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Shrinking dinosaurs evolved into flying birds, scientists say

July 31, 2014
Courtesy of the University of Southampton
and World Science staff

Mas­sive, meat-eating, walk­ing di­no­saurs evolved in­to ag­ile fly­ing birds by shrink­ing and shrink­ing for over 50 mil­lion years, a new study re­ports.

This adapt­abil­ity al­so helped the bird fore­run­ners sur­vive the dis­as­ter that killed off the oth­er di­no­saurs, ac­cord­ing to the stu­dy, in the lat­est is­sue of the jour­nal Sci­ence.

The re­search­ers pre­s­ent a de­tailed family tree of di­no­saurs and their bird de­scen­dants map­ping out this un­likely trans­forma­t­ion. The tree in­di­cates that the “theropod” di­no­saurs, the branch that gave rise to birds, were the only di­no­saurs that kept get­ting in­ex­orably smaller. 

“These bird an­ces­tors al­so evolved new adapta­t­ions, such as feath­ers, wish­bones and wings, four times faster than oth­er di­no­saurs,” said study co-au­thor Dar­ren Naish, ver­te­brate pa­le­on­tol­ogist at the Uni­vers­ity of South­amp­ton in the U.K.

Courtesy of U. of Southampton

Illustration of avian size evolution.

“Birds evolved through a un­ique phase of sus­tained minia­turiza­t­ion in di­no­saurs,” added lead au­thor Mi­chael Lee of the Uni­vers­ity of Ad­e­laide in Aus­tral­ia and the South Aus­tral­ian Mu­se­um. “Be­ing smaller and light­er in the land of gi­ants, with rap­idly evolv­ing ana­tom­i­cal adapta­t­ions, pro­vid­ed these bird an­ces­tors with new ec­o­log­i­cal op­por­tun­i­ties, such as the abil­ity to climb trees, glide and fly. Ul­ti­mate­ly, this ev­o­lu­tion­ary flex­i­bil­ity helped birds sur­vive the deadly me­te­or­ite im­pact which killed off all their di­no­sau­rian cousins.” 

“The di­no­saurs most closely re­lat­ed to birds are all small, and many of them—such as the aptly named Mi­cro­rap­tor—had some abil­ity to climb and glide,” said Gar­eth Dyke of South­amp­ton.

The study ex­am­ined over 1,500 anatom­i­cal traits of di­no­saurs to re­con­struct their family tree. The re­search­ers used math­e­mat­i­cal mod­el­ing to trace evolv­ing adapt­ations and chang­ing body size over time and across di­no­saur branches. “Birds out-shrank and out-e­volved their di­no­sau­rian an­ces­tors, sur­viv­ing where their larg­er, less evolv­a­ble rel­a­tives could not,” said Lee.


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Massive, meat-eating, walking dinosaurs evolved into agile flying birds by shrinking and shrinking for over 50 million years, a new study reports. This adaptability also helped the bird forerunners survive the disaster that killed off the other dinosaurs, according to the study, in the latest issue of the journal Science. The researchers present a detailed family tree of dinosaurs and their bird descendants mapping out this unlikely transformation. The tree indicates that the “theropod” dinosaurs, the branch that gave rise to birds, were the only dinosaurs that kept getting inexorably smaller. “These bird ancestors also evolved new adaptations, such as feathers, wishbones and wings, four times faster than other dinosaurs,” said study co-author Darren Naish, vertebrate palaeontologist at the University of Southampton in the U.K. “Birds evolved through a unique phase of sustained miniaturisation in dinosaurs,” added lead author Michael Lee of the University of Adelaide in Australia and the South Australian Museum. “Being smaller and lighter in the land of giants, with rapidly evolving anatomical adaptations, provided these bird ancestors with new ecological opportunities, such as the ability to climb trees, glide and fly. Ultimately, this evolutionary flexibility helped birds survive the deadly meteorite impact which killed off all their dinosaurian cousins.” “The dinosaurs most closely related to birds are all small, and many of them—such as the aptly named Microraptor—had some ability to climb and glide,” said Gareth Dyke of Southampton. The study examined over 1,500 anatomical traits of dinosaurs to reconstruct their family tree. The researchers used mathematical modelling to trace evolving adaptions and changing body size over time and across dinosaur branches. “Birds out-shrank and out-evolved their dinosaurian ancestors, surviving where their larger, less evolvable relatives could not,” said Lee.