Tafonomía y paleoecología del ecosistema acuático de Las Hoyas (Barremiense superior, Serranía de Cuenca).

Abstract

The freshwater ecosystem of Las Hoyas contains one of the most significant records of aquatic organisms described from the Early Cretaceous worldwide. The benthos was formed by a diverse assemblage of animals such as aquatic insects, ostracods, cray-fishes, and juvenile and small adult fishes, which depended on the ground cover of charophytes and aquatic angiosperms for shelter and food. The nekton was mainly composed o f crustaceans and a large variety of fishes. Phytoplankton is represented by two chlorophytes and zooplankton is represented by planktonic pupae of dipterans. Cheirolepidiaceous conifers, matoniaceous tree-ferns and herbaceous schizaeacean ferns were growing in swamps. Among tetrapods with aquatic habitats modern amphibians and reptiles were found. In spite of the exceptional preservation, the fossil record of Las Hoyas includes sedimentological, taphonomic and palaeoecological biases. Form the palaeoecological point o f view, mass mortality levels contain thousands of individuals of crayfish associated with freshwater plant remains. These levels are attributed to eutrophication events of the otherwise oligotrophic lake. Other mass-mortality levels include hundreds of juvenile teleostean individuals associated with small shrimps. Changes in the water-table and related temperature changes, variation of acidity or input of toxic substances may account for this type of mass mortality.