Abstract

The fractures produced in the bones during the diagenetic stage are studied in this work. The bones selected were 114 Hipparion metapodials (46 metacarpals and 68 metatarsals) from several Spanish Cenozoic localities (most of them come from the Teruel Basin). Our criteria for this selection was that there is available a very wide range of samples. In addition Hipparion metapodials show very variable sizes and different morphologies (depending on being metacarpals or metatarsals), allowing us to test the influence of these factors on the fracturation models. The fractures that cross completely through the entire metapodial section are interpreted as diagenetic origin. The total number of fractures detected are 330, 128 of them are in the metacarpals and 202 fractures in the metatarsals; therefore the number of fractures per fossil is similar even though the bone type is different. Hipparion metapodials present fractures produced after their burial, characterized by: (1) clear, simple planes; (2) perpendicular outline to the longitudinal axis and inclination to the order of 70 degrees; (3) preferential distribution in determined bone areas (the greatest frequency is detected in three main areas: the centre of the bone and two sectors more or less symmetrically situated between the centre and the edges). The maximum frequency fracture areas allow us to suppose that some metapodials have been fractured while maintaining certain flexibility. Others respond in a different manner: symmetrical fractures to the central shaft point. The hypothesis that these fractures are due to the lithostatic load is coherent with the models of stress distributions based on fixed ends beam-uniform load over entire span. Using this model combined with the rest bone position data is going to be a tool to rebuild a part of the taphonomic history of the bones while buried.

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