A tall, lanky figure darts across a patch of open plains somewhere in western Sub-Abeli. It turns, searching for danger, before continuing on. It has lost track of its herdmates and must now follow their scent trail in hopes of catching up before nightfall. It moves with impressive speed, placing its weight on just two toes per foot. This is an adaptation for efficient running, a feature that allows it to track its family well into the evening. Its tail streams behind it; occasionally, it flicks a fly away using the tuft of fur at the end. As it closes in on the other rats, it sees that the seeds have been chewed off the local rat-grasses. This is its species' primary diet, for there is little nutrition in the dry, half-dead leaves and stems. As the light fades from the sky, it slinks into the patch of grass the herd has flattened to sleep in. A few members keep watch; the formerly lost individual trots up to greet one. It joins the sentries, unable to sleep because of the adrenaline that still hasn't left its system. In an hour or so, it will finally get some rest as the next shift awakes to protect the group
This social and adaptable rat is a Rattalope (Peragrattus subabeliensis), a Rattus migratorius descendant. Its genus contains a handful of other species, all collectively known as Muridiungulates. Already their claws are becoming thicker and load-bearing, the first step towards evolving true hooves. Their molars are large and strong, pulverizing the tough rat-grass seeds that compose over 90% of their diet. The incisors, on the other hand, are slow-growing and rather thin; their only purpose is to gently clip grain-bearing stalks from their mother plants.
This species is the largest in its genus, weighing up to fifteen kilograms. Rattalopes and other Muridiungulates have well-developed pups, which can stand, run, and begin drinking milk just moments after birth. They won't be weaned for up to six months, as their post-birth growth is much slower. This necessitates the protection of the herd, members of which take turns keeping a lookout for the benefit of all. If a predator approaches, an alarm will be sounded. Once the herd is alerted, though, it's every rat for themselves. Rattalopes need not outrun their predators; they need only outrun the slowest of their herd. Mothers alone put any effort into protecting their young, and they may stand their ground if they think they can fend off a foe.
Herds of Peragrattus are quite fluid; if the young female from earlier had stumbled upon a different group of conspecifics, they would've accepted her as their own. Males, though, have a more difficult time. While several may be present in a single herd, dominance hierarchies are strict and newcomers will automatically begin at the bottom (if the dominant individuals accept them at all). Once weaned, young males are driven out by their fathers, while their sisters remain with the herd of their birth. This prevents inbreeding and allows successful males to ensure their sons will spread their genes far and wide.
As the largest and most common herbivores on the rat-grassland, Muridiungulates like P. subabeliensis are the foundation of more complex food chains. Their predators - ratweasels, for example - find success wherever this group is present. In their migrations, members of this genus disperse their food source over vast distances, in addition to fertilizing the grassland with their manure. The overall result of their presence is a productive but homogeneous habitat, one where a few rat-grass genera dominate to the exclusion of all other plants.