Organic molecule remnants found in nuclei of ancient dinosaur cells

Reconstruction of Jehol Biota, and well-preserved Caudipteryx specimen. Credit: Zheng Qiuyang
Scientists from the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences and the Shandong Tianyu Museum of Nature have identified exquisitely preserved cartilage cells from a 125-million year-old dinosaur from Northeast China. These cells contain remnants of organic molecules and even chromatin. On Sept. 24, the study was published in Communications Biology.

Caudipteryx was a small, peacock-sized omnivore that had long tail feathers. It was found in the Jehol Biota, Liaoning province's shallow lakes during the Early Cretaceous.

"Geological data have accumulated over time and shown that fossil preservation was exceptional in the Jehol Biota due to fine volcanic Ash that entombed carcasses and preserved them to the cellular stage," stated Li Zhiheng Associate Professor at IVPP, and co-author of the study.

Scientists took a small piece of distal cartilage from the right side of the specimen. They then decalcified it and used different chemical and microscopy methods to analyze it. After the death of the animal, all the cells were mineralized through silicification. These cells were preserved well thanks to silicification.

They discovered two types of cells, healthy cells at the time of fossilization and unhealthy cells that had become fossilized. Alida Bailleul (Associate Professor at IVPP) and the corresponding author of the study said, "It's possible that these cells had already died before the animal died."

Cell death occurs throughout all life stages. Paleontology is a new field that allows you to place a fossilized cells in a particular spot in the cell cycle. This is the goal of the IVPP scientists: improve cell imagery in fossils.

The team also isolated cells from the body and stained them with a chemical that is used in bio-laboratories around the world. Hematoxylin is a purple chemical that binds to the cells' nuclei. One dinosaur cell was stained with hematoxylin, and it showed a purple nucleus that had some darker purple threads. The 125-million-year old dinosaur cell shows a well-preserved nucleus that retains original biomolecules and threads chromatin.

All living organisms have chromatin in their cells. It is composed of tightly packed DNA molecules. These preliminary results suggest that some remnants of dinosaur DNA might still exist. However, to confirm this, the team will need to perform more research and use more sophisticated chemical methods than the ones used here.

Alida Bailleul stated, "Let's face it, we are clearly interested in fossilized cell nuclear nuclei because that is where most DNA should be if DNA were preserved." She published a second study last year that reported exceptional preservation of biomolecules and nuclear nuclei in cartilage cells from a Montana dinosaur. We have some good preliminary data. This is very exciting. However, we are only beginning to understand the cellular biochemistry of very old fossils. We need to do more.

They insist that they must continue to analyze and develop new methods to understand how biomolecule preservation can be achieved in dinosaur cells. No one has ever succeeded in sequencing dinosaur DNA. The ancient DNA community uses sequencing methods to verify that ancient DNA has been preserved in fossils. These methods have not worked for dinosaur material, but have worked well for young fossils. Dinosaurs have been deemed too old to preserve any DNA. However, chemical data from STM and IVPP suggest otherwise.

Even though there is more data needed, this study clearly shows that fossil dinosaur cells 125 million years old cannot be considered rock. They aren't completely "stonified." They still have remnants of organic molecules. It is crucial to determine exactly what these molecules are and whether or not they contain any biological information.

More information: Zheng, X. et al. Nuclear preservation in the cartilage from the Jehol dinosaur Caudipteryx. Communications Biology (2021). Information from Communications Biology Zheng, X. et. al. (2021). DOI: 10.1038/s42003-021-02627-8