It’s only a guess…
but given the odd and large gap between the upper and lower jaws of Paleoparadoxia (Fig. 1), together with the loss of all teeth between the anterior and posterior ones, that gap might have been filled with the genesis of baleen in this sister to the Mysticeti whales. Note the canine (orange) is here aligned with the maxilla, essentially out of service. The anterior teeth make ideal scoops. The posterior teeth are flat grinders. The jaws are broader than tall, providing a wide space for a larger tongue. The naris is dorsally placed, enabling Paleoparadoxia to remain submerged.
Better data just came out today on the geologically oldest Archaeopteryx #12, which I have updated here. The new data shifted the nesting by one node, to the base of the Scansoriopterygidae and thus it still remains very close to the ancestry of all living birds.