stalked eyes, many researchers have obviously tried linking this animal to the notorious fossil Tullimonstrum gregarium of Illinois, which is where its common name comes from. However, the classification of Tullimonstrum is itself controversial, as it is not even clear if this organism was a vertebrate or an invertebrate of some kind. If Tullimonstrum was a vertebrate, it would have been one of the most basal cyclostome kinds, a relative of lampreys and hagfish. It notably has no fins whatsoever, at least none that were ever able to be identified from the fossils. If Micrormus is indeed a descendant or close relative of the tully monster, then it must have evolved limbs, lungs, a loss of gills and various other characteristics that are not present in its Carboniferous ancestor independently of other vertebrates.

This suggests that the resemblance is merely due to convergent evolution and that Micrormus is some kind of highly aberrant bony fish, possibly sarcopterygian in origin. Due to its amphibious characteristics, the most radical proposal has been that it may descend from some type of tetrapodomorph that, like the coelacanth, still possessed a muscular anal fin but for whatever reason had lost its pelvic fins, which in true tetrapods evolved into our hindlegs. This hypothesis is not at all popular, but other suggestions have not been less crazy, such as the idea that Micrormus is a vertebrate-mimicking cephalopod or a relative of the dancing worms of Turkana. Genetic studies that could shed more light on the matter are unfortunately lacking.

In contrast, the actual life habits of the walky tully are surprisingly unspectacular. It is a small animal, able to fit comfortably inside a human hand. Like most fish on the island it has developed an amphibious lifestyle and spends a lot of time crawling around or even sleeping on lake shores. When “walking”, the single hindlimb is not used merely as support for the forelimbs but also helps the animal push forward, earning it the alternative name “mud-tripod”. In the water it hunts smaller fish and tadpoles, such as the mantiraptor larva seen here. Some researchers have proposed that it actually is a specialized tadpole-predator, but there is no conclusive data that it prefers this prey over any other small aquatic critters. Among its own enemies are various stegocephalians, predatory fish and the stork-like gruisaurs.

Tullys reproduce through external fertilization and lay their spawn inside protected alcoves along riverbanks. The young hatch as miniature adults without first going through a larval stage, which is why gleaning its evolutionary history from embryological data has also proven difficult.

Carnoconodon

“Whoever digs a pit may fall into it, whoever breaks through a wall may be bitten by a snake.”

- Ecclestiastes 10:8

The deepest parts of the tectonic chasms will of course accumulate water in them. Nourished by the decay of leaf litter, rotting carcasses, gnawed bones and scavenger excrements, these ponds have turned into the most fetid of swamps. In the murky waters swim horrific creatures, often the descendants of marooned gut parasites and the most lowly and dreadful of scavengers.

Among the latter, species of Carnoconodon tend to be the most pugnacious. As the name suggests, these are living members of the conodonts, a group of jawless fish, vaguely reminiscent of the lamprey, with a bizarrely intricate tooth-apparatus. Having populated the seas from the Cambrian until the end of the Triassic they have proven themselves to be tenacious, but Ryl Madol is now the only place on Earth where they survive.

Carnoconodon has in some ways evolved a simpler mouth than its ancestors, it just being a yawning gape that opens up like a zipper. It is adorned by multiple rasping teeth on the inside with eight-to-ten large slicing teeth ringing its edge. Where it surpasses its ancestors is of course its size, growing up to a metre or two in length.

Carnoconodon is often characterised as a scavenger, scraping flesh off the carcasses of animals that have fallen down the deep chasms and died from the impact. This is not entirely accurate. If a poor victim survives its fall, these eels from hell have no qualms about finishing the job themselves, often attacking in swarms and slicing deep wounds into the flesh until it bleeds to death. Our dinocephalian here is finding this out the hard way.

Cancrichthys

Ryl Madol teems with all types of amphibious life in its many waterways. This includes actual amphibians, armoured proto-reptiles, various arthropods and even some derived sarcopterygian fish. But out of the swamps can sometimes also crawl a quite peculiar creature, which seems like a wild mix of all of the above. Cancrichthys zemani, whose name literally means “crabfish” is a placoderm, a member of an ancient group of armour-encased fish which went extinct elsewhere on Earth during the end of the Devonian period. More precisely, it seems to be an antiarch, unmistakenly related in some form to ancient fossil genera like Pterichthyodes or Bothriolepis.

What earns it its name are its unique limbs. Although, when viewed from the side, it appears as if it has six crab-like legs jutting out from the body, these are actually all attached to a main “fin”, a stylopodium. It therefore technically only has two legs, but this does not diminish the fact that no other type of vertebrate has such limbs, as it would correspond to a single upper arm/humerus out of which multiple lower arms sprout.

When on land, Cancrichthys breathes using a simple lung, which gives credit to the controversial idea that fish like Bothriolepis already evolved this trait independently of the ancestors of tetrapods. It seems therefore possible that these ancient placoderms were already somewhat amphibious creatures sifting through mud in lakes which regularly turned oxygen-poor. Evading extinction on what would become Ryl Madol, time could have put more selection pressure on the limbs to become more capable of terrestrial locomotion, in order to travel between ponds and lakes more easily. As antiarchs like this had no autopodium (what becomes the hand in tetrapods), evolution had to make-do with what was available. Even if unique, the mutation that leads to Cancrichthys’ odd limbs may be similar to the hox-genes that split the tetrapod autopodium into fingers, but instead applied one level higher to the zeugopodium. As Placodermi are a paraphyletic grade from which all later bony fish, including us, likely descended, it does not seem implausible that the genetic tool-set for this could have already been present or re-evolved in these fish.

Cancrichthys leads an unassuming life, most of it spent plying mud for invertebrate prey, such as worms, snails or freshwater trilobites. On land, its carapace gives it perfect protection against most predators. If that is not enough, the fish has sometimes been seen striking at threats with its tail. Like many of the fossil placoderms, Cancrichthys reproduces through internal fertilization and gives birth to live young. This is in a somewhat humorous contrast to many of the more terrestrial, reptile-like creatures of the island that have to lay their eggs in water.