Pathological Microstructure of a Miocene Ostrich Eggshell from Asia

Struthio linxiaensis is the oldest fossil ostrich from Asia till today.This paper analyzes the microstructure of the eggshell of Struthio linxiaensis.The SEM and light microscopic results show that a pathological structure occurred associated with the formation of pore canal.The feature of this structure is that crystals of the columnar layer are around the lower part of the pore canal,and formed a broad structure.This structure unit contracts upwards more severely than the canal and looks like a"garlic",which was observed in amniotes eggshells for the first time.Many evidences indicate that this structure was deposited with the columns simultaneously.The radial section view suggests that the"garlic structure"is not a result of antiperistaltic waves in the avian oviduct.The most possible process of the"garlic structure"formation is the column units around the pore canals with imperfect acidifying when calcified,or have some correlations with the changes in the protein profiles of the organic matrix in the calcareous eggshell.