Complex sentence: The possibility that Japanese might be related to Dravidian was raised by Robert Caldwell (cf. Caldwell 1875:413) and more recently by Susumu Shiba, Akira Fujiwara, and Susumu Ōno (n.d., 2000).
Split into simpler sentences: The possibility that Japanese might be related to Dravidian was raised by Robert Caldwell (cf. Caldwell 1875:413). A relationship between Japanese and Dravidian has more recently been advocated by the Japanese scholars Susumu Shiba, Akira Fujiwara, and Susumu Ōno (n.d., 2000).