Have we really discovered fragments of DNA from dinosaurs 75 million years old?

An international team of paleontologists is intrigued by structures and molecules found in the fossilized remains of a 75 million-year-old duckbill dinosaur. Cautious, and although everything indicates that Jurassic Park is intended to remain science fiction, the researchers wonder if they are not in front of DNA fragments and fossilized cells. Colleagues are skeptical.

A dinosaur enthusiast has exactly the same reactions as paleontologists Alan Grant and Ellie Sattler, when they first discover a brachiosaurus living in Jurassic Park, by reading the title of a press release from the Chinese Academy of Sciences: Cartilage Cells, Chromosomes and DNA Preserved in 75 Million-Year-Old Baby Duckbilled Dinosaur. The French translation giving “ Cartilage cells, chromosomes and DNA kept in a baby dinosaur at beak 75 million year old duck " The same enthusiast will also have as a second reaction the needle of his “bullshitometer” which will jump because he knows that all the studies done so far indicate that DNA cannot survive beyond a few million years and again under conditions that would be exceptional.

One of the mythical scenes of Jurassic Park. © Gagtiger

The press release refers to a publication by an international team of paleontologists in National Science Review and the title as well as the content of the article are much less affirmative. We see structures at microscope in fossilized bones that look like cells with fossilized nuclei and chromosomes. Biochemical tests can be interpreted by the presence of DNA which does not come from a contamination But the researchers insist on caution and do not at all claim that they have indeed discovered dinosaur DNA remains, even if they think they have disturbing arguments in this direction.

Dinosaurs discovered by the real paleontologist of Jurassic Park

There are still several indirect links with Jurassic Park, first of all because it is co-signed by Jack horner, the paleontologist who served as scientific adviser to Steven Spielberg for his film and also by two of the former PhD students of Horner, respectively stationed at theInstitute of Vertebrate Paleontology and Paleoanthropology (IVPP) of the Chinese Academy of Sciences and at the North carolina state university, Alida Bailleul and Mary Schweitzer.

The two researchers and their colleagues exhibit work in gestation for almost a decade when Alida Bailleul, then in PhD, used her microscopy skills to study sections of fossilized bones of dinosaurs and in particular those of skulls of babiesHypacrosaurus stebingeri. Bones found in a nest of this species belonging to an extinct genus of ornithopod dinosaurs, from the family of hadrosaurids, discovered in the famous badlands from Montana in 1988 by Horner. The fossils of this dinosaur herbivore duckbill dated Cretaceous, more specifically about 75 million years ago. The first fossilized remains of Hypacrosaurus have been discovered by the American paleontologist Barnum Brown to whom we owe, in 1902, the discovery of the famous Tyrannosaurus rex.

Alida Bailleul had under her eyes preserved circular structures in fossils that resembled those of cartilage cells, chondrocytes, but calcified, with small dark regions inside resembling cell nuclei and chromosomes. The researcher could not believe her impressions until a meeting shortly after with Mary Schweitzer, who had published controversial results on fossilized remains of dinosaur cells, and even traces of some of their protein.

"The skull bones of baby dinosaurs are not melted when they hatch, but instead, some of them have cartilaginous plaques that later fuse into bones in the spaces between them. Seeing deliciously preserved microscopic structures that looked like specific types of cells found only in cartilage, and which would have been present in the living organism in these tissues, led us to hypothesize that cell conservation could extend at the molecular level ", explains Alida Bailleul in a press release from the North carolina state university.

Molecules that react like DNA fragments

To find out more, the researchers carried out comparative immunological and histochemical tests between what appeared to be dinosaur cartilage and that of a skull.bird modern, an emu, at a similar stage of development. The reason is explained by Mary Schweitzer, still in the same press release.

"The skulls of birds ossify or harden, in the same way as the skull of this hadrosaur, and primitive birds like the emus are the closest relatives we have in life today of non-avian dinosaurs. "

It was first to prove that we were in the presence of calcified cartilage by finding there remains of a protein which is a marker of cartilage and not of a non-cartilaginous bone tissue, the collagen II. As in the case of an emu, antibody anticollagen II reacted with the supposed calcified remains of cartilage and not with the surrounding fossilized bone, which is consistent with the fact that collagen I dominates in the bones.

“These tests show how specific the antibodies are to each type of protein and support the presence of collagen II in these tissues. Moreover, the bacteria cannot produce collagen, which excludes contamination as a source of molecules ", says Schweitzer.

As for an extraordinary assertion which, as we know, requires extraordinary proof, we are not there with DNA as Mary Schweitzer and her colleagues recognize, but the argument used seems disturbing. They used histochemical dyes, DAPI (4 ′, 6-diamidino-2-phenylindole) and PI (propidium iodide), which are generally known to only be able to bind to DNA fragments.

The researchers then obtained results which Mary Schweitzer exposes in these terms: "The dyes show a point reactivity, which means that they bind to specific molecules within the microstructure and which are not spread over the whole cell as one would expect if these molecules were the result of bacterial contamination. ". But as the paleontologist also explains in a long article by National Geographic : "I don't even want to call them DNA because I'm careful and I don't want to overestimate the results. There is something in these cells that is chemically consistent with and that reacts like DNA ". A statement she had already made a few years ago when she thought she had already made a similar discovery (as she explains in the ehealth below), even insisting that it was highly unlikely that Jurassic Park would become one day a reality.

To try to make credible a seemingly impossible conservation of DNA, the researchers have several hypotheses. Cartilage is not porous like bone, which would have isolated and protected DNA and cells to the point that we can find the traces observed today. Of chemical bonds extra strands of DNA fragments could also have consolidated the molecules. In any event, if DNA has been well preserved, the fragments are very probably compared to the genome of his dinosaur, as are a few isolated sentences compared to a complete novel. We could perhaps luckily have some information on the biology of the dinosaurs but we should not expect more.

An interview with Mary Schweitzer and her research on dinosaur DNA and proteins for years. To obtain a fairly faithful translation into French, click on the white rectangle at the bottom right. English subtitles should then appear. Then click on the nut to the right of the rectangle, then on "Subtitles" and finally on "Translate automatically". Choose "French". © UNC-TV Science

Yes, dinosaur cells have surely reached us!

Article by Quentin Mauguit published on October 24, 2012

In recent years, soft tissue has been found in several dinosaur bones. Proteins stored for tens of millions of years have just confirmed the animal origin of these cells. Even better, DNA remains may have been found, but we can't conclude anything … yet!

A T-rex that died 68 million years ago has regularly returned to the forefront since the publication of its discovery in 2005. Its particularity? Mary Schweitzer of the North carolina state university would have found soft tissueincluding what appear to be blood vessels transparencies, inside a femur broken. However, they are not supposed to resist the fossilization.

After dissolution of a bone sample, proteins were recovered for analysis. They turned out to be collagen, a fiber-forming molecule within the extracellular matrix organisms. In 2007, its structure was partially sequenced and then compared to the proteins currently found in several animal species. A strong link has been established with the chicken collagen, a descendant of dinosaurs like all birds. This relationship has been confirmed by immunohistochemical studies.

Despite this result, controversies persist on the nature of the structures observed. Some scientists believe that soft tissue corresponds to a bacterial biofilm and not to an assembly of cells from the Cretaceous. Mary Schweitzer may have just closed the debate with the publication of new data in the journal Bone. The cells found would be good, on the basis of molecular and immunological analyzes, of animal origin. Even better, they may contain DNA remains!

New evidence of kinship between dinosaurs and birds

Starry cells resembling osteocytes were extracted from the bones of the T-rex and from a Brachylophosaurus canadensis having lived 80 million years ago. They were then exposed to antibodies which specifically bound to PHEX proteins displaying a epitope, a fixation site, OB 3.7. The response has been positive. Two conclusions are necessary. First, the cell is of animal origin. Bacteria do not in fact have a PHEX protein. Second, the osteocytes would be related to those currently encountered in birds, only to have the OB 3.7 epitope. The cells analyzed therefore more than likely belonged to the dinosaurs.

Antibodies that specifically bind to the sugar-phosphate column ofDNA were then used to search for the presence of material genetic. Researchers observed localized positive responses in both dinosaur species. Additional analyzes then highlighted the presence of histone4, a protein closely associated with DNA in animals. There was therefore no bacterial contamination.

The mass spectrometry allowed to find molecules ofactin and tubulin, two major constituents of cytoskeleton. Of bacteria also have these proteins, but not those that were present in sediment surrounding the bones found.

All of these cellular proteins would therefore have been well preserved for tens of millions of years, just like the osteocytes analyzed! No conclusions can be drawn about DNA, which could of course come from other animals. The structures that reacted to the tests will now have to be sequenced to reveal their secrets. Remember, theDeoxyribonucleic acid has, according to a recent study, a duration theoretical maximum life of 6.8 million years, under the best possible conservation conditions.

This will also interest you

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