Artist's impression of the burial of the Caudipteryx. Scientists suggest that dinosaur DNA can be found in the future. Credit: Zheng Qiuyang

Scientists Say Finding Dinosaur DNA Not Impossible

What if scientists could isolate and sequence dinosaur DNA? Could this lead to the rebirth of certain prehistoric species?

Chinese paleontologists have announced the discovery of a cell nucleus containing chromatin in the fossilized cartilage of the Early Cretaceous dinosaur Caudipteryx. This is the second case of the discovery of fossil chromatin in vertebrate fossils – previously, chromatin was identified in the cartilage of a duck-billed dinosaur that lived about 70 million years ago.


Finding dinosaur DNA and what can scientists do with it?

Recent finds of cell nuclei in fossil remains

Recently, more and more reports have appeared in the scientific literature about the finds of cell nuclei in the fossil remains of organisms, starting with mammoths that lived tens of thousands of years ago, and ending with plants of the Mesozoic era or even Proterozoic embryo-like fossils with an age of about 609 million years (which, throughout apparently belong to protists).

In some cases, according to the authors of the works, the nuclei were preserved not only at the histological level, but also at the molecular level: in some fossil plants (in particular, from the Jurassic period), using histochemical methods, it was possible to identify chromatin in the nuclei – a complex of DNA with proteins.

Nuclei of fossil vertebrates

Last year, researchers used histochemistry for the first time to identify chromatin in the nuclei of fossil vertebrates. This work was led by Alida M. Bailleul of the Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences. Her team discovered cell nuclei with fragments of DNA in the fossil cartilage of the late Cretaceous duck-billed dinosaur Hypacrosaurus stebingeri, which lived about 70 million years ago.

Line drawing and the fossil of the Caudipteryx dinosaur. Credit: Zheng et al. / Communications Biology, 2021
Line drawing and the fossil of the Caudipteryx dinosaur. Credit: Zheng et al. / Communications Biology, 2021

Skepticism

Many scientists are skeptical about the work on identifying such ancient fragments of DNA since this molecule decays quite quickly by geological standards. The oldest sequenced DNA belonging to the woolly mammoth is only 1.65 million years old. Critics speculate that DNA from older fossils may in fact belong to recent bacteria ( 1, 2 ). Endogenous DNA proponents respond that the pattern of DNA distribution in fossil cells cannot be explained by bacterial origin.

Cell nuclei of dinosaurs

Recently, Alida Bayol and her colleagues from China published another work on the cell nuclei of dinosaurs. This time, paleontologists studied the fossil cartilage of the oviraptorosaurs Caudipteryx sp . (the authors do not specify the species). This dinosaur lived in the early Cretaceous period – about 125 million years ago.

Chondrocytes of Caudipteryx (a, c, d, g, h) and chicken (b, e, f) stained with hematoxylin and eosin; h - in polarized light; nu - nucleus, ct - chromatin. Credit: Zheng et al. / Communications Biology, 2021
Chondrocytes of Caudipteryx (a, c, d, g, h) and chicken (b, e, f) stained with hematoxylin and eosin; h – in polarized light; nu – nucleus, ct – chromatin. Credit: Zheng et al. / Communications Biology, 2021

Caudipteryx samples

Scientists took a sample of articular cartilage from the distal femur of the Caudipteryx and divided it into three parts. From the first two, the researchers made thin sections (thin sections), which were examined using light and electron microscopy. As a result, paleontologists discovered cartilage cells in the fossil – chondrocytes.

How did scientists examine the samples?

Scientists decalcified the third fragment in ethylenediaminetetraacetic acid for 21 days, and then prepared histological sections from it, some of which were stained with hematoxylin (stains basophilic structures, including nucleic acids, blue or purple) and eosin (stains eosinophilic structures pink ), and some were left unpainted.

The obtained sections were studied by paleontologists using light (including polarizing) microscopy and compared with similar sections of the cartilage of a modern dinosaur – a chicken. To avoid contamination, sections of Caudipteryx and chicken cartilage were cut in different rooms with different sets of instruments.

What did scientists find about the cells?

By examining the stained sections of Caudipteryx cartilage, the researchers found that most of the cells remained transparent, but in one cell, hematoxylin stained purple a rounded structure that the researchers identified as a nucleus. Moreover, it contained several dark purple filaments, which, according to the authors, were chromatin. Scientists saw a similar picture on stained sections of chicken cartilage.

Second known example

The authors note that this is the second known example of chromatin preservation in vertebrate fossils, and this chromatin is older than the previous one – from the cartilage of a duck-billed dinosaur – by 55 million years. Apparently, such ancient cellular structures were able to survive due to the special conditions of burial.

Type of tissue

According to the authors, the type of tissue also contributed to the good preservation of cellular structures: there are no vessels and nerves in the cartilage, which reduces the likelihood of bacterial colonization. In addition, chondrocytes have mainly anaerobic metabolism, so they are resistant to hypoxia and can remain viable for up to two weeks after the death of the body – that is, burial does not have to occur immediately after death.

Conclusions

The found chemical differences between the nucleus and cytoplasm in the Caudipteryx cartilage suggest that DNA may have been partially preserved in the fossils, the authors conclude. However, they stipulate that such DNA, most likely, cannot be isolated and sequenced.


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Sources:

Bressan, D. (2021, September 24). Exceptional fossil preservation suggests that discovering dinosaur dna may not be impossible. Forbes.
O’Neill, M. (2021, September 27). Potential remnants of Original DINOSAUR DNA discovered IN Exquisitely Preserved Dinosaur Cells. SciTechDaily.
Zheng, X., Bailleul, A. M., Li, Z., Wang, X., & Zhou, Z. (2021, September 24). Nuclear preservation in the cartilage of the Jehol dinosaur Caudipteryx. Nature News.

Written by Vladislav Tchakarov

Hello, my name is Vladislav and I am glad to have you here on Curiosmos. My experience as a freelance writer began in 2018 but I have been part of the Curiosmos family since mid-2020. As a history student, I have a strong passion for history and science, and the opportunity to research and write in this field on a daily basis is a dream come true.

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