Palaeopathological Fish Bones from Phosphorites of the Lake Manyara Area, Northern Tanzania – Fossil Evidence of a Physiological Response to Survival in an Extreme Biocenosis

In Plio/Pleistocene phosphorites at Minjingu, 5 km east of Lake Manyara, northern Tanzania, hyperostotic fish bones (‘Tilly bones’) are preserved, which developed in a strongly alkaline, lacustrine environment. The palaeopathological addition of bony tissue to the normal skeleton of these fishes was analysed with a scanning electron microscope (SEM), in thin sections under ordinary and polarised light, in microradiographs, with epifluorescence microscopy and their fluorine content was determined. The development of these structures is probably correlated with the high content of fluorine in this exceptional environment and denotes a physiological survival strategy in this ancient biocenosis.