Análisis tafonómico de los yacimientos de Somosaguas (Mioceno medio, Madrid)

Abstract

The taphonomy of two overlain vertebrate fossil sites from the Madrid Miocene basin is analysed. The bone sample from Somosaguas North shows an unusual mixed preservation states in fossil mammal assemblages, with: 1) some delicate bones with intact surfaces; 2) thousands of bone fragments, most of them preserving histological microstructures and remains of invasive microfilaments; 3) some abraded, rounded elements; 4) decayed bones forming a dusty mass; and 5) bones partially o totally replaced by a secondary mineral substance. Most long bones show a preferred orientation in N-S direction. These diverse elements are concentrated in a debris-flow type of sediment, formed by a process of mass-transport with a mixed assemblage of heterogeneous fossil remains and gravel-sized pebbles floating on a dense, viscous sediment. The spatial coincidence with the older fossil site Somosaguas South, similar to Somosaguas North but with smaller sizes and less erosion effects, may be due to the neighbouring of an ancient water pond in the Miocene arid landscape of Madrid. The high proportion of juvenile bones suggests a seasonal mortality during drought periods.