In the 125-million-year-old fossils of dinosaurs discovered in China, DNA remnants may be found. If these microscopic structures were indeed DNA, it would be the oldest known preservation of chromosome material within a vertebrate fossil.
The DNA is contained within the chromosomes of a cell's nucleus. Researchers have found evidence of cell nucleus structures in fossils from plants and algae that date back many millions of years. Scientists even suggested that nuclei might be preserved in a set microfossils dating back to 540 million years.
These claims can be controversial because it is difficult to tell a fossilized nucleus apart from random blobs of mineralization that were created during fossilization.
Reconstruction of Caudipteryx by an artist. (Zheng Qiuyang).
Researchers compared fossilized cartilage of the feathered, peacock-sized dinosaur Caudipteryx to cells from modern chickens in a new study published in Communications Biology on Sept. 24, 2012. They found structures that looked a lot like chromatin or threads of protein and DNA in the fossils.
"The fact they are seeing it is really fascinating, and it suggests that we need to continue to do more research on what happens to DNA, chromosomes, and cell death," stated Emily Carlisle, a doctoral candidate who studies microscopic fossils at the University of Bristol in England, but was not part of the new research.
Answering the burning question, "No," is not an answer.
Alida Bailleul, a paleobiologist from the Chinese Academy of Sciences, who was responsible for the new research, said in an email to Live Science, "If there's any DNA or DNA-like molecules in there, it'll be as a scientific guess very chemically modified"
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Bailleul stated that if paleontologists are able to identify chromosome material from fossils, they might be able one day to decipher a portion of a genetic sequence. This could provide some insight into the physiology of dinosaurs.
Researchers must first determine if DNA exists. Most paleontologists believed that decay and rot destroyed the cells' contents before fossilization could occur.
Carlisle explained to Live Science that any microscopic structure found in cells was considered to be collapsed cell contents. This includes organelles, membranes and other structures that have rotted prior mineralization.
Recent discoveries by paleontologists of cell structures in fossils have shown that they are legitimate. One example is the 190 million-year old fern cells, which were described in Science 2014 as a result of being buried in volcanic rock and fossilized in such a rapid manner that they were frozen during cell division. Some of these cells contain recognizable chromosomes.
Bailleul and her coworkers reported in 2020 that DNA could be preserved in the skull of an infant Hypacrosaurus. This is a type of duck-billed dinosaur, which lived 75 million years ago in Montana.
The cartilage, which is the connective tissue that forms the joints, was the site of the possible DNA.
Bailleul stated that cartilage was a good tissue for cell preservation and is more than bone.
Hidden in stone
The researchers used a well-preserved Caudipteryx specimen held by the Shandong Tianyu Museum of Nature, China for the new study.
The fossil was found in northeastern Liaoning. It has plenty of preserved cartilage that the researchers stained with the same dyes that are used to image DNA in modern tissue. These dyes are able to bind to DNA, turning it a particular color depending on which dye is used. This allows DNA to stand out from the rest of the nucleus.
(Zheng et al./Communications Biology/CC BY 4.0)
Above: A photo showing the Caudipteryx fossil on a full slab, along with a close-up view of the right vertebra (b), which is where scientists discovered the fascinating cells.
Bailleul and her colleagues examined the stained, fossilized cartilage using several microscopy techniques. They found that cartilage cells have structures that look exactly like nuclei, with chromatin in the middle.
Bailleul warned that the similarities between stained dinosaur nuclei and modern cells does not prove that there is DNA within them.
She explained that it meant that parts of original organic molecules are present, possibly some original DNA, but that we don't know for certain. We just have to figure out what these organic molecules are.
Carlisle stated that imaging clearly shows nuclei. However, it is harder to identify fossilized DNA because no one knows what happens to them as they decay.
It is possible that the nucleus contents could just collapse into structures that look like the chromosomes, but really are just a jumbled of meaningless mineralized junk. However, it is also possible that some of the original molecular structure may be preserved by fossilization.
One 2012 study found that bone DNA will be completely destroyed in 7 million years. However, the timing of this may depend on environmental factors.
Carlisle stated, "It would really be interesting to do more experiments into this, looking at what occurs inside the nuclei rather than just what happens from the surface."
Bailleul hopes to collect more chemical information with her colleagues to determine the identity of these mysterious structures.
She said, "I hope we are able to reconstruct a sequence someday, someday somehow." Let's just say that I could be wrong but also could be right.