Comparative osteology of Chondrostoma orientale and C. nasus

. Comparison of morphological structures is a key element in evolutionary biology and taxonomy, as well as in the studies concerning variation and biodiversity either at interspecific or intraspecific levels. This study aimed to compare the bony structures of Chondrostoma orientale and C . nasus . For this purpose, three specimens of C. orientale from the Kor River (passing through Iran), and five specimens of C. nasus from the Danube (passing through Germany, Austria, Slovakia, Hungary, Croatia, Serbia, Romania, Bulgaria, Moldova and Ukraine), Dnieper (passing through Russia, Belarus and Ukraine) and Rhône river basins (passing through Switzerland and France), as well as Lake Ohrid (Located between Macedonia and Albania) were analysed. The results showed that the two anterior lateral processes of supraethmoid bone were more distant in C. orientale than those in C. nasus . The anterior profile of the supraetmoid bone was concave in C. orientale , while it was almost flat in C. nasus . The posterior pharyngeal process in the basioccipital was wide and triangular in C. orientale and narrow and rectangular in C. nasus . The maxillary mid-lateral ascending process was slightly inclined forward in C. orientale , while it was slightly inclined backward in C. nasus . The maxillary distal process was long in C. orientale and it was short in C. nasus . The premaxillary had a rostral ascending process in C. orientale , while it was missing in C. nasus . The anterior portion of the dentary was narrow and elongated in C. orientale and the coronoid process was perpendicular and located in the middle of the dentary; in contrast, the anterior portion of the dentary was short and wide in C. nasus and the coronoid process was inclined forward.