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Scientists re-engineer bird beak to ancestral “dino” state

March 30, 2005
Courtesy 
and World Science staff

In a bid to re­trace some of the ev­o­lu­tion­ary steps that grad­u­ally trans­formed di­no­saurs in­to birds, sci­en­tists say they have re-engineered em­bry­on­ic chick­ens to grow dinosaur-like snouts.

The re­search­ers said they rep­li­cat­ed the mo­lec­u­lar pro­cesses be­hind that shift by block­ing the ac­ti­vity of the rel­a­tively mod­ern genes that con­trol beak de­vel­op­ment. In the pro­cess, they be­lieve they have out­lined a frame­work to study oth­er ev­o­lu­tion­ary tran­si­tions in a si­m­i­lar way.

An artist's rendition of the nonavian dinosaur Anchiornis and a modern bird, a tinamou. (Courtesy John Conway & Yale U.)


The re­search team, led by Yale Uni­vers­ity pa­le­on­tol­ogist and de­vel­op­mental bi­ol­o­gist Bhart-Anjan S. Bhul­lar and Har­vard Uni­vers­ity de­vel­op­mental bi­ol­o­gist Ar­hat Abzhanov, used the fos­sil rec­ord as a guide. The sci­en­tists said they trans­formed chick­en em­bryos in­to spec­i­mens with a snout and pal­ate some­what like that of small di­no­saurs such as Ve­loci­rap­tor and Ar­chae­op­ter­yx.

The goal “was to un­der­stand the mo­lec­u­lar un­der­pin­nings of an im­por­tant ev­o­lu­tion­ary tran­si­tion,” said Bhullar, lead au­thor of the stu­dy, pub­lished on­line May 12 in the jour­nal Ev­o­lu­tion. “Lit­tle work has been done on what ex­actly a beak is, an­a­tom­ic­ally, and how it got that way.”

The sci­en­tists first an­a­lyzed the anat­o­my of re­lat­ed fos­sils and liv­ing an­i­mals to out­line how the tran­si­tion might have oc­curred. Next, they searched for pos­si­ble shifts in gene ac­ti­vity, or gene “ex­pres­sion,” cor­re­lat­ing with the tran­si­tion. Fi­nally they used chem­i­cals known as small-molecule in­hibitors to block the ac­ti­vity of pre­sumed beak-spe­cif­ic genes.

This not only caused the beak to re­vert to an an­ces­tral state—it had a si­m­i­lar ef­fect on a bone at the roof of the mouth called the pal­a­tine bone, they said. This shows that “a sin­gle, sim­ple de­vel­op­mental mech­an­ism can have wide-rang­ing and un­ex­pected ef­fects,” Bhullar said.

The work took Bhullar from the al­li­ga­tor nests at Rock­e­fel­ler Wild­life Ref­uge in south­ern Lou­i­si­ana to an emu farm in Mas­sa­chu­setts. He ex­tracted DNA from var­i­ous spe­cies in or­der to clone frag­ments of ge­net­ic ma­te­ri­al to look for spe­cif­ic gene ex­pres­sion.

The re­search has sev­er­al im­plica­t­ions, Bhullar said. For ex­am­ple, if one mo­lec­u­lar mech­an­ism caused the trans­forma­t­ion, there should be a cor­re­spond­ing change in the fos­sil rec­ord. The rec­ord bears that out so far, he ar­gued. For ex­am­ple, an an­cient rel­a­tive of mod­ern birds known as Hes­per­o­nis has both the mod­ernized pal­a­tine bone and the mod­ernized beak. The lat­ter is vis­i­ble in the so-called pre­max­il­lae—bones at the tip of the up­per jaw, which in birds are en­larged and fused to form the beak.

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In a bid to retrace some of the evolutionary steps that gradually transformed dinosaurs into birds, scientists say they have re-engineered embryonic chickens to grow dinosaur-like snouts. The researchers said they replicated the molecular processes behind that shift by blocking the activity of relatively modern genes that control beak development. In the process, they believe they have outlined a framework to study other types of evolutionary transitions in a similar way. The research team, led by Yale University paleontologist and developmental biologist Bhart-Anjan S. Bhullar and Harvard University developmental biologist Arhat Abzhanov, used the fossil record as a guide. The scientists said they transformed chicken embryos into specimens with a snout and palate somewhat like that of small dinosaurs such as Velociraptor and Archaeopteryx. The goal “was to understand the molecular underpinnings of an important evolutionary transition,” said Bhullar, lead author of the study, published online May 12 in the journal Evolution. “Little work has been done on what exactly a beak is, anatomically, and how it got that way.” The scientists first analyzed the anatomy of related fossils and living animals to outline how the transition might have occurred. Next, they searched for possible shifts in gene activity, or gene “expression,” correlating with the transition. Finally they used chemicals known as small-molecule inhibitors to block the activity of presumed beak-specific genes. This not only caused the beak to revert to an ancestral state—it had a similar effect on a bone at the roof of the mouth called the palatine bone, they said. This shows that “a single, simple developmental mechanism can have wide-ranging and unexpected effects,” Bhullar said. The work took Bhullar from the alligator nests at Rockefeller Wildlife Refuge in southern Louisiana to an emu farm in Massachusetts. He extracted DNA from various species in order to clone fragments of genetic material to look for specific gene expression. The research has several implications, Bhullar said. For example, if one molecular mechanism caused the transformation, there should be a corresponding change in the fossil record. The record bears that out so far, he argued. For example, an ancient relative of modern birds known as Hesperonis has both the modernized palatine bone and the modernized beak. The latter is visible in the so-called premaxillae—small bones at the tip of the upper jaw, which in birds are enlarged and fused to form the beak.