Avimanders of the Hothouse

The closest living relatives of the widely-diverse skuorc clade are much harder to see in the landscape. With few exceptions, they are small, cryptic animals, strongly associated with water. The avimanders survived into the hothouse with a single representative genus, the stream-dwelling riverrunners. Alongside the skuorcs, they are the only other living ornimorph birds, and just like skuorcs, their development has become permanently halted at an early developmental stage, with the genes that once produced the flying adult life stage now fully lost to time. Avimanders resemble newts and salamanders; they have smooth skin through which most species can absorb oxygen, four legs (though the front ones have only a single digit, and are more useful to clamber on the substrate underwater than to bear weight on land), and a cartilaginous paddle-shaped tail for propulsion. The ear is reduced to an exposed eardrum, as in frogs, but remains useful to pick up noises underwater. The jaws are robust, with a beak only at their distal tip; very fine keratin serrations function as teeth to hold and restrain small animal prey - most, but not all, species are predatory.

Ten million years into the hothouse, the small and inconspicuous riverrunner has speciated into different forms, filling new niches in a widened, wet world. These animals out of all all their ice age relatives survived because of their incredible cold hardiness and reliance on freshwater, rather than the sea, for the latter suffered a mass extinction during the great thaw while the former remained clean and abundant due to glacial runoff. Two species of hothouse riverrunner are seen above, one which has become a more aggressive carnivore, and one which has become an aberrant herbivore, among the first avimanders to vary their diet in such a way.

The 10 inch long streamspear is a primitive riverrunner, which still dwells in flowing freshwater. Its skin appears hairy at close inspection, for it is covered in a fine layer of short, fur-like threads of skin which increase its surface area for respiration. A denizen of swiftly flowing and thus well-oxygenated water, the streamspear's lung is nearly useless, and it can breathe without ever surfacing for atmospheric oxygen. Streamspears clamber over and under rocks with their long grasping toes and hooked forelegs, looking for the perfect hiding place to cling out of the current and lie in wait for prey, such as small fish, to pass by. Its eyes are massive and so its eyesight excellent. It watches and waits, tracking any small movement which could mean an approaching  meal. Then, in an instant, the streamspear launches its front legs out and up at a target, skewering it as if with a lance, and then pulling it down into its rock crevice to feed.

The 20 inch long duckbilled saladmander, in contrast to its relative, is a harmless, slow-moving avimander of stagnant, warm freshwater such as is common in the soglands. This very different environment has produced more substantial changes in this animal, which has a reduced covering of "hair" and a very large lung so it can gulp air from the surface, as its habitat (and its relatively large size) doesn't provide enough oxygen to sustain it from skin respiration alone. Without flowing water to bring food its way, the saladmander has also remained a more active forager. Its ancestors mostly picked small invertebrates from rocks, crawling along in search of food. The saladmanders do still eat some invertebrates, but have evolved to feed in a less selective way by scraping hair-like algae growth from surfaces with a finely serrated, flat, duck-like bill and so collect both the plant and any small morsels hiding within it, all of which it can digest. Because much of their diet is vegetable, and thus virtually unlimited duckbilled salamanders can become very numerous in the soglands and are an important food source for many other birds and tribbetheres.

All riverrunner avimanders spawn in water and lay eggs which are fertilized externally. River-dwelling species like the streamspear are effectively broadcast spawners, and their eggs flow downstream and eventually settle in rock crevices. Saladmanders, in contrast, deposit their eggs in clusters on underwater vegetation. Both species have larvae which are carnivorous and feed largely on small crustaceans and tiny insects in their first few weeks; those of the streamspear cling on the underside of rocks to avoid being swept away, while saladmander larvae are free-swimming and form schools that wiggle around just above the sediment, collecting small food particles. As these larvae grow larger, they gradually become benthic and start to crawl around with their legs, only swimming in short bouts to reach the surface to breathe or to flee a predator. The diet switches to a mostly plant-based menu when the larvae are around six inches in length; before this time, their gut is too short to efficiently digest it.