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. rubricati; their size and dental morphology are very similar, both have an anterior cingulum in the lower molars, well-developed entolophid, and a metaloph, wich is either free or tends to fuse with the posteroloph. H.huerzeleri is synonimized with H. grivensis. Several authors suggested this synonymy already. Populations assigned to H. huerzeleri belong in some cases to H. rubricati, and in most cases to H. grivensis. All populations described previously as H. cf. huerzeleri belong to H. grivensis. The Sciuridae are a family of rodents with a morphologically stable dental pattern. Hardly any modifications take place during large periods of time, but sudden changes may cause the abrupt appearance and disappearance of species, such as Freudenthalia daamsi and Aragoxerus ignis. Se describen tres nuevas especies de Sciuridae fósiles en la fosa terciaria de CalatayudMontalbán: Atlantoxerus idubedensis, Spermophilinus besana, y Freudenthalia daamsi, esta ultima es la única especie del género Freudenthalia, descrito junto con Aragoxerus como géneros nuevos. La descripción de estas nuevas formas está en el contexto de una revision sistemática de las espécies fósiles de Sciuridae de la Fosa. Por ello se revisan adernas los géneros Heteroxerus, Atlantoxerus y Spermophilinus, dando como resultado que se pongan en sinonímia dos casos del género Heteroxerus: H. vireti con H. rubricati y H. huerzeleri con H. grivensis. Se crée un nuevo género Aragoxerus para la espécie A. ignis que anteriormente se incluía dentro del género Heteroxerus. La sucesión de los yacimientos con Sciuridae ensuperposición estratigráfica nos ha permitido hacer algunas precisiones a la bioestratigrafía de las áreas de Daroca y Calamocha establecida por autores anteriores.