DNA remains found in six-million-year-old sea turtle • Earth.com

Scientists recently discovered traces of DNA within the fossilized remains of a sea turtle closely related to contemporary Kemp’s Ridley and Olive Ridley turtles dating back six million years.

The discovery is one of the rare cases in which genetic material has been identified in ancient vertebrate fossils. Published in thesis Journal of Vertebrate Paleontology.

Bone cells

A fossil discovered in 2015 off the Caribbean coast of Panama yielded well-preserved bone cells called osteocytes.

Although the fossil is incomplete, with a relatively intact carapace — the turtle’s shell — but no remaining skeleton, researchers estimate the turtle would have measured about a foot (30 cm) in length during its lifetime.

DNA residues

In some of these osteocytes, cell nuclei remained intact and responded to a specific chemical solution. This reaction allowed scientists to detect remnants of DNA essential to an organism’s growth and function, explained Edwin Cadena, a paleontologist at the Universidad del Rosario in Bogotá and the Smithsonian Tropical Research Institute.

„I want to point out that we didn’t extract DNA, we were only able to identify traces of DNA in the embryos,” Catena said.

The preservation of DNA in ancient remains is rare, but not unprecedented, with the discovery of DNA remnants dating back some two million years in some ancient specimens from Greenland.

The only vertebrates showing fossils and DNA remains older than the newly studied turtle belong to two dinosaurs – Tyrannosaurus, about 66 million years ago, and Brachyloposaurus, about 78 million years ago. DNA remains have also been reported in insects dating back tens of thousands of years.

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Evolutionary history

The turtle in question belongs to the genus Lepidochelys, which includes two of the seven extant sea turtle species – the Kemp’s Ridley, found primarily in the Gulf of Mexico, and the widespread Olive Ridley.

This fossil is important in shedding light on the evolutionary history of this species, which is often unclear.

Due to the incompleteness of the remains, the researchers did not identify the turtle by its species.

Biomolecular residues

„Each fossil and each fossil site has specific preservation conditions, which in some cases may favor the preservation of original biological remains such as proteins and DNA,” Catena said.

„Perhaps in the future, and with more studies like this one, we will sometimes be able to sequence very small pieces of DNA and infer things about their closest relatives or incorporate that information into a broader molecular evolutionary study.”

Ridley turtles

Ridley turtles, especially those of the genus Lepidochelys, are relatively little known compared to other sea turtles and have unique nesting habits.

There are two species in this genus: the Kemp’s ridley turtle (Lepidochelys kempi) and the olive ridley turtle (Lepidochelys olivacea).


Ridley turtles are among the smallest sea turtles, with adults typically weighing between 75 and 100 pounds.


Their carapace (upper shell) is broad and somewhat heart-shaped, usually olive-green in Kemp’s ridleys and gray-green in olive ridleys.


They have flippers with clawless tips that are suitable for swimming in open seas.

Habitat and distribution

Kemp’s Ridley is found primarily in the Gulf of Mexico and along the Atlantic coast of North America. These turtles prefer coastal habitats such as bays, estuaries and lagoons.

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The olive ridley is found in the tropical regions of the Pacific, Atlantic and Indian oceans. They are mostly found in open water, but migrate to coastal areas for nesting.


A notable behavior of Ridley turtles is the „aripada,” a mass nesting event where thousands of females come ashore at once to lay their eggs.

Olive Ridley turtles are particularly known for this behavior, with significant arid events occurring in places like Ostonal, Costa Rica.


Ridley turtles are omnivorous, eating a variety of food items including crabs, shrimp, molluscs, jellyfish, and occasionally algae and seaweed.

Security level

Both species of Ridley Tortoise are listed under the IUCN Red List. Kemp’s ridley is classified as endangered, with habitat loss, bycatch in fishing gear and climate change affecting their nesting sites.

The olive ridley is listed as vulnerable, facing threats such as illegal egg collection, bycatch and habitat destruction.

Defense efforts

Various conservation programs and legal protections exist to protect Ridley turtles:

  • Establishment of protected areas and wildlife sanctuaries.
  • Implementation of regulations and initiatives to reduce bycatch.
  • Engaging in public education and awareness campaigns.


Synchronized nesting events, or bouts, are critical to the species’ survival because it drowns out predators and ensures more hatchlings make it safely to sea.

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