'Rashi': They were the Roshei Avos when lineage was recorded in the days of Yosam and Yarav'am (17). Malbim - "ha'Rosh" in the previous verse applies also to Yanai and Shafat, and also to "l'Veis Avosam" in this verse. Seven heads are listed here, for there were seven families of Gad in Vayigash and Pinchas.