Abstract. Recent PHOBOS measurements of the excitation function for the pseudo-rapidity dependence of elliptic flow in Au+Au collisions at RHIC, have posed a significant theoretical challenge. We show here that these data are described by the Buda-Lund model. A universal scaling curve, predicted by the Buda-Lund hydro model, describes not only PHOBOS data, but also recent, detailed PHENIX and STAR elliptic flow data. This is a consequence of perfect fluid hydrodynamics as implemented in the Buda-Lund hydro model. [ 1, 2, 3, 4, 5]) reveal rich details in terms of its dependence on particle type, transverse (p T ) and longitudinal momentum (η) variables, and on the centrality and the bombarding energy of the collision. In the soft transverse momentum region (p T 2 GeV/c), the measurements at mid-rapidity are found to be reasonably well described by hydrodynamical models [ 6,7]. By contrast, differential measurement of the pseudo-rapidity dependence of elliptic flow v 2 (η), and its excitation function have resisted several attempts at a description in terms of hydrodynamical models (but see their new description by the SPHERIO model [ 8]). Here we show that these data are consistent with the theoretical and analytic predictions that are based on Eqs. (1-6) of Ref. [ 9], that is, on perfect fluid hydrodynamics.There is a confusion in the literature if perfect or perhaps an ideal fluid has