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Dinosaur molecules decoded

April 12, 2007
Courtesy Harvard Medical School
and World Science staff

In a ven­ture once thought to lie out­side the reach of sci­ence, re­search­ers have de­cod­ed the make­up of mo­le­cules from soft tis­sue of a 68 mil­lion-year-old Ty­ran­no­saur­us rex.

Sci­en­tists with Har­vard Med­i­cal School and Beth Is­ra­el Dea­con­ess Med­i­cal Cen­ter in Bos­ton ex­am­ined pro­teins, or­gan­ic mo­le­cules made up of strings of am­ino ac­ids. 

The ex­ist­ence of such an­cient pro­tein de­fies long­stand­ing wis­dom, re­search­ers said. When an an­i­mal dies, pro­tein im­me­di­ate­ly be­gins to de­grade and, in the case of fos­sils, is slow­ly re­placed by min­er­al. This sub­sti­tu­tion pro­cess was thought to be com­plete by one mil­lion years.

The sev­en stud­ied pro­tein frag­ments ap­pear to most close­ly match ami­no ac­id se­quences found in chick­ens, the sci­en­tists said. That would seem to con­firm that birds are de­scended from di­no­saurs, the pre­vail­ing mod­ern view.

The pro­teins formed part of col­la­gen, a com­po­nent of car­ti­lage and oth­er con­nec­tive tis­sue. 

“Most peo­ple be­lieve that birds evolved from di­no­saurs, but that’s all based on the ar­chi­tec­ture of the bones,” said John Asara of Beth Is­ra­el Dea­con­ess. “This al­lows you to get the chance to say, ‘Wait, they real­ly are re­lat­ed be­cause their se­quences are re­lat­ed.’ We did­n’t get enough se­quences to de­fin­i­tive­ly say that, but what se­quences we got sup­port that idea.”

The find­ings ap­pear in the April 13 is­sue of the re­search jour­nal Sci­ence.

Mary Schweit­zer of North Car­o­li­na State Uni­ver­si­ty in Ra­leigh, N.C., one of the dis­cov­er­ers of the soft tis­sue frag­ments, and col­leagues pre­sented sep­a­rate ev­i­dence for the T. rex-bird con­nec­tion in the same is­sue of the jour­nal. They found that ex­tracts of T. rex bone re­acted with an­ti­bod­ies to chick­en col­la­gen. 

“For cen­turies it was be­lieved that the pro­cess of fos­sil­i­za­tion de­stroyed any orig­i­nal ma­te­ri­al,” said Schweit­zer. “Con­se­quent­ly, no one looked care­ful­ly at real­ly old bones.”

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Homepage image: "Awakening of Hunger" (Tyrannosaurus Rex), © 1985 Mark Hallett

In a venture once thought to lie outside the reach of science, researchers have decoded the makeup of molecules from soft tissue of a 68 million-year-old Tyrannosaurus rex. Scientists with Harvard Medical School and Beth Israel Deaconess Medical Center in Boston examined protein molecules, organic compounds made up of strings of animo acids. The existence of such ancient protein defies longstanding wisdom, researchers said. When an animal dies, protein immediately begins to degrade and, in the case of fossils, is slowly replaced by mineral. This substitution process was thought to be complete by one million years. The seven studied protein fragments appear to most closely match amino acid sequences found in chickens, the scientists said. That would seem to confirm that birds are descended from dinosaurs, the prevailing modern view. The proteins form part of collagen, a component of cartilage and other connective tissue. “Most people believe that birds evolved from dinosaurs, but that’s all based on the architecture of the bones,” said John Asara of Beth Israel Deaconess. “This allows you to get the chance to say, ‘Wait, they really are related because their sequences are related.’ We didn’t get enough sequences to definitively say that, but what sequences we got support that idea.” The findings appear in the April 13 issue of the research journal Science. Mary Schweitzer of North Carolina State University in Raleigh, N.C., one of the discoverers of the soft tissue fragments, and colleagues presented separate evidence for the T. rex-bird connection in the same issue of the journal. They found that extracts of T. rex bone reacted with antibodies to chicken collagen. “For centuries it was believed that the process of fossilization destroyed any original material, consequently no one looked carefully at really old bones,” said Schweitzer.