A fossil first identified as a plant is actually a baby turtle

After spending millions of years encased in rock, fossils can sometimes look like a completely different living thing. A turtle fossil may even bear a striking resemblance to a plant. When a team of paleontologists and paleobotanists re-examined a plant fossil first described about 20 years ago, they discovered that it was actually a baby turtle fossil. The rediscovery is described in a study published Dec. 7 in the journal Electronic Paleontology.

[Related: This 6-million-year-old turtle shell still has some DNA.]

Colombian priest Padre Gustavo Huertas collected rocks and fossils near the town of Villa de Levia from the 1950s to the 1970s. Two of the specimens found by Padre Huertas were small, round rocks with lines on them that looked like leaves, so he classified them as a type of fossil plant. They were described by Huertas in 2003 as Sphenophyllum colombianum and date back to when dinosaurs roamed the Earth between 132 and 113 million years ago (early Cretaceous period).

The age of this fossil and where it was found piqued the interest of Fabiani Herrera, assistant curator of fossil plants at the Chicago Field Museum and paleobotanist at the National University of Colombia in Bogotá, Colombia, and his postdoctoral fellow, Hector Palma-Castro.

“I am neither an expert on turtles nor on paleovertebrates [expert]but my student Hector and I knew that this specimen was not a fossil leaf,” says Herrera PopSci. “Fossil leaves are usually preserved quite flat and don’t have a bone-like texture, so we were quite intrigued when we saw the fossil for the first time.”

At first glance, the fossils, which are about two inches in diameter, appeared to be rounded nodules with preserved leaves of the plant Sphenophyllum. Then they noticed that some key features weren’t quite right. They searched the university’s fossil collection for other plants to compare, and deciphering the shape and margin of the leaf in question was a challenge. The lines seen in the fossil didn’t look like plant veins, and Herrera and Palma-Castro thought it might be bone.

For help, Herrara turned to Edwin-Alberto Cadena, a colleague and paleontologist who specializes in turtles and other vertebrates at the Universidad del Rosario in Bogotá. Cadena examines photographs of the fossil and believes it looks like the upper shell of a turtle, called the carapace. He found out that not only was it a turtle, but a hatchling of one of the world’s oldest extinct turtle species that could grow up to 15 feet long.

“Given that the fossil hatchlings were found in the same rocks where one of the most complete and oldest Early Cretaceous sea turtles, known as Desmatochelys padillai, we believe these hatchlings may correspond to this extinct species,” says Cadena PopSci. “Desmatochelys padillai belongs to a group of sea turtles known as protostegids that inhabited the planet during the Cretaceous period and include some of the largest turtles to ever live on Earth.

[Related: Gigantic fossils hint at super-sized 7,000-pound sea turtle.]

Cadena and his student, Diego Combita-Romero of the National University of Colombia, further examined the specimens and compared them to fossilized turtle shells and modern shells.

“When we first saw the specimen, I was amazed because the fossil lacked the typical markings on the outside of a turtle’s shell,” Cómbita-Romero said in a statement. “It was a bit concave, like a bowl. At this point we realized that the visible part of the fossil was the other side of the shell, we were looking at the part of the shell that was inside the turtle.

To determine its age, they looked at the thickness of its shell and the spots where the animal’s ribs were fused together into hard bone. The turtle was probably between 0 and 1 year old at death and in the post-hatching stage with a slightly developed shell when it died. Cadena says it’s very rare to find hatchling fossil turtles because the bones in their shells are quite thin and can easily be destroyed over time.

The team does not blame Padre Huertas for the mistake, as the features he thought were leaves and stems were actually the modified ribs and vertebrae that make up the turtle’s shell. Cómbita-Romero and Palma-Castro named the specimens Turtwig after a Pokémon that is half turtle and half plant.

“In the Pokémon universe, you come across the concept of combining two or more elements, such as animals, machines, plants, etc. So when you have a fossil originally classified as a plant that turns out to be a baby turtle, several Pokemon immediately come to mind. In this case Turtwig, a baby turtle with a leaf attached to its head,” paleobotany postdoctoral researcher Palma-Castro said in a statement. “In paleontology, your imagination and your ability to be amazed are always put to the test. Discoveries like these are truly special because they not only expand our knowledge of the past, but also open a window to the diverse possibilities of what we can uncover.

The team hopes to conduct more research on these samples, including using micro-computed tomography to look at the finer details of the bone and anatomy. They also plan to search for new fossils preserved in these same spherical rocks and hopefully find better-preserved hatchlings and even completely intact skeletons.

“The general public is critical to the discovery of new fossils and meteorites in the US and Latin America,” Herrera says. “At the Field Museum, we get a lot of inquiries every year. The next time you find an interesting specimen and don’t know what it is, ask an expert! You could discover an exciting new species or rock from our planet’s history.”

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