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.