  We reconsider constraints on Brans-Dicke theories arising from the
requirement of successful Big Bang Nucleosynthesis. Such constraints typically
arise by imposing that the universe be radiation-dominated at early times, and
therefore restricting the contribution that a Brans-Dicke scalar could make to
the energy budget of the universe. However, in this paper we show how the
dynamics of the Brans-Dicke scalar itself can mimic a portion of the radiation
contribution, thereby allowing successful nucleosynthesis with a sizable
contribution to the total cosmic energy density. This possibility significantly
relaxes the existing bounds on Brans-Dicke fields, and opens the door to new
possibilities for early universe cosmology. The necessary fine tunings required
by such an arrangement are identified and discussed.
