Interpreting the past can be a difficult task. We’re relying on pieces of rock that are millions of years old and trying to determine which specific, unknown and possibly long-extinct organism did this in a particular way. It’s not unheard of for scientists to mix or confuse ancient fossils (sometimes with hindsight revealing surprising results). But a new article has revealed a case of mistaken identity that is too surprising to deny.

The fossil pictured above and a similar one were found in Colombia decades ago and were classified as a plant called . sphenophilum colombianum. Now scientists have determined that the fossils are not actually plants, but traces of the inside of a turtle shell.

They named the fossil they examined “Turtwig”, inspired by the Pokemon that is part turtle, part plant.

“We went to the fossil collection at the Universidad Nacional de Colombia in Bogotá and started looking at the plants, and as soon as we photographed them we thought, ‘This is amazing,'” says paleobotany expert Fabiani Herrera of the Field Museum. “If you look in detail, the lines you see on the fossil don’t look like the veins of a plant; I was sure it was probably bone.”

Fossils have always been a bit weird. They were discovered by a priest named Padre Gustavo Huertas, who collected rocks and fossils in the area near the town of Villa de Levia between the 1950s and 1970s. This collection included two fossils dating to the Early Cretaceous period, between 132 and 113 million years ago.

Huertas, who published a series of articles describing new plant species in the Cretaceous period based on the fossils he found, published a book in 2003 in which he described the species called Sphenophilum colombianum based on two fossils.

Even then, this statement raised an eyebrow or two: it was believed sphenophyllum It became extinct 100 million years ago and was not previously found in this part of the world. These inconsistencies caught the attention of paleobotanist Hector Palma-Castro of the National University of Colombia, and he and his colleagues decided to study the fossils in more detail.

When they discovered that the samples were closer to bone than leaves, they turned to paleontologist Edwin-Alberto Cadena of Universidad del Rosario, an expert in identifying ancient turtles.

“They sent me pictures and I said, ‘That sure looks like a shell,’ the bony upper shell of a turtle,” Kadena said. “I said, ‘This is great because it’s not just a turtle, it’s a hatchling, very, very small.’

However, the fossil did not have the typical markings found on the outside of a turtle shell. This seems to have contributed to his misidentification.

The markings on the fossil rather represent the vertebrae and ribs that form part of the turtle’s shell. They look a lot like the midrib and veins of a leaf; It’s easy to understand how Huertas could think this to be the case. As the turtle grows, these bones fuse together, so researchers can determine how old the turtle was when it died. They found that it was no longer a hatchling, but still a juvenile, less than a year old, and belonged to the sea turtle clade Panchelonioidea.

Because young turtles are very fragile, their remains are rarely found. Researchers believe Turtwig is likely related to Cretaceous sea turtles, which could grow up to 15 feet long, and could be an important clue to the mysterious life cycle of these ancient animals. Researchers say this, like many other discoveries, shows the value and importance of looking at fossil collections in museums and applying new knowledge to old bones.

“We have solved a small paleobotanical mystery, but more importantly this study demonstrates the need to re-examine historical collections in Colombia,” says Herrera.