In dense Chinese forests populated by dinosaurs 160 million years ago, two furry critters resembling flying squirrels glided from tree to tree, showing that even in such a perilous neighbourhood early mammals had succeeded in going airborne.
Scientists on Wednesday announced the discovery of fossils of two Jurassic Period gliding mammals so well preserved and complete they show the wing-like skin membranes the creatures employed while gliding effortlessly between trees.
The species, Maiopatagium furculiferum from Liaoning Province and Vilevolodon diplomylos unearthed about 65km away in Hebei Province, come from an extinct early mammalian side branch.
These two and another apparent glider from about the same time that was described in 2006 were the vanguard of the mammalian air force.
It was not until more than 100 million years later that bats, which use powered flight like birds, and more gliding mammals appeared, following the dinosaurs' demise.
Mammals first appeared about 210 million years ago.
These fossils underscore that early mammals were not merely cowering at the feet of dinosaurs but boasted a range of body plans and lifestyles.
"Despite living in dinosaur-dominated ecosystems, early mammals diversified into many ecological niches," said University of Chicago paleontologist Zhe-Xi Luo, who led the research published in the journal Nature.
The new species were unrelated to today's four groups of gliding mammals: flying squirrels in North America and Asia, Africa's scaly-tailed gliders, Australia's marsupial sugar gliders and Southeast Asia's colugos.
Maiopatagium was about 23cm long, similar in size to flying squirrels. Vilevolodon was a bit smaller.
Maiopatagium's teeth resemble those of fruit bats, suggesting it ate soft plant parts, while Vilevolodon's teeth were more like those of squirrels and good for eating seeds.
They lived at a time when small feathered dinosaurs such as Anchiornis were also experimenting with flying, on the evolutionary road leading to birds.
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