An improvement of this: A Completely Different Kind of Reef Which I couldn't delete because it already had answers, and deleting an answered question will dock me some reputation.
Today's reefs are built primarily by Anthozoa, the corals and sea anemones. Alongside them are Porifera, the sponges, and Crinoidea, the sea lilies. But in this scenario, the corals, anemones, sponges and crinoids have been extinct for 65 million years, leaving the role of reefbuilders to go to the following:
If our 21st-century aquatic reefs consist only of the listed animals, would they be more extensive and common than the coral reefs? Or will they still be limited to the tropical shallows?