Revisión de los Sciuridae del Aragoniense y del Rambliense en la fosa de Calatayud-Montalbán = Revision of Aragonian and Ramblian Sciuridae in the Calatayud-Montalban Trench

The Sciuridae are the family of rodents that comprises all extant and fossil squirrels. In the Ramblian and especially in the Aragonian of the Tertiary basin of Calatayud-Montalbán (Aragón, Spain) the remains of Sciuridae are relatively abundant. A major problem solved in this paper is the distinction of Ml and M2, both in the upper and the lower dentition. Traditionally, in the literature these elements are treated as a unit Ml,2. We managed to separate them, on the basis of the study of material of two extant species, Atlantoxerus getulus and Sciurus vulgaris. In our study of the fossil Sciuridae from the Calatayud-Montalbán Basin 9 species were recognized, belonging to 6 genera: Heteroxerus rubricati, H. grivensis, Atlantoxerus idubedensis sp. nov., A. blacki, Aragoxerus ignis, Spermophilinus besana sp. nov., S. bredai, Freudenthalia daamsi sp. nov. y Palaeosciurus feignouxi. Aragoxerus and Freudenthalia are new genera. Atlantoxerus idubedensis sp. nov. is a small Atlantoxerus, similar to primitive Heteroxerus, and characterized by a reduced or absent anterior cingulum in M1, M2 and M3. Spermophilinus besana sp. nov. is the smallest Spermophilinus species known so far. In the lower teeth the anterolophid is separated from the protoconid by a deep furrow, and the entoconid is reduced or absent. Aragoxerus gen. nov. (tribe Xerini) contains only one species, A. ignis, formerly assigned to Heteroxerus. Although Aragoxerus is quite similar to Heteroxerus, its smaller size, simple dental pattern, absence of metaconule and anterior cingulum, and the lack of accessory ornamentations permit us to distinguish it as a separate genus. Freudenthalia gen. nov. is a monospecific genus of uncertain systematic position, tentatively placed in the tribe Sciurini. Freudenthalia daamsi sp. nov. is the only species of this genus. It is characterized by a metaloph completely fused to the protocone, a loop-shaped metaconule, and the absence of the entolophid. Within the genus Heteroxerus two pairs of names are synonimized: H. vireti is a synonym of H. ru