Strixales: the Sharkbirds

Eargills are fully-aquatic changelings, most of which long ago lost their adult flying stages and became fully aquatic, neotenous adults. Evolution has shaped these strangest of birds strongly into the few body shapes which are efficient underwater, lending most free-swimming species (particularly in the ocean) to strongly resemble fishes, with fluked tails and even dorsal fins. Breathing through what was once the ear canal of their terrestrial ancestor, this structure has evolved into a gill on either side of the skull, which takes in water from the mouth and ejects it out the side of the head.

Despite their wildly derived lifestyles, eargills are more recognizable as birds than many other metamorph birds as their skull anatomy, outside the gill, is relatively primitive. Eargills retain beaks, though in the most successful and modern representatives these have evolved to be more like those of merganser ducks than of canaries, being covered in a hard nail-like tissue and lined with tooth-like lamellae made of keratin, similar to the ancestral structure of the viva's pseudoteeth. This gives them a firm grip upon wriggly, slippery prey: both fish and other, smaller metamorphs.

In the ocean one group of large, actively predatory eargills is especially notable. These species have very broadly evolved to fill the niches of sharks, ranging from quite modest lengths of under three feet to twenty-five feet in length. They are usually fast, with highly streamlined bodies and large tail fins (though some species are sedentary and lurk along the sea floor.) Because they usually rely on speed to catch prey and live in sunny, surface waters, they are often brightly colored. Known as strixales, or their more straightforward English translation: sharkbirds, they are a widespread and specious predator grade across the seas in the middle Ultimocene. Unlike many other bird groups of this time they are not considered highly intelligent; their brains are highly simple compared to land birds as a result of retaining a juvenile, larval-like form throughout life. But they have extremely strong eyesight designed to track motion and a powerful sense of smell, as well as a strong sense of navigation that allows many larger species to cruise the open ocean and hone-in on food, be it carrion or an injured animal.

Many strixales use their toothy jaws to rip chunks of flesh from larger animals, but others are more specialized toward small prey. Few are likely more so than the itamae (a Japanese term that can be translated as "skilled sushi chef"), a large, swift pelagic hunter that earns its name from its skillful ability to slice and dice fish with its remarkable jaws.

The Itamae is a large, blue-hued sharkbird that can grow more than 15 feet long, up to one-fourth of this length being its highly elongated beak. Like extinct swordsharks used their tails, this extremely fast-swimming oceanic hunter patrols open water, following shoals of baitfish, and uses its sword-shaped mouth to swish through them, frequently cutting them right in half. This animal has a unique kinesis in its skull that allows it to separate the two halves of both lower and upper jaws at their distal tips, turning the serrated teeth outwards so that they function like filleting knives as the hunter swiftly shakes its head side to side into a school of fish. A few sweeps through and up to a dozen mortally wounded fish are often left struggling in the water, which the itamae quickly gulps down before the blood attracts the attention of hungry relatives.

Some of the most unusual sharkbirds, though, are those which have abandoned their active pelagic niches for more benthic lifestyles along the sea sediment. Unlike their relatives these animals are often colored cryptically in order to hide, and rely on ambush instead of speed to capture prey. The highly elongated, almost eel-like sandslinkers are the most extreme examples. These relatively small strixales are immediately recognizable for their massive spiked "teeth" formed by a keratin growth over bony projections of the jaw, as well as by unusually long and sinuous necks than other species that have to be more hydrodynamic. In fact most aquatic metamorph birds, though few show it, retain many neck vertebrae and thus have considerably more neck flexibility than similar teleost fishes.

Sandslinkers spend most of their lives buried up to their necks in the sediment, often with only their eyes and their beaks exposed. Many species use their small, pink tongues as a lure - they resemble fish or small worms along the sand and attract the attention of prey which is then rapidly skewered in the pronged jaws, which close shut like a bear trap upon the slightest provocation.

Sharkbird reproduction is more or less typical for eargilled birds, involving the broadcasting of sperm and eggs into the water with no further attention paid to them by either parent. They are planktonic for the first few months of their lives, with only a small percentage growing to maturity. Older juveniles hide in vegetation until large and fast enough to begin hunting in open water (or, for those such as sandslinkers, along the substrate.) Many species show rather dramatic changes in body shape and color as they mature, reflecting movement through different ecological niches.