Scientists have found remnants of DNA in the fossilized remains of a sea turtle that dates back six million years. This marks one of the rare occasions when genetic material has been identified in such ancient vertebrate fossils. The discovery paves the way for future DNA studies from fossils that could provide insights into how living creatures evolved and changed over time.
Researchers from the Universidad del Rosario in Bogota and the Smithsonian Tropical Research Institute made the find in a partial fossil excavated along Panama’s Caribbean coast in 2015. The specimen, DK 807, consists of a relatively intact carapace (shell) and parts of the turtle’s front limbs and pelvic girdle, which would have measured around one foot (30 centimeters) in length. Using solution-based examinations of the fossil’s bone cells, known as osteocytes, the scientists could recognize nuclei within the cell structures and, in turn, detect the presence of DNA.
The fossil’s bones are incredibly well-preserved, displaying “exceptional preservation of bone sutures, sulci, and sculpturing, and remains of blood vessels, collagen fibers, and osteocytes,” the authors of the study reported in the Journal of Vertebrate Paleontology this month. These features lent the fossil its status as a rare and remarkable specimen.
However, the osteocytes prompted the team to conduct a more detailed examination of the remains, particularly their properties as nuclei and, thus, their potential as a source for DNA. DNA is an essential molecule that supplies the instructions for living organisms to develop, live, and reproduce. It is passed on to all living descendants through the process of meiosis. Each strand of DNA is complementary to the other and contains a string of four different nitrogen bases—adenine, thymine, guanine, and cytosine—which serve as the letters that make up its code.
In addition to being able to identify the nuclei of the cells, the scientists found that the DNA was preserved similarly to other organic molecules discovered in fossils. It is this remarkable resiliency that makes this find so exciting.
Edwin Cadena, lead author of the study, explains that while it is not possible to determine the specific species from the incomplete remains of the turtle, it could be classified as belonging to the Lepidochelys genus, which includes modern Kemp’s ridley and olive ridley sea turtles. This is the oldest member of this genus that has been described to date. Cadena hopes that future investigations will involve sequencing small DNA fragments from the fossil, which may help shed light on the poorly understood evolutionary history of the Lepidochelys genus as a whole. (Earlier this year, researchers published the first sequence of Neanderthal DNA.) Molecular paleontology is an emerging field that attempts to infer broader conclusions about fossils through DNA remnants rather than the physical shapes of their bodies, which are more susceptible to decay.) Gizmodo reports.