In an extraordinary scientific discovery, traces of DNA have been found in the fossilized remains of a sea turtle that lived around 6 million years ago. This significant find emphasizes the potential of uncovering genetic material from ancient vertebrate fossils, a feat previously thought to be extremely rare.
The ancient fossil, which bears close relation to the modern Kemp’s ridley and olive ridley turtles, was unearthed along the scenic Caribbean coast of Panama back in 2015. The fragmentary nature of the fossil offered a relatively complete carapace (the turtle’s protective shell) but did not provide much of the remaining skeletal structure. Estimates based on the fossil suggest that the turtle would have been approximately a foot (30 cm) in length during its lifetime.
What made this discovery even more remarkable was the pristine condition of some of the bone cells, known as osteocytes. Within these osteocytes, the nuclei were immaculately preserved. Upon being subjected to a specialized chemical solution, these cell nuclei displayed reactions indicative of the presence of DNA remnants. This DNA, the fundamental molecule responsible for an organism’s growth, development, and functioning, offers a fleeting glimpse into the world of ancient organisms.
Leading the study was paleontologist Edwin Cadena from Universidad del Rosario in Bogota and the Smithsonian Tropical Research Institute. Cadena emphasized the nature of their discovery by stating, “We did not extract DNA. Rather, we recognized the mere presence of DNA traces within the nuclei.”
DNA, being a delicate and perishable molecule, is challenging to find preserved in ancient remains. However, in ideal conditions, remnants of this molecular wonder can survive through the ages. In a recent discovery last year, for instance, DNA from plants, animals, and microorganisms, dating back to approximately 2 million years, was identified in sediment samples from the farthest reaches of Greenland.
To provide context to the rarity of this finding, Cadena highlighted that the only vertebrate fossils older than this sea turtle, with similar DNA remnants, were of the majestic Tyrannosaurus, which roamed our planet about 66 million years ago, and Brachylophosaurus, which lived roughly 78 million years ago. There have also been instances of DNA remnants found in insects dating back tens of millions of years.
The ancient turtle fossil belongs to the genus Lepidochelys. This genus is represented today by two of the world’s seven existing sea turtle species: the Kemp’s ridley, renowned as the world’s smallest sea turtle predominantly found in the Gulf of Mexico, and the olive ridley. The olive ridley is a near mirror image of its Kemp’s counterpart but has a more extensive distribution, mainly in the tropical waters of the Pacific, Indian, and Atlantic oceans.
Shedding light on the genus’s evolutionary journey, this fossil stands as the most ancient member of Lepidochelys ever discovered. However, due to the incomplete nature of the fossil, identifying it down to the species level was challenging.
Cadena expounded on the preservation dynamics, saying, “Every fossil and fossil site has unique preservation conditions. Some of these might favor the preservation of original biomolecules like proteins and DNA.”
Looking ahead, Cadena is optimistic. He envisions that future advancements and more research of this kind could potentially allow scientists to sequence tiny fragments of ancient DNA. Such achievements could revolutionize our understanding of these creatures and their close relatives, as well as provide invaluable data for broader molecular evolutionary studies.
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