Researchers from the Universidad del Rosario, the Universidad Nacional de Colombia, Smithsonian Tropical Research Institute, the Field Museum of Natural History and the University of Vienna have detected a compound consistent with DNA in a partially preserved carapace of a Lepidochelys turtle from the Late Miocene Chagres Formation of Panama. The specimen also represents the oldest fossil record of Lepidochelys turtles.
Cadena et al. found DNA traces in the 6-million-year-old carapace of a Lepidochelys turtle. Image credit: Edwin Cadena, Universidad del Rosario & STRI.
Currently, only seven species of sea turtles exist. Among them are two in the genus Lepidochelys: the olive ridley sea turtle (Lepidochelys olivacea) and the Kemp’s ridley sea turtle (Lepidochelys kempii).
Despite being among the most common sea turtles in much of the Caribbean Sea and elsewhere, little is known about their history or evolution.
The remains of a turtle shell recently found in the Chagres Formation on Panama’s Caribbean coast represent the oldest fossil evidence of these turtles ever found.
This ancient individual lived approximately 6 million years ago during the Late Miocene epoch, a time when the world was getting cooler and drier, with ice accumulating at the poles, sea levels falling and reduced rainfall.
“The specimen has rectangular, anteroposteriorly short pleural scutes, a characteristic shared with members of Lepidochelys,” said lead author Dr. Edwin Cadena and his colleagues.
“It is potentially closely related to Lepidochelys olivacea because it shares a similar number of pleurals, but its precise taxonomic status remains uncertain.”
In addition to finding the oldest record of Lepidochelys, the paleontologists discovered something unexpected in the fossil bones of this turtle: traces of DNA.
After detecting preserved bone cells (osteocytes) with nucleus-like structures, they used a solution called DAPI to test for the presence of the genetic material.
“Within the entire vertebrate fossil record on the planet, this had only been previously reported in two dinosaur fossils, including one of Tyrannosaurus rex,” Dr. Cadena said.
This discovery gives the fossil vertebrates preserved on the Caribbean coast of Panama enormous importance not only for understanding biodiversity at the time of the emergence of the Isthmus of Panama, which divided the Caribbean from the Pacific and joined North and South America, but also for understanding the preservation of soft tissues and possible original living matter such as proteins and DNA.
“Our data demonstrate the potential for DNA to persist in specimens that are both millions of years old and are from lower latitudes, which challenges traditional paradigms of biomolecular preservation,” the authors concluded.
The findings appear in the Journal of Vertebrate Paleontology.
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Edwin-Alberto Cadena et al. An Upper Miocene marine turtle from Panama that preserves osteocytes with potential DNA. Journal of Vertebrate Paleontology, published online September 28, 2023; doi: 10.1080/02724634.2023.2254356
