Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:sagittatus, was originally described from carp from the Amur River basin in Russia (Kulakovskaya and Akhmerov 1965), later on it was also found in Caspian Sea Drainage (Demshin andDvoryadkin 1981) and Japan (Scholz et al. 2001).
Category: