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Dino flew like a “biplane”

Jan. 21, 2007
Courtesy PNAS
and World Science staff

The Wright broth­ers weren’t the first to come up with their trade­mark, dou­ble-deck­er de­sign for air­craft wings, if two sci­en­tists are cor­rect.

A re­eva­l­u­a­tion of fos­sils, they say, sug­gests that the ear­li­est fly­ing di­no­saurs al­so found flight suc­cess us­ing two sets of wings like a bi­plane. 

The Wright Brothers in 1901. (Photo by Octave Chanute; Library of Congress)

The stu­dy, by Sankar Chat­ter­jee of the Mu­se­um of Tex­as Tech Uni­ver­si­ty in Lub­bock, Tex­as, and re­tired Ca­na­di­an aer­o­nau­ti­cal en­gi­neer R. Jack Tem­plin, ap­pears in this week’s ad­vance on­line is­sue of the re­search jour­nal Pro­ceed­ings of the Na­tio­n­al Aca­de­my of Sci­en­ces.

The an­ces­tors of mod­ern birds are be­lieved to have been small, feath­ered tree-dwel­ling di­no­saurs that de­vel­oped wings to glide be­tween tree­tops. 

Mi­cro­rap­tor gui, one of the ear­li­est of these, lived about 125 mil­lion years ago and ap­par­ent­ly used four wings. It had long, asym­met­ric flight feath­ers on both its fore­limbs and its feet, ac­cord­ing to researchers. 

Top: sketch of Mi­cro­rap­tor gui, as pre­served. Bot­tom: di­a­gram of the "biplane" lay­out as seen from the side. The shad­ed, teardrop-shaped forms rep­re­sent the wings. (Cour­te­sy PNAS)

A 2003 study of fos­sils from Chi­na con­c­lu­ded that Mi­cro­rap­tor prob­ably spread its legs out­ward and held its wings with one pair be­hind the oth­er, like dra­gon­flies. 

The new study offers an al­ter­na­tive hy­poth­e­sis. Eval­u­a­tions of limb joints and feath­er ori­en­ta­tion in­di­cate the wing lay­out pre­vi­ously in­ferred would­n’t have of­fered suit­a­ble lift or en­abled the beast to walk, ac­cord­ing to the au­thors. 

In­stead, they pro­pose that the legs were po­si­tioned be­low the body, pro­d­uc­ing a bi­plane-like de­sign. 

A com­put­er flight sim­u­la­tion us­ing this de­sign showed that Mi­cro­rap­tor would un­du­late up and down, an ideal ap­proach for glid­ing among trees, they added. 

Wheth­er a bi­plane-like phase rep­re­sented a pre­cur­sor to all bird flight or was a failed off­shoot is un­cer­tain, the pair con­tin­ued, but they said most fos­sil ev­i­dence points to the form­er.

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The Wright brothers weren’t the first to come up with their trademark, double-decker design for aircraft wings, if two scientists are correct. A reevaluation of fossil remains, they say, suggests that the earliest flying dinosaurs also found flight success using two sets of wings like a biplane. The study, by Sankar Chatterjee of the Museum of Texas Tech University in Lubbock, Texas, and retired Canadian aeronautical engineer R. Jack Templin, appears in this week’s advance online issue of the research journal pnas. The ancestors of modern birds are believed to have been small, feathered tree-dwelling dinosaurs that developed wings to glide between treetops. Microraptor gui, one of the earliest of these, lived about 125 million years ago and utilized four wings. as it had long and asymmetric flight feathers on both its hands and feet. A 2003 study of fossils from China suggested Microraptor spread its legs out to the sides and held its wings with one pair behind the other, like dragonflies. The new study offers an alternative hypothesis. Evaluations of limb joints and feather orientation indicate the wing layout previously inferred wouldn’t have offered suitable lift or enabled the beast to walk, according to the authors. Instead, they propose that the hindlegs were positioned below the body, adopting a biplane-like design. A computer flight simulation using this design showed that Microraptor would undulate up and down, an ideal approach for gliding among trees, they added. Whether a biplane-like phase represented a precursor to all bird flight or was a failed offshoot is uncertain, the pair continued, but they said most fossil evidence points to the former scenario.