Image of a tortoise Testudo hermanni by E. Razzetti

Researchers at the ICP have diagnosed for the first time details of the morphology of Testudo lunellensis, the fossil tortoise discovered in the paleontological site of Cova de Gràcia, during the construction of Park Güell in Barcelona. The research published in the magazine Amphibia-Reptilia shows the phenotypic plasticity of turtles and questions the classification of extant species.

Fossil remains of Testudo lunellensis studied in this work. Massimo Delfino. ICP

In this work, published by Amphibia-Reptilia, the ICP researchers describe for the first time the morphology of this species and they identify its characteristic traits, among which the tall peripheral bones and a peculiar form of the anterior lobe of the plastron, the underside of a turtle shell. The study identifies traits  in T. lunellensis characteristic of both T. hermanni, and T. graeca, T. kleinmanni and T. marginata, all of them different species of extant chelonians. This means that if the tortoise of the Parc Güell was still alive and we would classify it only from the morphological features we use to classify extant turtles, then T. lunellensis would superficially resemble the extant Testudo hermanni but a detailed study would unveil characters belonging to different species. Such mixture of characters in a Pleistocene tortoise further underlines the phenotipic plasticity of these organisms and strengthens the idea that we should focus on both morphological and molecular data in order to fully comprehend the phylogenetic relationships among extant and extinct taxa.

"The findings of the new paper by Delfino and colleagues teach us that morphology alone tells only part of the evolutionary history. Of many extinct species, only fossil evidence is available. True land tortoises are a remarkable exception, making them a test case for cross-examining morphological character evolution, and homoplasy, against phylogenies suggested by DNA sequence variation. The results of this important paper argue for caution with defining shared derived characters based on morphological characters prone to homoplasy" says professor Uwe Fritz, international expert in chelonians at the Museum of Zoology in Dresden. Homoplasy happens by convergent or parallel evolution, ie when a character is shared by a set of species, but is not present in their common ancestor.

The paleontological site of Cova de Gràcia was discovered and excavated in the late nineteenth century, during the construction of the Park Guell, designed by architect Antoni Gaudi. The fossil remains of tortoises that were found there are deposited in three Catalan museums: the Museum of the ICP in Sabadell, the Natural History Museum of Barcelona and the Geological Museum of the Seminary again in Barcelona. This site dates from the Middle Pleistocene, about 600,000 years ago, and T. lunellensis is therefore the youngest extinct species of Testudo. Jaume Almera, founder of the Museu del Geològic del Seminari, and Artur Bofill studied and published several works based on the remains recovered in Cova de Gràcia.