Divergence

Since their appearance, ducktails have started to occupy the most unusual niches for a bird, but only recently two clades had started a strong divergence toward unique body plans.

The first one is the tower ducktail (Cephalaltus caudatum) or simply tower, the third-largest land vertebrate of Antarctica. Unlike bullducks, which mainly changed bone proportion to attain a large size, this anatid has drastically changed its skeletal composition. Like swifts, tower ducktails possess 4 upwards digits (pamprodactyl condition) to better discharge their weight and, like moa, they completely lack wings. Cervical vertebrae have also increased, from 16 (like most ducks) to 25 (more than a goose). This adaptation drastically improves neck mobility enhancing the possibility to snake it between branches in search of fresh buds. Large individuals can reach food up to 4 meters (13 feet) above the ground, indirectly reducing interspecific competition with sympatric species, like mastodon bullducks. As expected, tower ducktails are forest-dwellers, but small populations can be found in sub-optimal habitats, like edges of the Scrubring, riparian areas of steppe and steep woodlands. As for any large vertebrate, predation is not a limiting factor, but food availability. Tower ducktails are even well-armed against predators, with pointed horn structures over their feet that are used similarly to a nailed club, an effective defense against both herdstalkers and geotters.

While towers have deeply changed skeletally, another species of ducktail has significantly changed ecologically. We're talking about the fearsome terror drum (Carnodon silvestris), the only carnivorous member of Pygostylidae. Its smaller ancestor probably started to move its attention towards small prey like insects and bird eggs. False teeth and rough tongues are surely useful to chew and grind plants, but it was only a matter of time before some species started to use them for grasping and cutting living animals. In a few million years,  terror drums have doubled their size, being large enough to bring down medium-sized flightless birds, like rails and ground tyrants, but also small geotters or young ducktails, occupying a mesocarnivore niche. They mostly live in closed and open woodlands, where they can easily ambush their prey (despite being discrete runners).
Unlike herdstalkers, which kill by pecking in vital areas, the terror drum fatally bites their prey with their beak, thanks to their strong muscular jaws, which allow them to produce a bite force comparable to a wolf. Clawed feet are also an important weapon, being used to block small vertebrates.
Terror drums are also merciless: it's not rare that they start eating while their lunch is alive, causing a slow and painful death that nobody would wish on their worst enemy.