Quaternary fossil horses within Prados-Guatén Depression (Pantoja de La Sagra, Toledo)

Abstract

During the first field-meeting of the Madrid Quaternary Research Group (GQM-AEQUA) several fossil teeth remnants of horses were localised at the ancient sand-quarries of Pantoja de La Sagra (Toledo), which presently are abandoned and refilling in progress. The possibility of deterioration and loss of the localised fossils remnants induced by the quarry works, they were collected and taken away to the Museo Nacional de Ciencias Naturales (CSIC, Madrid) for their preservation and analysis. Fossil remains correspond to a left maxilla with two in situ molars, another one inset on its alveolar cavity, fragments of premolar cavities, as well as other seven more isolated teeth. These fossils were outcropping in a sandy level at four meters below the +15 m fluvial terrace surface of the axial sector of de Prados-Guatén Depression, which is considered the last fluvial level belonging to the ancient Manzanares-Guatén fluvial system during the Lower-Middle Pleistocene transit (Silva, 1988). In detail, the upper fluvial sediments of this particular terrace level were interpreted as the result of the overlapping between the last materials deposited by the ancient Manzanares-Guatén fluvial system and the first ones resulting from the readjustment of former tributaries after the abandonment of the Depression caused by fluvial capture of the Lower Manzanares Valley SW Madrid City. The morphological features of the oclusal surface of the horse teeth and morphometric comparative analyses indicate that they belong to the specie Equus ferus, and probably to the subspecie mosbachensis. However due to the bad definition of this group in Europe and the few individuals analysed the better classification is Equus ferus cf. mosbachensis. The bioestratigraphic distribution of this fossil horse group in Europe extends on the upper part of the Middle Pleistocene (c.a. 500-200 ka B.P.). Few lithic artefacts outcropped also associated to the fossil remains, constituted by laminar flakes of hard technological classification. Fossil remains analysed in this work joint to the unique previous quaternary fossil mammal described for the Prados-Guatén Depression constituted by Mammuthus meridionalis NESTI of the former quarry of Esquivias adjacent to the AVE railway line (Silva et al., 1988b; 1999). The chronostratigraphic attribution of the fossil horses (Upper Middle Pleistocene) described here indicate that fluvial sedimentary activity within the Depression was relevant after its abandonment. Ancient tributaries of the former Manzanares-Guatén fluvial system, feed by local-intrabasinal headwaters, reworked the previous sandy sediments triggering multiepisodic deposition during the upper part of the Middle Pleistocene, before the more recent eventual incision of present streams dissecting the Depression.