Rattalope Muridiungulates limped into the dawn of the Arthrocene, survived solely by their largest and most specialized member, the rattalox. Though this species did well for itself when ice dominated the landscape, it entered a decline as soon as warmth returned, finding itself restricted to small pockets of mountainous terrain where its preferred climate still existed. This quickly caused many species and subspecies to evolve through genetic drift in their isolation, but most of these lasted just a few thousand years before succumbing to inbreeding depression. Only one population, safe on the chilly and expansive Northern Isle, made it more than a million years into the current epoch. This species, the Polar Rattalox (Peragrattus relicticus), became the ancestor to all current rattalopes, some of which managed to migrate back to Panapterra before the land-bridge connecting it to the Isle sank beneath the waves.
The only member of the clade (which is now its own genus, Ungulorattus) larger than its Muricene ancestor is the Sylvilox (U. borealis). Averaging 350 kilograms in weight, this species faces no natural predators as it grazes and browses the lowland woods and meadows of the Isle. Its size often gives it trouble when moving through dense forests, as giant hybrid trees tend to pack tightly together, supported by the heavy rainfall the Isle gets throughout most of the year. Though the sylvilox is among the largest mammals on the planet, it's still not big enough to fell these palm-grasses on its own. To clear a path, the entire herd of 20 or more must work together, pushing the trees to the ground and feeding on the rich and now easily accessible foliage of their canopies. In this way, not only do the sylviloxen gain access to an otherwise out-of-reach food source, but they also create easy escape routes for their calves, which are not nearly as invulnerable to predation as the adults.
Most other rattalox descendants have gone down a very different path, decreasing in size and becoming more generalistic in order to claim new niches. For example, the Mazamox (U. cervoides) lives on the slopes of the Isle's many mountains, feeding on shrubs, bryophytes, lichens, spiny-grasses, and anything else it can find. This is the habitat that most closely resembles the environment the original rattalox called home, but this small species (no more than 75 kilos) is more nimble and can survive on less food, so it finds more success here than its larger congenerics. In exchange, it must contend with the fearsome Island Grimbill (Ursapteryx insularis), a sure-footed opportunist that's happy to snatch a mazamox away from its herd whenever it gets the chance. It employs a modified version of the typical grimbill technique, with one partner scaring the rattaloxen into fleeing downhill, trying its best to chase them in a specific direction. The Muridiungulates soon find themselves facing the other hunter as it emerges from some hiding place along the path. At this point, the herd's only defense is to keep charging forward, hoping to either scare away the grimbill or plow straight through it at full speed. Once they commit to the stampede, there's no turning back; if one of the mazamoxen hesitates, it will be left behind by its fleeing herdmates and fall directly into the jaws of the hungry kiwizelle pair.
Only one rattalox lineage made it back to the Panapterran supercontinent before the connection between Loxodia and the Northern Isle disappeared forever. This group led to the modern Impalox (U. aepycerotoides), a savanna-dwelling species that ranges across the interiors of Loxodia and Abeli. Roughly the same mass as its mazamox cousin, this fast-running prey animal has a lankier build, with longer, more muscular legs and a neck that's held almost horizontally when at rest. Jutting out from just behind its eyes is a pair of ossicones, supported by a bony core and covered in a thin layer of skin and fuzzy yellow hair. These have little use against predators, as they don't possess a sharp keratinous sheath and can't withstand blunt-force impacts, but they are helpful for intraspecific displays. They are an all-purpose communication tool - calves can find their mothers by searching for the tufts of yellow sticking out above the tall grass, while males can avoid violence by showing off the size of their ossicones to each other and to onlooking females. This allows impaloxen to live in close-knit social groups without violent competition, which in turn reduces their losses to predators.