But that half-open beak isn't the most usual thing...
Anyway, the early art of Marco Gervasio is FULL of this. At one point, he copied an entire sequence of panels (somewhat altered) from a Cavazzano story, he also used a picture of the desert outside Duckburg (!) by Freccero (only mirrored/flipped), and various expressions/poses from Mastantuono. It didn't help that he used contemporary stories that had often only been released a few months earlier (which points to the time issue). Thankfully he got more fluid over the years and developed his own style.