The Gemara begins by enquiring the source of the opening statement of the Mishnah, and challenging the choice of language used by the Tana who beging with ‘meimasai’ (from what time do we recite Shema) without first teaching us anything about this obligation.  The Gemara concludes that it is derived from the passuk ‘uveshachbecha uvekumecha’.  Why should we expect this Mishnah to be different from everywhere else in Mishnah where the Tana never discusses the basic Halachos and their sources, but rather comes to elaborate and expand on what is already known from the Torah (see Ramba”m Pirush Mishmayos Brachos who states that the Mishnah will never discuss basic halachos found openly in the Torah)?