Great coin! I was just reading about these...
From McMillan's Encyclopedic Dictionary
: "An early Islamic coinage of brief duration, which borrowed its designs, weights, and legends from contemporary issues of the Byzantine Empire." Also, describes these reverses so: 'the offending Christian cross was replaced with a globe on a pole' (the cross being the one on the steps you mention) and these retained the prior Bysantine obverses until new coinage was finally designed (shortly before 700 in most places and a bit after that in Spain and North Africa).
Arab-Sassanian coinage is along the same lines, although they are harder to tell apart from their pure Sassanian predecessors because they only added small Arabic inscriptions here and there to the designs. Apparently they were very much a people in a hurry - too many places to conquer and not enough time to design coins!
I love the history aspect of coins like this. Thanks for showing the book, too! Another for the wish list..