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Imperial College Team IDs Biological Structures Including Amino Acids in Dinosaur Bones


NEW YORK(GenomeWeb) – Using analyses including time-of-flight secondary ion mass spectrometry, researchers from Imperial College London have detected what appear to be remnants of collagen and red blood cells in 75-million-year-old dinosaur specimens.

Significantly, said Susannah Maidment, an ICL researcher and author on the study, which was published this week in Nature Communications, the specimens examined were not especially well preserved, suggesting that preservation of the identified structures is more common than had been thought.

The findings also lend support to previous work in the field that has proven challenging to replicate — specifically, the 2005 discovery by North Carolina State University molecular paleontologist Mary Schweitzer of collagen in bones from a 68-million-year-old Tyrannosaurus rex.

Previous studies have looked at fossils as old or older than those analyzed in the Nature Communications study, Maidment told GenomeWeb. "But all those studies were based on really, really beautifully preserved fossils, in which exceptional things had to have occurred."

The ICL team's work, on the other hand, was done using what Maidment called "kind of crappy fossils." The specimens, she noted, had been part of the collection of London's Natural History Museum for roughly a century "and really had not been treated in a way that would have us expect that soft tissue [like collagen] has been preserved."

This is significant, Maidment said, in that it suggests that the features observed in the NHM fossils might be observable in a wide range of fossils.

Key to the ICL researchers' approach was the use of a focused ion beam in concert with electron microscopy to identify and extract structures of interest from within the specimens. Use of FIB to extract material for TOF-SIMS analysis let them prepare samples with clean, smooth surfaces, which "eliminates topographical artifacts common to TOF-SIMS measurements," the authors wrote.

Additionally, by drawing samples from the interior of the specimens, the researchers were able to rule out modern contamination, Maidment said. "The fact that we were getting these samples from the inside of the crystallized bone matrix itself means that contamination could never have been there."

Having obtained the material, Maidment and her colleagues analyzed them using TOF-SIMS, which gave peaks corresponding to fragments of amino acids including glycine, alanine, and proline, which are present in collagen. This, the authors noted, meshed with transmission electron microscope analysis of the same samples that identified banding patterns consistent with collagen, as well.

TOF-SIMS analysis of erythrocyte-like structures found in the fossils, meanwhile, found similarities with spectra obtained from emu blood, lending credence to the notion that they were red blood cells.

The results are interesting in part due to the fact that they support previous findings by NCSU's Schweitzer of soft tissue, including blood cells, in samples of roughly the same age, said Matthew Collins, an archaeologist at the University of York who was not involved with either study.

"There has been the perception following the work of Mary Schweitzer that her samples were somehow 'special' because that work hasn't been repeated," Collins told GenomeWeb. "So now that another laboratory has observed similar structures, that means that [the samples] are perhaps less special."

Indeed, Schweitzer's 2005 findings of soft tissue preserved in fossils that were tens of millions years old caused something of an uproar in the field, leading some to speculate that they were due to later contamination. Schweitzer and her colleagues have since performed additional analyses including mass spec- and antibody-based research to bolster their case that the soft tissue they discovered was in fact part of the original fossil. However, outside researchers have had little success replicating her findings in other samples.

This, Collins said, has had the effect of cooling the field's interest in looking for the sort of biological structures apparently detected by the ICL team in their Nature Communications study.

"We were very excited 10 years ago when Mary published her work, and it has all gone a bit quiet since," he said, adding that the ICL study might give researchers impetus to "have a go again with new techniques."

Collins cautioned, however, that while the ICL findings were "interesting and suggestive," they were not to his mind conclusive. For instance, he said, while the TOF-SIMS spectra discussed in the paper were similar in certain respects to amino acids present in collagen, there were also differences. He noted the same caveat regarding the putative erythrocyte and its similarities to emu blood.

"I think it's a good approach, a targeted approach," he said, noting as promising the fact that they did not find spectra corresponding to collagen amino acids when analyzing negative controls such as portions of the fossils without calcified fibers or on the copper grid that held the samples.

Collins added that he hoped work like the ICL study would in the future lead to information like amino acid sequence data that could prove more biologically meaningful.

The field "has found amino acids [in samples] 200, 300 million years before this, so these things aren't remarkable in that sense," he said. "The important step to me is the [amino acid] sequence data, because that is how we start to get a bit of biological data."

Maidment likewise noted this as a goal of her team's future research.

"There is a unique structure of collagen for each animal, and the more closely related two animals are, the more closely related their collagen will be," she said. "We have a fairly good idea of the framework of the family tree for Dinosauria just by the shape of the bones, but the details are still quite controversial. So, if we can find collagen in lots of different dinosaur samples and use collagen fingerprinting, then we might be able to bring an independent line of evidence about whom is most closely related to whom."

In fact, Collins and a team of international researchers published a paper in Nature earlier this year using just such an approach to illuminate the evolutionary history of a pair of South American ungulates, members of the taxa Toxodon and Macrauchenia

The samples used in that analysis were considerably younger than those used by the ICL team, however.

Collins said that he and his colleagues are currently doing experiments with the aim of establishing the rate at which molecules like DNA and proteins decompose in fossil samples. Models based on that work suggest that in cold environments collagen sequence information can be routinely recovered in samples as old as 10 million years, he said.

Maidment and her team, meanwhile, are working to better understand if there are unique qualities to the fossils they looked at that allowed them to see the biological structures they described in the study.

"We want to do a series of experiments to understand what it is that allows tissue to be preserved in these fossils," she said. "Is this sort of preservation unique to a particular environment? These fossils were found in rocks that were deposited by rivers in old floodplains. If we go look at rocks deposited in the sea, for example, would we see the same sort of preservation?"

They also plan to investigate how far back they can detect similar structures, Maidment said.

"The first dinosaurs evolved 235 million years ago. So we have a very wide range in terms of age of dinosaurs, and we'd like to see how far back we can go in the fossil record," she said.