The paper announces, in charmingly thick academese:
The titanic baleen whales (Cetacea, Mysticeti) have a bizarre skull morphology, including an elastic mandibular symphysis, which permits dynamic oral cavity expansion during bulk feeding. How this key innovation evolved from the sutured symphysis of archaeocetes has remained unclear.
What the author, Fitzgerald, means is this: baleen whales have weird heads. How did they evolve from the less-weird heads of ancestral whales?

Then he writes about a new whale fossil, an intermediate step in head weirdness. The extinct Janjucetus hunderi had a very wide rostrum, or upper jaw, but had not yet developed the vastly expandable lower jaw of modern baleen whales.

He thinks this wide rostrum was a trick to improve suction feeding (slurping a whole squid or fish into the mouth) which was later co-opted for baleen feeding (taking a mouthful of water and then filtering out the edible plankton).

Sure, it's only tangentially related to squid, but whale evolution is cool! Check out this neat figure from the paper: