Antigua presencia de Theodoxus sp. (Gastropoda: Neritidae) en el Tajo español: una evidencia arqueológica para la Edad Media

This study analyzes the discovery of Theodoxus sp. shells at the medieval archaeological site of Albalat (Extremadura, Spain), associated with direct (14C) and indirect dating (ceramic typologies, coins) to the 11th-12th centuries. The archaeological context suggests that the shells were accidentally incorporated into thesite, likely caught in the nets used to exploit the river’s fishing resources, which have also been documented at Albalat. Therefore, it demonstrates the ancient presence of populations of Theodoxus sp. in the Spanish section of the Tagus River, where they now seem to have become extinct. This extinction could be related to the implementation and development of wastewater evacuation systems in Madrid and its surroundings cities since the 1850s. This discharges still constitutes the main source of pollution in the Tagus River