In a world filled with dinosaurs, the skies are as fantastical a place as the land. Your garden variety birds, as varied and colorful as they are in our timeline, are joined by more ancient creatures, birds with claws and teeth, and some with long tails. The pterosaurs, greatest of all vertebrate fliers, are also present, some reaching the size of airplanes. Amidst all this diversity, it’s perhaps surprising that a group of mammals also managed to take to the air, no less diverse then the bats of our timeline. But these are not bats, even a cursory glance at one at rest will confirm this. Their wings are made from two fingers, not four, and are covered in a layer of fine hairs. On the ground they walk similarly to pterosaurs, as quadrupeds with their wings folded up. They often retain long bushy tails. And their faces are distinctly squirrel-like, with big, beady eyes, and gnawing teeth. These are the wingrats, most successful of all the multituberculates.

Multituberculates are an ancient lineage, first appearing in the fossil record more then 150 million years ago. _. In our timeline they went extinct at the end of the Eocene (with the exception of a few stragglers in the southern hemisphere, which survived into the Miocene), perhaps due to competition with true rodents. But there are no rodents in this timeline, and multituberculates continue to thrive all over the globe. Their greatest success story begins in Asia during the Late Eocene. As the climate began to cool, and tropical rainforests were suplanted by more open woodland, some arboreal cimolodonts began to experiment with this new habitat. Better climbers then they were walkers, they were quite vulnerable on the ground. As the trees increasingly spread apart, and grass began to take over, a new strategy for avoiding predators was needed. It was this need that spurred on the evolution of the wingrats, which rapidly diversified in Asia. No longer restrained by natural boundries, the group spread to every major landmass in just a few million years.

Being such a diverse group of animals, wingrats fill a wide variety of niches. Specialists of fruit, insects, small vertebrates, and even nectar exist. But the ancesteral form was a granivore, and the majority of species keep to this lifestyle. This major difference from bats (which are primarily insectivorous) has had ripple effects on the evolution of other flying vertebrates. Nocturnal, insect-eating birds are significantly more diverse in this timeline, while seed-eating passerine like birds are significantly less so. Combining some of the best traits of both bats and rodents, wingrats are the most diverse order of mammal in this timeline, with over 1300 species. Most are quite small, an ounce when soaking wet, and even the largest species has a wingspan no longer then 6 feet. They have a global distribution, absent only from Antarctica. Their fluffy wings means they are more comfortable in cold weather then bats are. They lack the ability to echolocate, navigating the world primarily through their excellent senses of sight and smell.

Wingrats can be divided into two major groups. The first (which is polyphyletic), remains clumsy on the ground, and therefore tends to rest in trees, caves, or on clifffaces. Curved claws on the three wingless digits allow them to effortlessly cling to vertical surfaces.In many arboreal species, one of the wingless digits has become a sort of prehensile psuedo-thumb, which allows them to clamber through the trees with ease. (One more sentence on “primitive” wingrats). The second group