Early Miocene herpetofauna from the Ribesalbes-Alcora basin (Castelló, eastern Spain): a first step toward modern herpetofaunas in the Iberian Peninsula

The Early Miocene is a key period in the evolution of modern reptile and amphibian faunas, particularly for snakes. However, there are very few studies focused on herpetofauna in Iberian sites of this chronology. In the present work, we studied the palaeoherpetofauna from 32 sites in the Ribesalbes-Alcora Basin, which has been dated to the Early Aragonian age (MN4, Early Miocene) based on its small mammal faunas. The studied remains from these sites have been attributed to 26 taxa, with a relatively consistent faunal composition throughout the sequence. Although the assemblages are composed of taxa typical of the Early Miocene, two taxa may indicate some peculiarities in the faunal composition. The described remains of Chalcides sp. lack expanded crown teeth, which may be related to a probable morphotype distinct from those recovered from localities in Central and Eastern Europe and Asia. The possible presence of Pyrenasaurus in CBR1 is striking. This genus was previously known only from the Late Eocene, so its identification here suggests it survived the Grande Coupure and points to ecological stability in the region.

Using the Habitat-Environment Gradient (HEG) method on the best-sampled localities, the estimated mean annual precipitation (MAP) values exceed current regional levels in all sites, except just one case. Our results point to fluctuations in humidity throughout the sequence, with alternating “humid” and “dry” phases. This cyclical pattern has been previously documented in palaeoenvironmental data derived from small mammal assemblages.