That means that they have no relationship to modern gliders, which emerged about 50 million years ago.
According to BBC News, the creatures apparently possess adaptations such as long limbs, long hand and foot fingers, and wing-like membranes that would have allowed them to climb up trees, roost in branches and glide from one tree to another - meaning that ancient mammals developed these abilities far earlier than experts previously believed.
Tens of millions of years before bats took wing, tiny mammals were gliding from tree to tree in what is now eastern China, new fossils suggest.
"Despite the fact that early mammals lived in ecosystem dominated by dinosaurs, they occupied many ecological niches", says paleontologist zhe-XI Luo from the University of Chicago, published their study in the journal "Nature".
Gliding mammals today include flying squirrels, lemurs and possums.
The ability to glide is thought to evolve so that these tree-dwelling animals can efficiently explore food sources scattered among the trees.
The wings are the preserved remains of a skin membrane that stretches, parachute-like, between fore and hind limbs, allowing the creatures to glide.
Fossils of two of the animals, Maiopatagium furculiferum and Vilevolodon diplomylos, have been discovered in China. They belong to the haramiyidans, an entirely extinct branch on the mammalian evolutionary tree, but which may have been to a forerunner to modern mammals.
"We continue to be surprised by how diverse mammalian forerunners were in both feeding and locomotor adaptations". It's likely the new fossil species benefited from gliding in similar ways.
Maiopatagium was 23 cm in length, almost the size of the flying squirrel, had the small teeth of a bat, suitable in order to gnaw the fruits and succulent stems of plants. The fossils also showed that the bones in forelimbs were proportioned similarly to the bones in other known gliders, and the shoulders were seemingly created to maximize mobility-a must-have for being able to glide through the sky on extended arms.
The two newly discovered creatures also share similar ecology with modern gliders, with some significant differences.
While most of their modern counterparts feed on the seeds and fruits of flowering plants, the Jurassic gliders lived before flowers had evolved.
But Maiopatagium and Vilevolodon lived in a Jurassic world in which the plant life was dominated by ferns and gymnosperm plants like cycads, gingkoes and conifers-long before flowering plants came to dominate in the Cretaceous Period. This distinct diet and lifestyle evolved again some 100 million years later among modern mammals, in examples of convergent evolution and ecology.
"It's fantastic that the aerial adaptions occurred so early in the history of mammals", said study co-author David Grossnickle from University of Chicago.
"Not only did these fossils show exquisite fossilisation of gliding membranes, their limb, hand and foot proportion also suggests a new gliding locomotion and behaviour", said Grossnickle.
This showed that ancestral mammals adapted to a challenging environment and tough competition from dinosaurs.
This adds to evidence that mammals were more diverse during the age of dinosaurs than previously realised. Additional authors include Qing-Jin Meng, Qiang Ji, Di Liu, Yu-Guang Zhang and April I. Neander. There appears to have been an evolutionary explosion of mammalian life styles that occurred deep in the Jurassic.