The Early Miocene muroids (Muroidea, Rodentia) of the Ribesalbes-Alcora Basin (Spain): A thriving haven during a time of migration

The Campisano Ravine in the Ribesalbes-Alcora Basin (Spain, Early Miocene, Biozone C, MN 4) yielded a diverse and abundant assemblage of muroids, comprising five distinct taxa, and nearly 700 remains. The assemblage yielded five muroid taxa: Megacricetodon primitivus, Democricetodon decipiens, Eumyarion weinfurteri, Melissiodon sp., and Muroidea indet. The most abundant taxa were M. primitivus and D. decipiens, with M. primitivus being the most prevalent in the oldest sites and D. decipiens in the most recent ones.

E. weinfurteri was exclusively identified in the FS 1, MAB 3, and MAB 5 sites of the most recent biozone (L. ellipticus, see Crespo et al. 2021). In contrast, Melissiodon sp. was confined to the BC - 1 and MAB - 3 sites. M. primitivus was present in all Iberian basins, whereas D. decipiens exhibited considerable variability, being recorded in the Ca biozone of the Calatayud-Montalbán Basin, the last part of the C biozone of the Vallès-Penedès Basin, and the Buñol site.

It can be hypothesised that the studied basin may be a factor in the distribution of this species across the regions in question. Eumyarion was present in the Vallès-Penedès Basin from the first part of the C biozone, subsequently migrating to the studied basin and appearing in the Cb biozone in the Calatayud-Montalbán and Buñol basins. Melissiodon was absent from the latter basin from the MN 3 biozone to the last part of the C biozone and from the MN 5 biozone in the Vallès-Penedès Basin.

The presence of muroid faunas in the Early Miocene suggests that the coastal Ribesalbes-Alcora Basin functioned as a transitional region between the forested areas of west and central Europe and the drier inner Iberian Peninsula basins.