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.

Gorgoraptor

 Although true dinosaurs are sadly absent from Ryl Madol, many similar-looking creatures have convergently evolved in their stead. Among them are the lycaenoraptors, of which Gorgoraptor pilosus is a member. Though bipedal and digitgrade like theropods, the saberteeth and faint hairs along the back show that these are in fact some kind of therapsid, descending from the likes of gorgonopsians, therocephalians or perhaps even cynodonts. 

Using their great sense of smell and decent eyesight, these small-to-medium-sized predators opportunistically stalk the meadows and forests in search of prey. While its smaller relatives live in packs, Gorgoraptor often hunts alone. When it captures prey like lystrodos, it pins them down with its powerful legs and arms and deals the killing blow by severing their windpipe with its characteristic saberteeth. It itself can fall prey to the much larger Carptophoneus, the anteosaurid(?) "tiger" of the island, and of course the titanic Basilosuchus and Decarnodon, anamniote reptiliomorphs, the latter of which could give even large theropods like T. rex a run for their money.

As, unlike true mammals, these synapsids still have full colour-vision like other amniotes, they can often be found with striking patterns and colour schemes. Apart from charismatic stripes, the mane along the neck and back can also shine in bright colours. Perhaps, long ago in the distant past, this is how hair first got its start, not as a means of insulation but as a display feature.

Didontornis

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In the horsetail meadows of Ryl Madol, a strange fellow can be encountered, A biped, both feather- and furless. But, contra Plato, it is not man, nor even really mammal. Although now heavily altered and resembling more a naked, flightless bird than anything else, the two small tusks growing behind the beak still give away the true ancestry of this Paleozoic survivor. It is a dicynodont therapsid which has learned to walk on two almost humanoid legs. With these, as well as its horizontal pupils, it is well-equipped to evade the predators which may lurk among the tall seed-fern-flora. Yet, these little herbivores still tend to fall prey to the likes of lycaenoraptors and aistoboids.

Didontornis is a small browser that feeds on horsetails and other shrubby plants. These are cut off with the sharp beak and grinded up in the stomach using gastroliths. Only males have the distinctive tusks, which made classification of this species initially difficult when the first encountered specimens were females. The tusks probably serve as either a weapon or display feature during fights for mating-rights. The arms and legs are short and small and rarely used during foraging. When two didontornes get into a scuffle, they sometimes try to slap each other, which can look adorable.

Didontornis is just one member of a wider group of bipedal dicynodonts, the Diornithodonta, which on Ryl Madol have taken over a similar ecological role as ground birds and fowl would do elsewhere in the world. Their common name is “lystrodos”, a portmanteau of Lystrosaurus and dodo.