Monday 5 February 2024

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.

Sunday 4 February 2024

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.

Click to enlarge.

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.

Sunday 28 January 2024

Aistoconstrictor

Click to enlarge.

There are no snakes on Ryl Madol. In their stead slither other, more ancient creatures through the underbrush. Most numerous among these legless vertebrates are aistopods, an ancient lineage of stegocephalians. These were the very first tetrapods to completely lose all of their limbs and in these primeval jungles they have further converged on the serpents that replaced them elsewhere in the world.

Largest among them is Aistoconstrictor latagnathus, which, it has been reported, can grow up to nine or ten metres long, larger than any anaconda. Most individuals are smaller though, usually maxing out at around six or seven metres. Despite technically being an amphibian (in the classic paraphyletic sense), Aistoconstrictor shares many characteristics with actual constricting snakes, such as boas. It kills and captures small prey, such as lystrodos, by biting their head and then ensnaring them with its body, crushing the poor victim under its weight.

Click to enlarge.

Looking at the skull we can see a combination of both old and new. Overall, the cranium still bears great resemblance to ancient aistopods such as Phlegethontia, with large orbits, large fenestrae and a light construction at the back of the skull that gives the jaw-joints a larger range of movement. Differing from ancient aistopods, the “aistoboids” evolved an extra jaw-joint in their lower jaw, allowing the dentary to articulate with the surangular bone. Like in constricting snakes this allows the predators to “shove” prey down its gullet with its teeth by moving the lower jaw back and forth. Unlike in snakes, the mandibles are still connected at the tips, so they cannot open as widely.

Click to enlarge. Life stages are not drawn to scale.

Being a stegocephalian, likely of the reptiliomorph variety, Aistoconstrictor develops from an aquatic larval stage. It does not raise its young on land in burrows like a giant caecilian, as older textbooks have often wrongly stated. After internal fertilization, the eggs are instead laid into a breeding pond, which the mother often guards until hatching, as some toads are known to do. Upon hatching, the larvae emerge as little eel-like creatures with surprisingly long external gills. At this stage they bear a great resemblance to the larvae of caecilians, though this is surely a coincidence. These aistoboid larvae feed on aquatic insects and algal scum before they grow in size and enter the next life stage, the “spade eel”, named after the shape of its snout. Its gills have shrunk and become covered by a soft skin-flap, while its swim-bladder has expanded into a simple lung, allowing it to breathe both in and out of water. The spade eel lives much like a predatory fish, feeding on many smaller vertebrates by use of ambush attacks. They are also surprisingly gregarious, often swimming in small swarms for protection. Unlike the sub-adult stages of some other Rylian reptiliomorphs, spade eels cannot become reproductively active and are always destined to grow into fully adult “aistoboids” once they lose their gills and live on land.

As a human can in some ways resemble other bipedal animals on Ryl Madol like the lystrodos or avibolosaurs, it may not come as a surprise that stalkers and other explorers are frequently attacked by Aistoconstrictor and relatives, whose coloration conceals it behind the underbrush or lianas. While the creatures are capable of killing people through constriction, human shoulders are usually too wide to fit through the jaws, so the beasts tend to give up after the head and just leave behind a mangled corpse for the scavengers.

Thursday 18 January 2024

Marine Centipedes

Myriapods have a long history, stretching all the way back into the Palaeozoic, though they would not become truly successful until the Age of Dinosaurs. That success seems to have been repeated on Ryl Madol, attested to by the island’s diverse fauna of millipedes and centipedes found nowhere else on Earth.

Among these are the marine centipedes, Platychilopodidae, which inhabit the waters surrounding the island. Living their whole lives at sea, their bodies have become streamlined, their legs became flattened flippers and their caudal legs form something that could be called a tail fluke. They even evolved so-called blood lungs inside their tracheae, a trait otherwise only known from aquatic insect larvae.

Chilocaris venefecus is one member of this family. Its preferred prey are other arthropods and small agnathan fish, such as neothelodonts, which it captures with its large jaws and injects with venom. It itself is preyed on by large fish and marine reptiles and amphibians. As many would-be explorers have painfully found out, if the “marinopede” cannot defend itself with its venom, it will use its “tail-fluke” as a pincer.

Among the Platychilopodidae, C. venefecus is one of the smaller species, growing about 20 centimetres long. It is far outdone by the horrifically large Con Rit, Cetioscolopendra aeliani.

Sunday 14 January 2024

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.

Friday 12 January 2024

Arachnosaurus

While giant spiders are unknown here, arachnophobes are still not safe on Ryl Madol. High up in the canopy lurks a creature appropriately christened Arachnosaurus nychuros. Its prehensile tail makes up over half the body length and is used to lower the animal head-down into the air like a lantern.  The arms and legs are strong and built for climbing, like a chameleon's. The hindlegs are relatively short and tucked close to the body, but the toes are disturbingly long, splayed and tipped with curved claws. Cryptically camouflaged among the vines, Arachnosaurus hangs in wait for hours with its feet stretched out waiting for prey. This may include insects even smaller flying reptiles that happen to fly through the jungle, though the predator also seems to be content with arthropods and “lizards” that happen to waddle a few tree-branches below. Once in reach, Arachnosaurus envelops its prey in a deadly hug it cannot escape from and uses its pointy mouth to feed on it while it is still alive. After the first few bites the prey-animals seem like they are paralyzed, suggesting the use of some type of venom, but autopsies have so far been unable to find venom glands in Arachnosaurus, making this rather mysterious.

Arachnosaurus are surprisingly gregarious, often hanging from the trees in medium-sized groups like bats do, though they do not cooperate when it comes to hunting or fending off predators. They make no audible sounds and instead seem to communicate by changing the color of their headcrest.  Mating usually entails the male presenting the female with a gift in the form of food. After mating, the female builds a nest in a hollowed-out tree-hole and lays its eggs there. The mother guards the nest and even leaves some food behind shortly before the eggs hatch, but once the young emerge they are left to themselves. 

Unlike the anamniotes of the forest floor, Arachnosaurus is a true reptile that lays hard-shelled eggs, though its exact affinity remains uncertain. It appears to descend from some group of basal diapsids, perhaps Araeoscelidia similar to ancient Araeoscelis and Petrolacosaurus.