Context : Fossil galaxy groups are spatially extended X-ray sources with X-ray luminosities above L _ { X, \textrm { \scriptsize bol } } \geq 10 ^ { 42 } h _ { 50 } ^ { -2 } ergs s ^ { -1 } and a central elliptical galaxy dominating the optical , the second-brightest galaxy being at least 2 magnitudes fainter in the R band . Whether these systems are a distinct class of objects resulting from exceptional formation and evolution histories is still unclear , mainly due to the small number of objects studied so far , mostly lacking spectroscopy of group members for group membership confirmation and a detailed kinematical analysis . Aims : To complement the scarce sample of spectroscopically studied fossils down to their faint galaxy populations , the fossil candidate RX J1548.9+0851 ( z = 0.072 ) is studied in this work . Our results are compared with existing data from fossils in the literature . Methods : We use ESO VLT VIMOS multi-object spectroscopy to determine redshifts of the faint galaxy population and study the luminosity-weighted dynamics and luminosity function of the system . The full-spectrum fitting package ULySS is used to determine ages and metallicities of group members . VIMOS imaging data are used to study the morphology of the central elliptical . Results : We identify 40 group members spectroscopically within the central \sim 300 kpc of the system and find 31 additional redshifts from the literature , resulting in a total number of 54 spectroscopically confirmed group members within 1 Mpc . RX J1548.9+0851 is made up of two bright ellipticals in the central region with a magnitude gap of \Delta m _ { 1 , 2 } = 1.34 in the SDSS r ^ { \prime } band leaving the definition of RX J1548.9+0851 being a fossil to the assumption of the virial radius . We find a luminosity-weighted velocity dispersion of 568 km s ^ { -1 } and a mass of \sim 2.5 \times 10 ^ { 14 } M _ { \odot } for the system confirming previous studies that revealed fossils to be massive . An average mass-to-light ratio of M / L \sim 400 M _ { \odot } / L _ { \odot } is derived from the SDSS g ^ { \prime } , r ^ { \prime } , and i ^ { \prime } bands . The central elliptical is well-fit by a pure deVaucouleurs r ^ { 1 / 4 } law without a cD envelope . Symmetric shells are revealed along the major axis of the galaxy indicating a recent minor merger . RX J1548.9+0851 shows a steep , increasing luminosity function with a faint-end slope of \alpha = -1.4 \pm 0.1 . Satellite galaxies show a clear spatial segregation with respect to their stellar populations – objects with old stars are confined to an elongated , central distribution aligned with the major axis of the central elliptical . Conclusions : Although RX J1548.9+0851 shows similar properties compared to other fossils studied recently , it might not be a fossil at all , being dominated by 2 bright central ellipticals . Comparing RX J1548.9+0851 with scaling relations from ordinary poor groups and clusters confirm the idea that fossils might simply be normal clusters with the richness and optical luminosity of poor groups .