Two small, oval fossils thought to be prehistoric plants are actually the remains of baby marine turtles, researchers have revealed.
The fossils, found in rocks dating to between 132 and 113 million years ago, were discovered in Colombia in the middle of the 20th century by Padre Gustavo Huerta, a priest with a penchant for fossil plants.
Initially it was thought the fossils represented a species of sphenophyllum – an extinct plant related to modern “horsetails” – with leaves split into wedge shapes and veins radiating from their bases. But experts now say that was a mistake.
“During the re-examination of the fossils, we attempted to find the veins of leaves. However, what we observed was a delicate layer of spongy bone tissue, leading us to rule out the possibility that these fossils were from plants,” said Prof Edwin Cadena, a co-author of the study from the Universidad del Rosario in Bogotá.
“Instead, we began to compare them with fossils of vertebrates, and images of hatching turtles immediately came to our minds.”
The team say that revealed the oval fossils – which are 5cm and 6cm in length – are actually the hard shells, or carapaces, of marine turtles. What were originally thought to be the veins of leaves are actually bone growth patterns, they note, while there is also evidence of bones within the shell called neurals and costals, as well as highly serrated joints between them.
The researchers say the turtles were probably less than a year old, and possibly of the species Desmatochelys padillai. This was a type of protostegid, a group of extinct marine turtles that include some of the largest ever to have lived.
However, in a nod to the early misidentification the team have nicknamed them “Turtwig”, after a Pokémon character that is half-turtle and half-plant.
Dr Nick Fraser, an expert in vertebrate palaeontology at National Museums Scotland, who was not involved in the study, said the new interpretation made much more sense, as sphenophyllum existed in the Palaeozoic era, whereas the deposits the fossils were found in date from the later Mesozoic era – a disparity Cadena said was akin to erroneously suggesting dinosaurs lived at the same time as mammoths.
Fraser added: “In some ways, the new interpretation is no less important and their identity as hatchling turtles looks spot-on to me. Such early stage turtles are rare in the fossil record and additional study, including CT analysis, could reveal valuable information that might allow species [identification].”
Prof Andy Gale, a geologist and palaeontologist at the University of Portsmouth, said he was “absolutely sure” the specimens were hatchling turtles rather than a plant. “An unusual misidentification, which shows that you sometimes see what you want to see even if it’s not there,” he said.