Acanthoracosaurus

A fierce giant walks through the forest clearing. The anoplosaurs and even the gorgoraptors stay clear off its path. The reptile’s claws are sharp and its head huge, sporting powerful jaw muscles. It bears no teeth, yet its tortoise-like beak is sharp enough to bite a man’s head clean off. Its bony brows have frozen its demeanour into one of permanent anger. Despite its fierce appearance, Acanthroracosaurus jobini is a herbivore, but that does not mean that it is harmless.

On an island inhabited by predators as large as some of the most gruesome dinosaurs from the fossil record, a moving hunk of flesh this large cannot afford to be placid. As if the claws and beak were not already enough of a defensive weapon, the back of the animal is covered in a carapace, arranged in a unique stegomorph pattern, where huge bone plates covered in keratin overlap each other like shingles on a house roof. If a predator such as Basilosuchus were to attack from the top, it would break against the carapace, maybe even get impaled by the double-row of horn-spikes that run down the back. If it were to attack from the side, it might get stabbed by the sharp, pointy tips of the shingles. Many a predator has met their death at trying to crack this tough nut open.

Even with its armour, the saurian does not afford itself leisure. At even the faintest signs of threat it may show aggression, though thankfully rarely without warning. Sometimes it will even walk towards predators it sees in its vicinity to attack them, perhaps thinking that offense is the best defence. This is why even some of the most fearsome predators like Decarnodon, who could theoretically bite through its armour, stay clear off the plated reptile. It is simply not worth the risk of injury.

When not in a fighting mood, Acanthoracosaurus can show other sides of its personality. Most of its day is spent mindlessly eating away at tough vegetation, sometimes even tree stems and bark, which it can bite through like butter. It has no teeth, but its digestion is aided by a rough rasping tongue and gastroliths lining its stomach. It can also often be spotted taking a dive in the island’s many waterways, perhaps to wash itself off the many parasites on its hide, the one enemy even its armour cannot do much against. Its breeding behaviour is somewhat peculiar, in that it actually resembles that of some flightless birds. A male and a female will find each other and mate, the female will lay her eggs in a nest that the male has prepared and then leave. The male is then left to care for the chicks by himself until they are old enough to live alone, though it is difficult to imagine a father more capable than a living fortress.

The origins of Acanthoracosaurus have remained mysterious until recently. While it outwardly resembles the common image of a dinosaur, it bears little actual characteristic traits of one apart from the upright bipedal gait. With its toothless beak, anapsid skull and carapace, some early theories have actually suggested it may be the descendant of some kind of proto-turtle, such as Permian Eunotosaurus. However, the osteoderms are not fused to the ribcage, making this unlikely. Other suggestions have been put forward, such as it being a squamate, archosauriform, pareiasaur or even a cyamodontoid placodont re-adapted to land. The discovery of two vestigial toe bones of digits I and II in the padded foot of the beast have opened up a new and much more likely possibility, which is that Acanthoracosaurus is a giant member of the Eubolosauria, albeit in its own family, Cheloniopsidae. In this regard it is interesting that it is often seen gregariously living with its much smaller relative Pointilisaurus. The small herbivores likely seek the giant out for extra protection, while the beast itself seems to tolerate them, though without a clear benefit from the relationship. Except for the few times when it itself snaps up one of the hapless little critters. While it may be mostly herbivorous, even it will occasionally eat smaller animals as an extra source of protein. That includes humans.

Pointilisaurus

Ever since naturalists have first set foot on the island, they have made note of a variety of small, bipedal herbivorous reptiles running around. This being the early twentieth century with its limited understanding of paleontology, the reptiles in question were early on classified as genuine surviving relic dinosaurs, specifically of the small ornithischian types such as fabrosaurs or hypsilophodonts. But as their skeletons were more closely examined, and our understanding of fossil reptiles grew, it was recognized that the small runners on Ryl Madol were something else entire.

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One of the first clues was the structure of their feet. Ornithischian dinosaurs only had four toes, whereas the Rylian lizards have five. Moreover, ornithischians walked on digits II – IV, with the inner toe digit I being reduced to a dewclaw. The island reptiles, however, walk on digits III – V, with digits I and II being reduced. The same pattern is also seen in their hands. While the elongation of the outer digits is common in some reptiles, it would be highly aberrant in dinosaurs.  The skull of these animals finally negates any association with the Dinosauria, for it lacks the antorbital fenestra typical of archosaurs and the back of the skull is even in a partial anapsid condition.

The final clue came, surprisingly, from Germany, when in the Permian aged Tambach Formation was found the fossil of Eudibamus cursoris. This was a little bolosaurid, a type of parareptile related to the larger pareiasaurs. Its hindlegs were highly elongated compared to the arms, leading to many reconstructing it as possibly the earliest biped. The condition of the skull, as well as the arrangement of the toes, is mostly identical to the bipedal mystery reptiles on Ryl Madol. Today, there is consensus that these creatures are descendants of this often-overlooked little parareptile, having adapted to obligate bipedalism and a fast-running lifestyle convergently to dinosaurs. The names that have been given to this new group in the technical literature are both Eubolosauria and Hylobolosauria and there is dispute over which name has preference.

One of the most common and well-known of the eubolosaurs is Pointilisaurus sibbicki. It is a small, fleet-footed herbivore, about the size of a green iguana. Gregarious, it can often be seen in small herds browsing on the lowland meadows or the forest edges. The groups are loosely organized and they quickly scatter when a predator like Gorgoraptor strikes. Social interactions are minimal, though some researchers have noted that the reptiles vocalize when in groups through a strange, cat-like purring sound. How exactly they produce this sound remains debatable. Reproduction is quite simple. After mating, the female lays her eggs in a hidden nest in the ground and leaves the eggs to their fates. The hatchlings usually survive through strength in numbers alone, with many of the little lizards falling prey to the voracious jungle shortly after emerging out of the ground.

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While the most common eubolosaur on the island, it is also the most primitive, still sharing many traits with Permian Eudibamus, such as the iguana-like mouth with leaf-shaped teeth. Through anatomical and molecular studies, it has been revealed that many of the more enigmatic reptiles on the island can also be placed in the same group, however within a separate clade. These derived eubolosaurs have, in an even stronger parallel to some dinosaurs, evolved a predentary bone at the tip of their snout, giving them a sharp beak well-suited for chipping vegetation. These are the Aviopsia, which as of writing consist of three families. Saltopusauridae are small herbivores with parrot-like faces that move by saltation, similar to kangaroos or wallabies. The families Anatopsidae and Cheloniopsidae together form an even more derived clade, signified by the loss of the two inner digits of the foot, which for a long time obscured their relationship to the other eubolosaurs. Anatopsidae are huge, amphibious reptiles, with duck- or geese-like bills they use to feed on a wide variety of aquatic plants. Cheloniopsidae, such as the massive Acanthoracosaurus, are more terrestrial animals, which shield themselves against the island’s predators with strong, stegomorph armour and spikes.

While non-avian dinosaurs, as to our knowledge, still remain absent from Ryl Madol, these magnificent beasts are no less exotic nor less worthy of our awe.

Carrion Trilobites

Elsewhere in the world, fossil traces of trilobites living in freshwater, let alone venturing onto land, are scarce at best. On Ryl Madol, land trilobites are curiously quite common. In some respects, their evolution here was likely easy, in other ways hard. Like their cheliceratan uncles they were able to evolve simple book-lungs by invagination of their gill-arms into their body. However, what must have been a great challenge is their lack of true mouth-parts, compared to the wide range of mandibles and cheliceres of their cousins. The closest thing they have is a hypostome, which acts more like a backwards-pointed spade or shovel rather than a jaw. This is not a big problem when living on the ocean floor, where microscopic detritus constantly rains from above, but land-life does not grant such luxuries. As the myriapods prove, even feeding off leaf-litter requires mandibles. Facing jawed competition from not only centipedes and arachnids but also the great barage of insects, it is perhaps for this restraint why elsewhere on Earth trilobites were never able to make the big leap onto land, dooming them to an oceanic existence where they would eventually meet their end once marine environments became near-uninhabitable in the Permian. On Ryl Madol the trilobites were able to carve out a few terrestrial niches for themselves, sometimes literally. The reasons for this are unknown but it has been speculated that it may be potentially due to the island’s distinctive lack of derived Neoptera insects, which may have given archaic arthropods more room to expand and adapt.

While some of the rylmadolian trilobites have adapted to feed on soft-bodied worms and nematodes, the majority of terrestrial trilobites are still detritus-feeders, living off the soft excrements and droppings of various larger animals through simple sucking- and shoveling-motions. These basically fill out the same ecological niches as dung beetles and scarabs would. While this may seem like a pitiful existence from a human perspective, it is actually quite a respectable job, as many a great pathogen and toxin meets their end in the robust glabella-stomachs of these critters, keeping the ecosystem healthy and safe from serious disease outbreaks. Still, at least one group has taken up a more savoury diet. The carrion trilobites are a special clean-up-crew that appears anywhere where a large vertebrate carcass lies, usually deep in the thermal chasms. The little critters possess a strongly reinforced hypostome shaped like a wood-carver. They use this to scrape off meat into easily digestible chunks and they are especially good at removing the last bits of flesh from bones. A large swarm of these can turn an ungainly corpse into a beautifully stripped and clean skeleton in under two hours. Rumours of them allegedly doing the same to still-living stalkers are almost assuredly a myth.

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.