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.

Mantiraptor

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A reptilian brushes through the thicket. Small and lithe, standing on three-toed legs, the little herbivore seems like a mix between a lizard and a naked bird. This eubolosaur mindlessly nibbles on some ferns when, suddenly, two large, slimy arms materialize out of the forest, clamp down and pick it up. The prey’s futile attempts to flee this deadly grasp only dig the huge keratinous spikes and hooks lining the arms deeper into its flesh, as two-clawed paws curl around its belly. Well-placed bites to the back and neck soon end the bleating cries.

The ambusher is Mantiraptor olsoni. Though it also appears like a two-legged lizard, it shares little else in common with its prey. Its skin is smooth and clammy and it has no claws on its feet. Instead of an earhole there sits a large tympanum behind the skull, like a frog’s. This man-sized forest monster, like many others on Ryl Madol, is an anamniote, not quite a reptile, but also not quite an amphibian.

The retention of metamorphosis in these once-archaic tetrapods has allowed for some quite impressive plasticity in the development of the limbs, both through phylogeny and ontogeny. Unlike any reptile or mammal, this predator has been able to modify its forelimbs through the fusion and extension of the metacarpals to such a degree that they now resemble the raptorial arms of a mantid insect. A perfect weapon for lying in wait and surprising the small reptiles of the forest floor.

These arms and the ambush-tactics they facilitate are also all that the mantiraptor has in its favour. Despite its superficially dinosaur-like appearance, it is neither fast nor agile. Its metabolism is slow and it can spend hours, maybe even days, standing or sitting completely still, hidden behind bushes and ferns thanks to camouflage, its breaths so shallow that they do not even create visible movements in the chest. Only when some sensory stimulus occurs do the arms, fueled by a short burst of anaerobic energy, lunge forward and primal instincts kick into gear, mindlessly holding onto whatever has been caught and methodically disassembling it with the crocodilian maw. Once its belly is filled, it seeks shelter and goes to sleep for long periods until hunger strikes again. Its name may evoke associations with the smarter dromaeosaurs of the Cretaceous, but the mantiraptor’s brain is about as complex as a frog’s, if not dumber. While such a robotic being may seem easier to handle, it is exactly this mechanical mind which makes it so dangerous. Whereas smarter predators may hesitate to attack a new animal they do not know, for they may rightfully sense that something unknown may be dangerous, the mantiraptor will disassemble a human just as much as anything else that walks in front of its cold eyes.

Compared to other mantiraptor species, Olson’s mantiraptor is unique for still having a more “classic” style of reproduction. The larvae develop from waterborne eggs and go through an aquatic phase where the raptorial arms develop first in order to feed on small fish and the tadpoles of other anamniotes. Mantiraptors do not go through multiple distinct sub-adult morphs like other anamniotes on Ryl Madol. After the hindlegs evolve and the gills are reabsorbed, the young quickly leave the water and come to resemble miniature adults. More derived species, like Thylacosaurus, have shortened this life cycle even further by carrying around their eggs and larvae in a brood pouch on the back until they can walk by themselves, a method which resembles the marsupial frogs of Australia.

Moschoposeidon

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Though not big enough to stop the flow of rivers, when this beast wades through the murky waters of Ryl Madol, the other animals are sure to feel its presence. With the shoulder-height of an elephant, it is among the largest herbivores of the island.

Moschoposeidon pachyostosteus (pronounced “mos-kho-poseidon”) is a tapinocephalian therapsid that feels at home both on land and in water. In some ways it reminds one of a hippopotamus, with its bulky body and smooth skin. Also like a hippo, its feet and toes are large and broad, allowing for good grip on muddy ground. However, its long neck allows for a far greater range in diet. In water it can easily lean down and pick up various algae and aquatic plants, while on land it can reach for tall tree canopies. Its teeth are simple, mainly made for raking off vegetation and less so for chewing. Instead, the food is masticated with the use of stomach stones (gastroliths). If swallowed in great numbers, these may also help with buoyancy.

The idea that the long neck primarily evolved as a snorkel to breathe when the animal is fully submerged in deep water has proven to be incorrect. Even with the robustly built ribcage, the water-pressure at such depths would be too much for the lungs to be able to greatly expand. It is probably for this reason why these animals prefer to wade only through shallow water, with their bodies being only half-submerged.

Moschoposeidon appear to be surprisingly calm when approached by humans, but that does not mean they cannot act aggressively. Giving live birth, the females can be angered very easily if they feel any source of potential danger coming near their child. During mating season, males can also be observed fighting over access to females with necking-duels, which are simple pushing matches similar to those of elephant seals. The closely related Ceratocephalus exhibit a similar behaviour, but use ossicones growing from their heads to hit each other like giraffes.

The beasts defend themselves by using their great bulk to trample foes to death. If a predator proves to be too formidable or too large to be defeated or intimidated, Moschoposeidon will try to flee into water. Unfortunately, many of the larger carnivores descend from amphibians and so can follow them there.

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.

Armatosaurus

Parareptiles, whatever they may be cladistically (A sister-group to all other reptiles? The ancestors of turtles? A deceptively derived group of diapsids? Not even a real clade?) are abundant on Ryl Madol, though they usually descend from little-known groups that were small and lizard-like during the Paleozoic, such as procolophonids, bolosaurids, millerettids and lanthanosuchids. Except for the hylobolosaurs, most of these descendants do not differ much from their unassuming ancestors. The more famous groups, chiefly the pareiasaurs, which in the Late Permian were the largest herbivores, are rare. This is perhaps not that surprising, as large-bodied and metabolically active creatures (which pareiasaurs possibly were), are more prone to extinction and environmental change. Some scant fossil evidence suggests that, not too long ago, the landmass that would become Ryl Madol used to have its own fauna of giant-sized pareiasaurs, which in many ways convergently resembled ankylosaurs. What has led to the extinction of this megafauna is not known. Possibly, rising humidity, shrinking of the island and growth of vast rainforests reduced the natural habitat that these dryland-reptiles were adapted to and they could no longer compete with the giant diadectosaurs.

The few remaining pareiasaurs are those which have found ways to evade this competition. Some have shrunk in size and evolved unique adaptations, such as the small Neoanthodon of the lowlands, which has evolved a retractable carapace that looks (indeed very suspiciously) like that of a tortoise. But most instead retreated into habitats that are hardly accessible to the ferocious anamniotes, becoming highland-specialists. At about the size of a sheep, Armatosaurus alpinus is the largest of these.

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At first glance, Armatosaurus appears fairly unchanged compared to its ancestors. Especially the horned head bears great resemblance to the extinct genus Elginia of the Scottish sandstones. The spiky dermal armour also appears like a natural evolution of the osteoderms that were already present in the skin of older pareiasaurs such as Scutosaurus and Anthodon. The strongest change is instead found in its limbs. While some ancient pareiasaurs like Bunostegos had already experimented with rectigrade postures, Armatosaurus has taken this development to its inevitable conclusion and has its legs completely tucked underneath its body, walking much like a mammal. With a slenderer build, hooves on its front-paws and tortoise-like hooking-claws on its toes, it is thus perfectly adapted towards traversing the treacherous cliffs of the island, which often threaten to crumble at every step.

Armed with grinding teeth and gastroliths, Armatosaurus is able to feed on the few hardy plants that the barren uplands have to offer. It itself is preyed on by opportunistic mountain predators, such as giant celaenosaurs and gorgopards, but the armour and horns make this difficult. Instead of direct attacks, most hunting strategies consist of luring the prey into a trap, where a simple slip can send someone over a lethal cliff edge.

While not exactly gregarious, armatosaurs can usually tolerate others of their species in their territory, though males, especially during breeding season, can pick fights with each other. These usually consist of pushing matches, where the flat skull-roof and horns are used to force the opponent into submission. These fights can sometimes result in accidents where the defeated opponent is pushed down a slope, often to his death.