Basilosuchus

Click to enlarge

Huge, ferocious and carnivorous, Basilosuchus imperiosus, though rare in its adult form, is a creature feared across the whole island. Here we see it, among the ruins, feeding on a dead Megarhinosaurus, a poor dinocephalian that was probably slain by the giant predator.

Basilosuchus is a bipedal creature, often walking with a horizontally held spine, with prominent armour plates along the back. Its tail ends in a flattened paddle, painted with a prominent spot probably used for social signalling. The three horns on the skull may also serve a similar purpose, though they might also be used for interspecies territorial fights.

Click to enlarge. Life stages are not to scale.

The most fascinating aspect about this creature is its life cycle. Despite appearances, Basilosuchus is not a dinosaur nor even a true reptile. It is an “anamniote”, a reptiliomorph stegocephalian, more closely related to us than to true amphibians, but still outside the Amniota. As such, while it has many reptilian characteristics, it still lays its eggs in water, where they hatch into tiny, gill-bearing tadpoles. While it seems archaic, this has allowed Basilosuchus and many other Rylian anamniotes to evolve a complex life cycle which prevents the juveniles from competing for the same limited resources of the island as the adults.

After the tadpole loses its gills and grows its hindlegs, it turns into a large amphibian with simple armour-plates along the back. This stage strongly resembles creatures from the fossil record known as Chroniosuchia, which may show where the origins of Basilosuchus lie. This stage lives as a crocodile-like ambush-predator in swamps and rivers.

After some time, the hindlegs of the chroniosuchoid grow longer and the limbs are tucked underneath the body. The jaw becomes more crooked and horns start growing on the snout. This new “suchoid” stage leaves the water and starts living inland, especially the cluttered rainforest, where it preys on smaller animals. This stage is morphologically and ecologically perhaps most comparable to one of the extinct land-crocodilians.

With time, the “suchoid” increases in size, the hindlegs become longer, more robust, and it starts walking on them more and more until it becomes fully bipedal and ventures into the open forest galleries and fern prairies. This is generally where adult life begins. But, fascinatingly, depending on environmental conditions, both the chroniosuchoid and suchoid stages can already become reproductively active, at which point they actually remain in this stage for the rest of their life. “Juvenile” Basilosuchus are thus encountered far more often than the ferocious adults and take on their own specific roles in the ecosystems they inhabit.