The molecular developmental data provide a transition series in the evolution of feathers and feather branched complexity that is based entirely on the molecular developmental experiments.
To mention a few, chromium, manganese, iron, cobalt, and nickel are found in the transition series.
All elements of the transition series are part of a trimembrate apparatus of geniculate elements, two of which are modified tertiopedate, and the third is alate.
A complete morphological transition series appears to exist from forms with no flanking rows to those with a single parapet, to those with two complete, symmetrical parapets.
In this paper, the authors compiled a table comparing 34 different features of 10 different organisms on their supposed transition series from fish to tetrapod.