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Challenge to dino-bird evolution theory not dead yet

Feb. 10, 2010
Courtesy Oregon State University
and World Science staff

Al­though most sci­en­tists ac­cept that birds de­scended from di­no­saurs, chal­lenges to the idea aren't dead yet.

A study just pub­lished in the re­search jour­nal Pro­ceed­ings of the Na­tional Acad­e­my of Sci­ences pro­vides yet more ev­i­dence against the the­o­ry, ac­cord­ing to some.

A 1915 drawing by nat­u­ral­ist Wil­liam Bee­be sug­gests a hy­po­thet­i­cal view of what ear­ly birds may have looked like, glid­ing down from trees. The pic­ture bears a strik­ing sim­i­lar­i­ty, some sci­en­tists say, to a fos­sil dis­cov­ered in 2003 that is rais­ing new doubts about wheth­er birds de­scended from ground-dwelling the­ro­pod di­no­saurs. (Pho­to cour­te­sy Or­e­gon State Uni­ver­si­ty)


The anal­y­sis was done of an un­usu­al fos­sil dis­cov­ered in 2003 called “mi­cro­rap­tor.” Three-di­men­sion­al mod­els were used to study its pos­si­ble flight po­ten­tial. The ass­ess­ment con­clud­ed this small, feath­ered spe­cies must have been a “glid­er” that came down from trees. 

The re­search is sol­id and con­sist­ent with a string of stud­ies in re­cent years that pose in­creas­ing chal­lenge to the birds-from-di­no­saurs the­o­ry, said John Ruben, a pro­fes­sor of zo­ol­o­gy at Or­e­gon State Uni­vers­ity who au­thored a com­men­tary in the jour­nal on the new re­search.

A long list of com­monal­i­ties be­tween birds, rep­tiles and cer­tain di­no­saurs—including si­m­i­lar­i­ties in bone struc­tures at both the mi­cro­scop­ic and vis­i­ble lev­el­s—have drawn most pa­le­on­tol­ogists to­ward the con­ven­tion­al view of di­no­saur-bird ev­o­lu­tion. In it, birds descended from the­ro­pod di­no­saurs, a great lineage of ground-dwelling meat-eaters with strong hind legs and short fore­limbs.

Yet some are draw­ing to­tally dif­fer­ent con­clu­sions.

The weight of the ev­i­dence is now sug­gest­ing that not only did birds not de­scend from di­no­saurs, Ruben said, but that some spe­cies thought to be di­no­saurs may have de­scended from birds. “We're fi­nally break­ing out of the con­ven­tion­al wis­dom of the last 20 years, which in­sisted that birds evolved from di­no­saurs and that the de­bate is all over and done with,” Ruben said. “This is­sue is­n't re­solved at all.”

Al­most 20 years of re­search at Or­e­gon State on the forms of birds and di­no­saurs, along with oth­er stud­ies, Ruben said, are much more con­sist­ent anoth­er view: that birds may have had an an­cient com­mon an­ces­tor with di­no­saurs, but they evolved sep­a­rately on their own path. 

Af­ter mil­lions of years of sep­a­rate ev­o­lu­tion, ac­cord­ing to this view, birds al­so gave rise to the rap­tors, which “look quite a bit like di­no­saurs but they have much more in com­mon with birds than they do with oth­er the­ro­pod di­no­saurs such as Tyran­nosaurus [Rex],” Ruben said.

“We think the ev­i­dence is fi­nally show­ing that these [rap­tors] which are usu­ally con­sid­ered di­no­saurs were ac­tu­ally de­scended from birds, not the oth­er way around,” Ruben added. Small an­i­mals such as ve­loci­rap­tor that have gen­er­ally been thought to be di­no­saurs are more likely flight­less birds, he said.

Anoth­er study last year from Flor­i­da State Uni­vers­ity raised si­m­i­lar doubts, Ruben noted.

In the newly pub­lished work, University of Kansas sci­en­tists ex­am­ined a fos­sil that showed feath­ers on all four limbs, some­what re­sem­bling a bi-plane. Glide tests based on its struc­ture con­clud­ed it would not have been prac­ti­cal for it to have flown from the ground up, but it could have glid­ed from the trees down, some­what like a mod­ern-day fly­ing squir­rel. Many re­search­ers have long be­lieved that glid­ers such as this were the an­ces­tors of mod­ern birds.

“This mod­el was not con­sist­ent with suc­cess­ful flight from the ground up, and that makes it pret­ty dif­fi­cult to make a case for a ground-dwelling the­ro­pod di­no­saur to have de­vel­oped wings and flown away,” Ruben said. “On the oth­er hand, it would have been quite pos­si­ble for birds to have evolved and then, at some point, have var­i­ous spe­cies lose their flight ca­pa­bil­i­ties and be­come ground-dwelling, flight­less an­i­mals – the rap­tors. This may be hugely up­set­ting to a lot of peo­ple, but it makes per­fect sense.”

The study appeared in the Proceedings ear­ly on­line issue for the week of Jan. 25, where­as Ru­ben’s com­ment­ary was pub­lished in early on­line is­sue for the week of Feb. 8.

“Pesky new fos­sils... sharply at odds with con­ven­tion­al wis­dom nev­er seem to cease pop­ping up,” Ruben wrote in his article.


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Although most scientists accept that birds descended from dinosaurs, challenges to the idea aren't dead yet. A new study just published in the research journal Proceedings of the National Academy of Sciences provides yet more evidence against the theory, according to its authors. The analysis was done of an unusual fossil specimen discovered in 2003 called “microraptor,“ in which three-dimensional models were used to study its possible flight potential. The study concluded this small, feathered species must have been a “glider“ that came down from trees. The research is solid and consistent with a string of studies in recent years that pose increasing challenge to the birds-from-dinosaurs theory, said John Ruben, a professor of zoology at Oregon State University who authored a commentary in the journal accompanying the new research. A long list of commonalities between birds, reptiles and certain dinosaurs—including similarities in bone structures at both the microscopic and visible levels—have drawn the majority of paleontologists toward the conventional view of dinosaur-bird evolution. Yet some are drawing totally different conclusions. The weight of the evidence is now suggesting that not only did birds not descend from dinosaurs, Ruben said, but that some species now believed to be dinosaurs may have descended from birds. “We're finally breaking out of the conventional wisdom of the last 20 years, which insisted that birds evolved from dinosaurs and that the debate is all over and done with,“ Ruben said. “This issue isn't resolved at all.“ Almost 20 years of research at Oregon State on the forms of birds and dinosaurs, along with other studies, Ruben said, are much more consistent another view: that birds may have had an ancient common ancestor with dinosaurs, but they evolved separately on their own path. After millions of years of separate evolution, according to this view, birds also gave rise to the raptors, which “look quite a bit like dinosaurs but they have much more in common with birds than they do with other theropod dinosaurs such as Tyrannosaurus,“ Ruben said. Theropods were a lineage of meat-eating dinosaurs with strong hind legs and short forelimbs. “We think the evidence is finally showing that these animals which are usually considered dinosaurs were actually descended from birds, not the other way around,“ Ruben added. Small animals such as velociraptor that have generally been thought to be dinosaurs are more likely flightless birds, he said. Another study last year from Florida State University raised similar doubts, Ruben said. In the newly published work, scientists examined a remarkable fossil that had feathers on all four limbs, somewhat resembling a bi-plane. Glide tests based on its structure concluded it would not have been practical for it to have flown from the ground up, but it could have glided from the trees down, somewhat like a modern-day flying squirrel. Many researchers have long believed that gliders such as this were the ancestors of modern birds. “This model was not consistent with successful flight from the ground up, and that makes it pretty difficult to make a case for a ground-dwelling theropod dinosaur to have developed wings and flown away,“ Ruben said. “On the other hand, it would have been quite possible for birds to have evolved and then, at some point, have various species lose their flight capabilities and become ground-dwelling, flightless animals – the raptors. This may be hugely upsetting to a lot of people, but it makes perfect sense.“ “Pesky new fossils... sharply at odds with conventional wisdom never seem to cease popping up,“ Ruben wrote in his commentary. “Given the vagaries of the fossil record, current notions of near resolution of many of the most basic questions about long-extinct forms should probably be regarded with caution.“