Tepuine herd-birds first re-entered Apterra's global ecosystem at the height of the Ice Age, becoming a staple of prairie ecosystems by the time the Arthrocene began. As generalist herbivores, they weathered the floral shifts from woodlouse-grassland to loop-grassland to the basket-grassland of today. Their descendants - known as Steppesteppers (Polyovapteryx) continue to roam the open plains of Ailuropia, where they are the most numerous medium herbivores. Here they live alongside quarter-ton Delta Beakbucks (Latirostravis deltaensis), which can eat nearly all forms of vegetation, and the pickier Barrelbuck (Doliopascus deltaensis), a species of small basketbuck Muridiungulate.
Steppesteppers are of moderate size, weighing on average seventy kilograms, and are the fastest runners on Apterra, reaching up to 75 kilometers per hour in a sprint. Such speed is possible because their long tails serve as anchoring points for massive leg muscles. Steppestepper tails also provide a counterbalance, allowing the genus to evolve a larger torso that houses a spacious pair of lungs, granting them impressive endurance; they can maintain a velocity of 45 km/h for over thirty minutes with ease.
In terms of diet, steppesteppers are intermediate between the picky barrelbucks and the indiscriminate beakbucks. Though they prefer the sweet, nutritious shoots of sodstalks, jade skystalks, and other woodlouse-grasses, they supplement their meals with soft plant matter of all varieties. They often follow behind beakbuck herds, as the kiwizelles tend to destroy tougher vegetation. A few days later, the normally rough plants sprout again, allowing the steppesteppers to take advantage of the soft new growth. Polyovapeteryx are also not opposed to eating small amounts of meat; though they rarely actively hunt, they sometimes feed opportunistically on carrion or small, helpless rodents and birds. This is especially true of young steppesteppers, which must grow quickly to avoid their own predators. Chicks commonly go after large castlebugs, dustflies, newborn swattermice, and other slow-moving targets.
Steppestepper reproduction is another feature highly unique to this genus. During their long exile on Tepui Mons, there were few threats to their ancestors' nests. As a result, Acrapteryx evolved to lay quite small eggs compared to most kiwi species, with chicks hatching at only around half a kilogram in weight. Once they arrived in the lowlands, however, they found that their young were being picked off in large numbers, limiting the growth of the species. The proto-steppesteppers quickly adapted to lay multiple eggs in a row, a trait shared by no other Apterran bird. Today, steppestepper females can incubate up to six offspring in each clutch, greatly increasing the odds that at least one or two will survive to adulthood.
Some species of steppestepper have retained the close-knit herd mentality of the tepuine herd-birds, living in large nomadic groups. For example, the Eastern Stepppestepper (P. praetermons), which lives on a small strip of grassland on the Medithalassic shoreward side of the southern Ailuropian mountains, comprises a single, 50,000-strong herd that wanders the entire territory together. Another gregarious variety is the Greater Steppestepper (P. vagaris), which ranges across all the temperate regions of the Deltalands. Its herds rarely exceed a thousand individuals, though many groups may temporarily merge during river crossings and other dangerous passages. One species, the Straightbilled Steppestepper (P. murivora), is much more solitary, forming no long-term bonds outside of mated pairs. It is the most carnivorous of the group, sometimes going as far as to dig up burrowing rat nests to reach the families of helpless rodents within.