Paleobiological implications of Campanian coprolites

Abstract

Vertebrate coprolites (153 samples) in association with vertebrate and plant remains in the Upper Cretaceous (Campanian) sediments of the Cerro del Pueblo Formation, in southeastern Coahuila, Mexico, represent at least ten morphotypes, ranging from ca. 1 cm to 3 cm. At least one suggests a carnivore origin due to the presence of abundant bone fragments, but most of the coprolite morphotypes were produced by either omnivores or herbivores. Analysis of inclusions of the coprolites revealed plant remains, such as stems and isolated vascular elements, and papillate and non-papillate cuticles. Two seed types have been recognized within two coprolite morphotypes. The first one has lythraceous affinity, being comparable to members of a morphological complex within Nesaeeae. The second seed type, which shows adaptations for water dispersal, belongs to Ranunculaceae, and is described as Eocaltha zoophila gen. et sp. nov. Although Eocaltha evolved a mechanism for abiotic dispersal, the seeds were apparently occasionally ingested by a vertebrate. The presence of seeds of E. zoophila in a coprolite suggests that the organism that produced it was looking for a high-quality diet perhaps represented by the seeds, and served indirectly as a biotic seed dispersal agent. The combination of abiotic and biotic dispersal syndromes, plus the fact that the seeds appear to be scarified suggest a case of diffuse coevolution. Interactions, as herbivory, during the Cretaceous prompted biotic dispersal of angiosperm diaspores as revealed by the presence of seeds of E. zoophila.