Not necessarily. A great deal of microevolutions are in the soft bits of creatures. Denser musculature, or thicker/thinner hair, or adaptations to the squishy bits that decompose. Not to mention that fossilization requires a very specific set of conditions to occur, so possibly those transversal bones occurred where/when the conditions were less than valid for fossilization. Also, Darwin's theory isn't the entirety of Evolution as a theory.