It's A Bird. It's A Plane. It's A Jurassic Mammal!

Barsaba Taglieri
Agosto 10, 2017

Two 160 million-year-old mammal fossils discovered in China show that the forerunners of mammals in the Jurassic Period evolved to glide and live in trees.

But now scientists say there were also gliders - early relatives of mammals, akin to today's flying squirrels - whizzing through the trees.

The smaller of the two, Vilevolodon diplomylos, is three inches long, and its fossil is also preserved with a skin membrane "as if it's a museum-prepared specimen", he adds. The fossils are described in two papers published this week in Nature by an global team of scientists from the University of Chicago and Beijing Museum of Natural History.

The fossils were discovered in the Tiaojishan Formation to the north-east of Beijing.

"These Jurassic mammals are truly 'the first in glide, '" said Zhe-Xi Luo, professor of organismal biology and anatomy at the University of Chicago and an author on both papers.

The fossil record for the forerunners of mammals in the Jurassic period has been poor, Luo said, "so we have this biased impression that early mammals are not terribly diverse, not terribly interesting because they are dominated by dinosaurs". Both of the mammals - named Maiopatagium and Vilevolodon - belonged to the long-extinct haramiyidans group.

The ability to glide between trees allowed the ancient animals to find food that was inaccessible to other land animals. Both fossils show the exquisitely fossilized, wing-like skin membranes between their front and back limbs.

This is evidence of convergent evolution, he says - or the ability of animals to independently evolve the same feature if it offers them an advantage.

While most of their modern counterparts feed on the seeds and fruits of flowering plants, the Jurassic gliders lived before flowers had evolved.

The ancient mammals' way of life was associated with feeding on entirely different plants, namely cycads, gingkoes and conifers. 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.

"It's unbelievable that the aerial adaptions occurred so early in the history of mammals", said David Grossnickle of the University of Chicago, author of a study in the journal Nature on the findings, in a statement. "Not only did these fossils show exquisite fossilization of gliding membranes, their limb, hand and foot proportion also suggests a new gliding locomotion and behavior".

The discovery of the two fossils shows that early mammals were highly diverse despite living in the shadow of the dinosaurs.

"These new fossil gliders are the first winged mammals, and they demonstrate that early mammals did indeed have a wide range of ecological diversity, which means dinosaurs likely did not dominate the Mesozoic landscape as much as previously thought", said Luo.

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