First study of a shell pathology in the lineage of basal turtles Helochelydridae

Abstract Helochelydridae represents an abundant and diverse clade of basal terrestrial turtles (stem Testudines), known from the Late Jurassic to the Late Cretaceous of both Europe and North America. Despite their relatively well-documented fossil record, no pathology in a member of this lineage has been documented so far. This study presents the first documented case of a pathological condition in a helochelydrid turtle, Plastremys lata , observed in the shell of a relatively complete skeleton from the lower Albian deposits of the Spanish Santa María Quarry (Teruel Province). The lesion, located on the visceral surface of the left plastral bridge, consists of a well-defined osseous outgrowth with a central depression. The specimen was analyzed through both superficial macroscopic examination and computed tomography (CT) scanning to assess the internal structure of the anomaly. The lesion is identified as the result of a non-traumatic pathological process, potentially associated with an inflammatory bone response. This find expands the paleopathological record of Cretaceous turtles and provide new insights into the health and biological responses to environmental stressors in helochelydrids.