The first occurrence of “Plesiochelyidae” marine turtles in the Early Cretaceous of South America

UNLABELLED: Thalassochelydians represent one of the earliest radiations of coastal to marine-adapted turtles, spanning from the Jurassic to Cretaceous periods. This study describes Craspedochelys renzi sp. nov., a new thalassochelydian, "plesiochelyid" turtle from the Hauterivian stage of the Early Cretaceous in Colombia. It is the youngest and the only known record of " Plesiochelyidae' outside Europe. The holotype, housed at the Naturhistorisches Museum Basel, was rediscovered after over 60 years and includes a partial shell, hindlimb bones, and caudal vertebrae. C. renzi shares key traits with " Plesiochelyidae", including a V-shaped posterior plastral lobe lacking an anal notch; an indentation at the hypoplastra-xiphiplastra contact; an "intermediate" bone between neural 8 and suprapygal 1; a fully ossified carapace and bridge; and absence of carapacial fontanelles. Within " Plesiochelyidae", it is assigned to Craspedochelys by its broader carapace, with an estimated length/width ratio of 4.12 for left costal 4, similar to other species in the genus; a relatively shorter plastron; and wider hyoplastra. Geological evidence links the specimen to the Moina Formation, a shallow marine deposit from the Hauterivian. This discovery expands the genus' spatial and temporal range, underscoring its evolutionary and paleobiogeographic significance. It highlights the importance of museum collections in re-evaluating long-overlooked specimens, enriching our understanding of past biodiversity and turtle dispersal patterns.

SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s13358-025-00394-1.