Trophic flexibility within the oldest Cervidae lineage to persist through the Miocene Climatic Optimum

The oldest known Cervidae lineage, Procervulus , is a useful example for understanding the adaptations of mammalian clades to climatic and environmental changes. It appeared in the Lower Miocene (MN3), persisted through the Miocene Climatic Optimum, and became extinct at the onset of the Mid-Miocene general cooling. A combined approach of dental microwear and mesowear is undertaken to reconstruct its feeding behaviour to learn whether and how it responded to new environmental circumstances. None of the Early and Middle Miocene fossil taxa in the Calatayud–Daroca and Rubielos de Mora basins (NE Spain) had a wholly browser or grazer lifestyle, but rather dietary strategies equaling those of extant mixed feeders. However, members of Procervulus were sensitive to changes in the structure of ecosystems and vegetation that occurred during the Middle Miocene, and responded to these by substantially increasing the intake of grasses and abrasives. Despite this, it did not apparently display the sufficiently high trophic flexibility to bring about a change in its feeding style. Two possible, probably interrelated, causes can be pointed out; constraints imposed by both its small body size and its brachydont cheek teeth. If such a change in the feeding style was crucial for its survival, Procervulus disappeared as a consequence of an insufficient response to environmental changes because it may have been unable to compensate for the low nutritional content and abrasiveness of the new food items over a prolonged period. As the last Procervulus and the first bovids in the basin have similar dental wear signals, competition could be another possible explanation for its disappearance. Middle Miocene Procervulus could have been at a clear disadvantage after the advent of Tethytragus , whose teeth present morphologies that suggest better adaptation to grass-eating. Since diets tend to reflect habitats, the wear signals and assignments obtained from the Ramblian and earliest Aragonian cervids are indicative of humid climates and mixed environments, where closed areas were well developed and browse vegetation was abundant. In contrast, data from late Early and Middle Aragonian cervids and bovids reflect dry-seasonal and more open scenarios, with a higher diversity of grasses and abrasives.