"Long before it's in the papers"
January 27, 2015


Why did dinos have feathers long before flight?

Oct. 30, 2014
Courtesy of University of Bonn
and World Science staff

Why were di­no­saurs cov­ered in feath­ers long be­fore the early bird spe­cies Ar­chae­op­ter­yx first at­tempted flight?

Sci­en­tists try to an­swer that in an ar­ti­cle in the lat­est is­sue of the re­search jour­nal Sci­ence. They pro­pose that these an­cient lizards had a highly de­vel­oped col­or sen­si­ti­vity, and that feath­ers made them more col­orful, aid­ing com­mu­nica­t­ion, mate se­lec­tion and pro­crea­t­ion.

These mod­ern feath­ers show a ra­di­ant em­er­ald green as a re­sult of the light-refracting nano-struc­tures in­side. Their flat, con­sist­ent­ly branch­ing struc­ture al­so works to pro­duce the strik­ing me­tal­lic sheen. This spec­i­men is from the col­lec­tion at the In­sti­tute for Zo­ol­o­gy at the Uni­ver­si­ty of Bonn in the Pop­pels­dorf Pal­ace. (Pho­to: Ge­org Oleschin­ski/U­niv. Bonn)

The idea that birds and di­no­saurs are close rel­a­tives dates back to the 1800s, when the fa­ther of ev­o­lu­tion­ary the­o­ry, Charles Dar­win, was at work. But it took over 130 years for the first real proof to come to light with many disco­veries of fos­sils of feath­ered di­no­saurs, mainly in Chi­na.

Thanks to these finds, sci­en­tists now be­lieve that birds de­scend from a branch of me­di­um-sized pred­a­to­ry di­no­saurs called the­ro­pods, such as Ty­ran­no­saur­us rex and al­so ve­loci­rap­tors, made fa­mous by the film Ju­ras­sic Park. 

Many of them, in­clud­ing pos­sibly T. rex, had feath­ers. But why did they, if they could­n’t fly?

“Up un­til now, the ev­o­lu­tion of feath­ers was mainly con­sid­ered to be an adapta­t­ion re­lat­ed to flight or to warm-blood­edness, sea­soned with a few specula­t­ions about dis­play ca­pa­bil­i­ties,” said Marie-Claire Kosch­owitz of the Uni­vers­ity of Bonn in Germany, an au­thor of the pa­per. 

“I was nev­er really con­vinced by any of these the­o­ries. There has to be some par­tic­u­larly im­por­tant fea­ture at­tached to feath­ers that makes them so un­ique and caused them to spread so rap­idly amongst the an­ces­tors of the birds we know to­day.”

She now sug­gests this fea­ture is found in di­no­saurs’ col­or vi­sion. Af­ter an­a­lyz­ing di­no­saurs’ ge­net­ic rela­t­ion­ships to rep­tiles and birds, she con­clud­ed that di­no­saurs could see not only the col­ors we can dis­cern, but al­so ul­tra­vi­o­let. 

Mam­mals gen­er­ally have rath­er poor col­or vi­sion or even none be­cause they tended to be noc­tur­nal dur­ing the early stages of their ev­o­lu­tion. But many stud­ies on the so­cial be­hav­ior and mate choice among rep­tiles and birds, which are ac­tive dur­ing the day, have found that they re­spond to ul­tra­vi­o­let.

The pre­cur­sors to feath­ers re­sem­bled hairs si­m­i­lar to mam­mals’ fur, the au­thors ex­plain. These strands served mainly to help keep the smaller pred­a­to­ry di­no­saurs, which would eventually give rise to birds, warm. But they weren’t very col­orful. They eventually evolved in­to flat feath­ers, which could dis­play of an al­most in­fi­nite va­ri­e­ty of col­ors while still pro­vid­ing in­sula­t­ion. Their broad sur­face ar­ea, cre­at­ed by in­ter­locked strands of a ma­te­ri­al called ker­a­tin, al­lows for the bend­ing of light, called re­frac­tion, pro­duc­ing col­or.

“This al­lowed di­no­saurs to not only show off their col­orful feath­ery at­tire, but to be warm-blood­ed an­i­mals at the same time – some­thing mam­mals nev­er man­aged,” said co-au­thor Mar­tin Sand­er of the uni­vers­ity.

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Why were dinosaurs covered feathers long before the early bird species Archaeopteryx first attempted flight? Scientists try to answer that question in an article in the latest issue of the research journal Science. They propose that these ancient lizards had a highly developed color sensitivity, and that feathers made them more colorful, aiding communication, mate selection and procreation. The idea that birds and dinosaurs are close relatives dates back to the 1800s, when the father of evolutionary theory, Charles Darwin, was at work. But it took over 130 years for the first real proof to come to light with many discoveries of fossils of feathered dinosaurs, mainly in China. Thanks to these finds, scientists now believe that birds descend from a branch of medium-sized predatory dinosaurs called theropods, such as Tyrannosaurus rex and also velociraptors, made famous by the film Jurassic Park. Many of them, including possibly T. rex, had feathers. But why did they, if they couldn’t fly? “Up until now, the evolution of feathers was mainly considered to be an adaptation related to flight or to warm-bloodedness, seasoned with a few speculations about display capabilities,” said Marie-Claire Koschowitz of the University of Bonn in Germany, an author of the paper. “I was never really convinced by any of these theories. There has to be some particularly important feature attached to feathers that makes them so unique and caused them to spread so rapidly amongst the ancestors of the birds we know today.” She now suggests this feature is found in dinosaurs’ color vision. After analyzing dinosaurs’ genetic relationships to reptiles and birds, she concluded that dinosaurs could see not only the colors we can discern, but also ultraviolet. Mammals generally have rather poor color vision or even none because they tended to be nocturnal during the early stages of their evolution. But many studies on the social behavior and mate choice among reptiles and birds, which are active during the day, have found that they respond to ultraviolet. The precursors to feathers resembled hairs similar to mammals’ fur, the authors explain. These strands served mainly to help keep the smaller predatory dinosaurs, which would eventually give rise to birds, warm. But they weren’t very colorful. They eventually evolved into flat feathers, which could display of an almost infinite variety of colors while still providing insulation. Their broad surface area, created by interlocked strands of a material called keratin, allows for the bending of light, called refraction, producing color. “This allowed dinosaurs to not only show off their colorful feathery attire, but to be warm-blooded animals at the same time – something mammals never managed,” said co-author Martin Sander of the university.