“Plant fossils” turn out to be baby turtles

“Plant fossils” turn out to be baby turtles

What was originally thought to be traces of plant structures are the remains of a shell about five centimeters in size. © Fabiany Herrera and Héctor Palma-Castro; drawing by Edwin-Alberto Cadena and Diego Cómbita-Romero.

Paleontological species mix-up story: Re-analysis of two alleged plant fossils has revealed their true identities. Instead of the leaf structures of a Cretaceous plant, these are the remains of the shells of baby turtles. In addition to clarifying the confusion, the fossils can now shed light on the early stages of development of the Cretaceous turtles, some of which were large, say the scientists.

As the Field Museum in Chicago reports, the unusual paleontological story goes back to discoveries made by the Colombian priest and researcher Padre Gustavo Huertas: In a fossil deposit near the town of Villa de Levya, he came across two stones about five centimeters in size that were attached to them flat side had line structures. After closer examination and comparisons with similar found materials, he came to the conclusion that these must be fossil plant structures. He assigned them to the Sphenophyllum group based on their characteristics. In 2003, Huertas then described the plant as Sphenophyllum colombianum.

What seemed surprising, however, was the age of the finds: they come from rocks that have been dated to 132 to 113 million years ago. However, other finds of representatives of the genus Sphenophyllum were at least 100 million years older. It was therefore assumed that this group of plants had long since disappeared in the Cretaceous period. The surprisingly young age and location of Sphenophyllum colombianum aroused the interest of paleobotanists Fabiany Herrera and Héctor Palma-Castro from the Field Museum. They decided to examine the fossils more closely and visited the fossil collection of the Colombian National University in Bogotá.

Are these really leaf structures?

At first glance, the previous classification was confirmed: they appeared to be nodular structures that had preserved the leaves of a Sphenophyllum plant. But upon closer analysis, Herrera and Palma-Castro noticed details that didn't add up. “It proved difficult to decipher the shape and edge of the leaf,” says Palma-Castro. Herrera then suspected that the structures might not be plant leaf veins, but rather bony structures.

So the two finally sought advice from another colleague: the paleontologist Edwin-Alberto Cadena from the Rosario University in Bogotá. “When I saw the photos, I immediately thought of a turtle’s shell,” says the scientist. But when he looked at the scale, he was amazed. “It’s very, very small,” Cadena said. Together with his colleague Diego Cómbita-Romero from the Colombian National University, he then investigated the mystery further: They analyzed the two fossils in more detail and compared the structures with the shells of both fossil and modern turtles.

Bones and shell parts instead of stems and leaves

They were finally able to clearly prove that the visible structures of the fossils do not represent plant structures. Instead, they are the insides of the shells of baby turtles. From then on, the researchers nicknamed the fossils “Turtwig” after a Japanese fantasy creature from the Pokémon series: a small turtle with a plant growing on its head.

Based on the characteristics of the structures, the researchers were also able to estimate how old the animals were at the time of their death: it became clear that the shells were only poorly developed. "This suggests that the turtles probably died when they were less than a year old - in the first instar after hatching," says Cómbita-Romero. As Cadena emphasizes, the fossils are something very special: “It is very rare that young fossil turtles are found because their delicate structures were easily destroyed.”

This means that the supposed paleobotanical discovery has now been transformed into an interesting paleozoological find. “These turtles were probably relatives of the Cretaceous turtles, which grew to almost five meters in length. But we still know little about how they grew to such sizes,” says Cadena. Finally, Herrera says of the unusual story: “We have solved a small paleobotanical-paleontological puzzle, but more importantly, this study shows how important it can be to re-examine finds,” says the scientist.

Source: Field Museum

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