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First winged mam­mals from the Juras­sic period discovered

pub­lished 12 August 2017 | mod­i­fied 12 August 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. With long limbs, long hand and foot fin­gers, and wing-​like mem­branes for tree-​to-​tree glid­ing, Maiopatag­ium fur­culiferum and Vilevolodon diplomy­los are the old­est known glid­ers in the long his­tory of early mammals.

Maiopatagium, a gliding mammaliaformMaiopatag­ium in Juras­sic for­est in cre­pus­cu­lar (dawn and dusk) light: A mother with a baby in sus­pend­ing roost­ing pos­ture, climb­ing on tree trunk, and in glid­ing.
Image credit: Uni­ver­sity of Chicago; Recon­struc­tion by April I. Neander.

The new dis­cov­er­ies sug­gest that the volant, or fly­ing, way of life evolved among mam­malian ances­tors 100 mil­lion years ear­lier than the first mod­ern mam­mal fliers. The fos­sils are described in two papers, both pub­lished on 9 August in Nature by an inter­na­tional team of sci­en­tists from the Uni­ver­sity of Chicago and Bei­jing Museum of Nat­ural History.

These Juras­sic mam­mals are truly ‘the first in glide,’” said Zhe-​Xi Luo, an author on both papers. “In a way, they got the first wings among all mammals.”

With every new mam­mal fos­sil from the Age of Dinosaurs, we con­tinue to be sur­prised by how diverse mam­malian fore­run­ners were in both feed­ing and loco­mo­tor adap­ta­tions. The ground­work for mam­mals’ suc­cess­ful diver­si­fi­ca­tion today appears to have been laid long ago.

Zhe-​Xi Luo, PhD, pro­fes­sor of organ­is­mal biol­ogy and anatomy at the Uni­ver­sity of Chicago

Adap­ta­tions in anatomy, lifestyle and diet
The abil­ity to glide in the air is one of the many remark­able adap­ta­tions in mam­mals. Most mam­mals live on land, but volant mam­mals, includ­ing fly­ing squir­rels and bats that flap bird-​like wings, made an impor­tant tran­si­tion between land and aer­ial habi­tats. The abil­ity to glide between trees allowed the ancient ani­mals to find food that was inac­ces­si­ble to other land ani­mals. That evo­lu­tion­ary advan­tage can still be seen among today’s mam­mals such as fly­ing squir­rels in North Amer­ica and Asia, scaly-​tailed glid­ers of Africa, mar­su­pial sugar glid­ers of Aus­tralia and colu­gos of South­east Asia.

The Juras­sic Maiopatag­ium and Vilevolodon are stem mam­mali­aforms, long-​extinct rel­a­tives of liv­ing mam­mals. They are haramiyi­dans, an entirely extinct branch on the mam­malian evo­lu­tion­ary tree, but are con­sid­ered to be among fore­run­ners to mod­ern mam­mals. Both fos­sils show the exquis­itely fos­silized, wing-​like skin mem­branes between their front and back limbs. They also show many skele­tal fea­tures in their shoul­der joints and fore­limbs that gave the ancient ani­mals the agility to be capa­ble glid­ers. Evo­lu­tion­ar­ily, the two fos­sils, dis­cov­ered in the Tiao­jis­han For­ma­tion north­east of Bei­jing, China, rep­re­sent the ear­li­est exam­ples of glid­ing behav­iour among extinct mam­mal ancestors.

The two newly dis­cov­ered crea­tures also share sim­i­lar ecol­ogy with mod­ern glid­ers, with some sig­nif­i­cant dif­fer­ences. Today, the hall­mark of most mam­mal glid­ers is their her­biv­o­rous diet that typ­i­cally con­sists of seeds, fruits and other soft parts of flow­er­ing plants. But Maiopatag­ium and Vilevolodon lived in a Juras­sic world where 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, and their way of life was also asso­ci­ated with feed­ing on these entirely dif­fer­ent plants. This dis­tinct diet and lifestyle evolved again some 100 mil­lion years later among mod­ern mam­mals, in exam­ples of con­ver­gent evo­lu­tion and ecology.

It’s amaz­ing that the aer­ial adap­tions occurred so early in the his­tory of mam­mals,” said study co-​author David Gross­nickle, a grad­u­ate stu­dent at the Uni­ver­sity of Chicago. “Not only did these fos­sils show exquis­ite fos­siliza­tion of glid­ing mem­branes, their limb, hand and foot pro­por­tion also sug­gests a new glid­ing loco­mo­tion and behaviour.”

Thriv­ing among dinosaurs
Early mam­mals were once thought to have dif­fer­ences in anatomy from each other, with lim­ited oppor­tu­ni­ties to inhabit dif­fer­ent envi­ron­ments. The new glider fos­sils from the dinosaur-​dominated Juras­sic Period, along with numer­ous other fos­sils described by Luo and col­leagues in the last 10 years, how­ever, pro­vide strong evi­dence that ances­tral mam­mals adapted to their wide-​ranging envi­ron­ments despite com­pe­ti­tion from dinosaurs.

Mam­mals are more diverse in lifestyles than other mod­ern land ver­te­brates, but we wanted to find out whether early fore­run­ners to mam­mals had diver­si­fied in the same way,” Luo said. “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.”

(Source: Uni­ver­sity of Chicago, med­i­cine & bio­log­i­cal sci­ences press release, 07.008.2017)

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