Vol.34 No.1 2020 Science Watch Earth Sciences Earth Cartilage Cells, Chromosomes and DNA Preserved in 75 Million-Year- Old Baby Duckbilled Dinosaur

n international team led by Dr. Alida Bailleul bone. Two cartilage cells were still linked together by an from the Institute of Vertebrate Paleontology and intercellular bridge, morphologically consistent with the APaleoanthropology (IVPP) of the Chinese Academy end of cell division. of Sciences and Dr. Mary Schweitzer from North Internally, dark material resembling a cell nucleus Carolina State University in the U.S. have presented was also visible. One cartilage cell preserved dark evidence of fossilized cell nuclei and chromosomes elongated structures morphologically consistent with within preserved cartilage in baby duckbilled dinosaurs. chromosomes. “I couldn’t believe it, my heart almost Their findings were published in National Science stopped beating,” said Bailleul. Review on February 28. Bailleul and Schweitzer, together with lab director These dinosaurs belong to the genus Hypacrosaurus ZHENG Wenxia, sought to determine whether original and comes from a nesting ground discovered in 1988 molecules were also preserved in the dinosaur cartilage. by paleontologist Jack Horner in Late Cretaceous The team performed immunological and histochemical sediments of northwestern Montana. analyses on the skull of another nestling Hypacrosaurus Bailleul conducted microscopic analyses of skull from the same nesting ground. fragments from these nestling dinosaurs. In one They found that the organic matrix surrounding fragment, she noticed some exquisitely preserved cells the fossilized cartilage cells reacted to antibodies of within preserved calcified cartilage on the edges of a type II collagen, the dominant protein in all vertebrate

Reconstruction of the nesting ground of Hypacrosaurus stebingeri from the Two Medicine formation in Montana. A deceased Hypacrosaurus nestling lies with the back of its skull embedded in shallow waters. A mourning adult is portrayed on the right. (Image by Michael Rothman)

Bulletin of the Chinese Academy of Sciences 61 BCAS Vol.34 No.1 2020 Earth Sciences Earth

Cartilage cells from skull of Hypacrosaurus nestlings. (Left) Two cells at the end of cell division, showing material consistent with condensed nuclei. (Center) Higher magnification of another cell shows chromosomes. (Right) An isolated dinosaur cartilage cell reacts with the DNA stain propidium iodide (red dot, inside the cell). (Images by Alida Bailleul and ZHENG Wenxia)

cartilage. “This immunological test supports the of years, and we hope this study will encourage scientists presence of remnants of original cartilaginous proteins working on ancient DNA to push current limits and use new in this dinosaur,” said Schweitzer. methodology in order to reveal all the unknown molecular The researchers also isolated individual Hypacrosaurus secrets that ancient tissues have,” said Bailleul. cartilage cells and applied two DNA stains, DAPI and The possibility that DNA can survive for tens of PI. These bind specifically to DNA fragments in extant millions of years is not currently recognized by the material, and some of the isolated dinosaur cells showed scientific community. Rather, based upon kinetic internal, positive binding in the same pattern seen in experiments and modelling, it is generally accepted that modern cells, suggesting some original dinosaur DNA may DNA persists less than 1 million years. be preserved. These new data suggest that DNA, in some form, “These new, exciting results add to growing evidence may persist in Mesozoic tissues, and lay the foundation that cells and some of their biomolecules can persist in deep- for future efforts to recover and sequence DNA from time. They suggest DNA can be preserved for tens of millions other very ancient fossils.

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