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If it looks like a duck
The last year’s meeting of the American Association for the Advancement of Science Mary Schweitzer, a palaeontologist at North Carolina State University, wowed participants with tales of fossil proteins. And not any old proteins, either. These proteins came from the most famous prehistoric animal of all – Tyrannosaurus rex.
At the time, her evidence came indirectly. She had found that antibodies to a common protein called collagen stuck to fossil tyrannosaur bone. That suggested the bone still contained intact collagen molecules, some 68m years after the beast had died. In this week’s Science, though, she comes back with definitive evidence. Not only has she shown that the collagen is real, she now knows something about its composition.
Dr Schweitzer’s quest started when she realised that there was more to the bone of one particular tyrannosaur fossil than initially met the eye. The beast in question had been excavated in Montana by Jack Homer, a palaeontologist believed by many to be the model for Alan Grant, the hero of “Jurassic Park”. Sliced thin, there was evidence in its leg bones of fibres that looked remarkably unaltered-and the fibres were still there when the mineral matrix of the bone had been dissolved away.
It was then that she tried the collagen antibodies and found that they stuck. Specifically, she used antibodies to a particular type of the protein, known as collagen I, that had been extracted from chickens. This suggests Tyrannosaurus rex collagen is similar to that of birds. She also compared the structure and pattern of the fibres with those of modem animals and found that the species they most resembled was the emu-also a bird and also, like Tyrannosaurus rex, bipedal.
In order to understand more about the collagen’s composition, Dr Schweitzer enlisted the help of John Asara, a chemist at Harvard University. He extracted small fragments of collagen from the fossil tissue and analysed them using mass spectroscopy. This technique identifies molecules (or fragments of molecules) from a combination of their weight and their electric charges. Knowing the weights of different sorts of atoms (and of groups of atoms that show up regularly in larger molecules, such as the 20 different amino acids from which proteins are assembled) it is usually possible to piece together fragments to form the profile of an entire protein.
This Dr Asara did for Tyrannosaurus rex collagen. And when he ran the profile he had assembled through a database of known collagens, he found it was most similar to the versions found in chickens and ostriches – substantiating Dr Schweitzer’s antibody-based hunch.
That birds are (according to the particular taste of the classifier) either the descendants of dinosaurs or actual, proper dinosaurs themselves is strongly supported by bones found in Germany and China. But it is always nice to have more than one line of evidence to back a theory up. A chicken may not look much like T. rex, but appearances can deceive.
1. Mary Schweitzer made participants shocked by
1) the bones of Tyrannosaurus rex.
2) the evidence of fossil proteins.
3) the talk about fossil protein.
4) the tales about excavations.
2. Mary Schweitzer has proved the evidence of
1) the existence of Tyrannosaurus rex.
2) the composition of collagen.
3) the bones containing collagen molecules.
4) the reality of fossil bones.
3. The bones of Tyrannosaurus rex
1) have been excavated in great numbers recently.
2) were found by Alan Grant.
3) still contain fibres.
4) were excavated in the Jurassic Park
4. The scientist has found out that T rex collagen
1) is very much alike to birds.
2) is the same as the emu’s.
3) is not found in modem species.
4) is found only in chickens.
5. In her work Dr Schweitzer
1) analised the collagen on her own.
2) weighed different fossils.
3) went to study chemistry at Harvard University.
4) asked for a chemist’s help.
6. The phrase “This Dr Asara did for Tyrannosaurus rex collagen” refers to
1) the creation of a database of collagens.
2) the technique of identifying molecules.
3) the known weight of molecules.
4) the entire protein.
7. The research has shown that
1) dinosaurs are distant ancestors of modem birds.
2) Tyrannosaurus rex looked like a bird.
3) dinosaurs’ bones are mostly found in Germany and China.
4) the chicken is the closest descendant of Tyrannosaurus rex.
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