Elucidating anuran accumulations: massive taphocenosis of tree frog Hyla from the Chalcolithic of El Mirador cave (Sierra de Atapuerca, Spain)

Abstract

Anurans, such as frogs and toads, are occasionally very abundant in archaeo-paleontological sites and representing >80% of the remains. These accumulations have been linked mainly to human consumption in the European context, by the preferential selection of body parts and by the presence of burning, and to a lesser extent, cut marks (as in Chalain 3, Baume d’Ogens, Kutná Hora-Denemark). However, there are also records of accumulations attributed to natural catastrophic events (Bois-Roche). This research presents a taphocenosis of microvertebrates of reduced dimensions (7.8 × 2.7 × 2.4 cm) containing 2526 bones, from El Mirador cave of Atapuerca (Burgos, Spain) contemporaneous to an adjacent Chalcolithic burial (ca. 4500 BP). The taxonomical study has identified at least 12 different taxa, which include one urodele, two anurans, seven squamates and two rodents. Tree frogs, Hyla gr. arborea (Hyla molleri), constitutes 84% of the assemblage. Quantitative and qualitative taphonomic analyses are focused on Hyla bones and show the presence of breakage and digestion marks associated with animal predation, albeit in low percentages and in light or moderate degrees. Due to its characteristics, El Mirador accumulation has been identified as a pellet accumulation produced by a medium-large owl (category 2). The nocturnal raptor hunted its preys during a wet period in spring, when the reproduction of the tree frogs occurs, showing a possible evidence of opportunistic predation on a seasonal resource. These findings help to understand the importance of anurans in the trophic chains of Prehistoric times, not only among human groups but also among non-human predators.