Variability of hinge structure in Sarmation Mactridae from Borisphenian Gulf

Changes in the dentition of Mactra species from the Sarmatian of the Borisphenian Gulf are related to changes in the salinity of the waters. With increasing fresh water, the upper lateral teeth on the right valve become weaker and the lower more pronounced, and the dental plates of Tooth 2 on the left valve become closer and intergrade. With increased salinity, the opposite morphologic changes occur. The variability of hinge characteristics increases with an increase of fresh water, and decreases with increasing salinity. The entire molluscan fauna changes in the section, reflecting changes in the salinity. The salinity changes are related to climatic changes, documented by paleobotanical evidence from surrounding areas.—T. G. Gibson