Exceptional coprolite association from the Early Cretaceous continental Lagerstätte of Las Hoyas, Cuenca, Spain

Abstract

Coprolites are some of the most abundant fossils at the Las Hoyas site, a well-known Early Cretaceous Konservat-Lagerstätte located in Cuenca, central Spain. The coprolite association is described, introducing taphonomic features and sedimentological properties. This study is based on a subsample of 433 fossils selected from some 2000 specimens collected. The taphonomic features of the coprolites show that their integrity, absence of desiccation marks, and volume are congruent with faeces produced and deposited in an aquatic ecosystem, which were immediately covered by microbial mats. The highest abundance of coprolites, 96%, occurs in layers linked to the presence of microbial mats. Consequently, it is likely that coprolites are taphonomically autochthonous. A dichotomous key has been made in order to delimit the morphotypes. The key is based on (1) presence/absence of spiral marks, (2) morphology of coprolite ends, including polarity, expansion, and surface, and (3) overall shape, outline, diameter, and constrictions. Twelve different morphotypes are distinguished: spiral, circular, irregular, elongated, rosary, ellipsoidal, cylinder, bump-headed lace, fir-tree, cone, straight lace, and thin lace. The association is dominated by thin-lace and cylinder morphotypes. The sizes, inclusions, and EDX analyses indicate that the Las Hoyas coprolites correspond mostly to carnivorous producers with ichthyophagous diets, as crocodiles, urodelans and different kind of fishes.