And how is it that something looking similar to something else at an early stage of development *proves* or supports common descent? If a creature has a head and four appendages, it will look similar until it develops it's identifying characteristics but that certainly doesn't mean that it's an indication of a common ancestor as much as an indication of common shape.
see the in-thread discussion on this between myself and TASMANIANRED - gillslits and tail development and reabsorption in the human embryo certaily *suggests* common descent