Food web reconstruction through isotopic compositions of fossil faeces: Insights into the ecology of a late Barremian freshwater ecosystem (Las Hoyas, Cuenca, Spain)

A total of 54 coprolites with different morphologies from the Konservat-Lagerstatte of Las Hoyas (upper Barremian, Cuenca, Spain) were analysed for stable isotopes (delta N-15 and (delta C-13(org)) to examine the food-web structure of this ancient wetland. The Las Hoyas wetland exhibited wetter and drier periods that indicated water table oscillations. Differences in the delta N-15 values of coprolites collected from wetter and drier facies were probably due to different baseline delta N-15 values during the dry periods (higher) compared to those of the wetter periods. The delta C-13(org) values indicated that aquatic food resources were the most commonly used by the animals from Las Hoyas. Assuming a Trophic Enrichment Factor (TEF) of + 2.5 parts per thousand, three trophic levels were established for the coprolite association. All the specimens of circular, ellipsoidal, elongated, and rosary morphotypes fell into the same trophic level, whereas other morphotypes (cylinder, irregular, and thin lace) exhibited a wide range of delta N-15 values and the highest % N concentrations. The covariation between delta N-15 and delta C-13(org) values describe a wide spectrum of values across the middle and upper part of the ecosystem's food web structure, suggesting that the Las Hoyas ecosystem hosted specialist feeders and omnivorous and/or opportunistic feeders, the latter being the majority. The variation of delta N-15 values within the specimens of some morphotypes showed that the larger coprolites do not exhibit any correspondence between the faecal size and delta N-15 values. (C) 2019 Elsevier Ltd. All rights reserved.