The brief tenure of Gersson Rosas in the Dallas Mavericks' front office is over. Sources close to the situation told that the Mavericks and Rosas parted company Tuesday on the eve of Dallas' season opener against Atlanta, just more than three months after Rosas was hired away from the Rockets' front office. The reasons for the abrupt parting, sources said, are not immediately known. The Mavericks hired Rosas in July to bring a new voice to the front-office team spearheaded by longtime president of basketball operations Donnie Nelson and Keith Grant, whose association with the franchise dates to Dallas' inaugural season in 1980-81. Rosas, 35, worked his way from an intern to executive vice president of basketball operations in Houston and was one of three members of the Rockets' front office to be poached by other teams during the offseason. A native of Colombia, Rosas was initially targeted by the Mavericks to bolster their pro and college scouting efforts after working extensively with the Rockets' successful D-League franchise.