I want to know the answer to the following question:
What may have replaced the "hind wing" as the primary mode of aerial maneuverability?
All the background I'm provided with is that "Euornithes also included the first avialans to develop true pygostyle and a fully mobile fan of tail feathers, which may have replaced the "hind wing" as the primary mode of aerial maneuverability and braking in flight.". Is that enough to answer the question?
Answer: yes