But this new species was an evolutionary dead end, it has no modern descendants.
Hmm... I don't believe the article stated that fact outright. There are still millions and millions of years in-between the fossil records that are missing. Here is a quote from the end of the article: "Its anatomy suggests it was an ambush predator that lurked just above the bottom, snapping at any smaller fish that swam too close – like some anglerfish do today."
The article did mention an extinct species called "
elpistostegids". But what they do say is that this fossil doesn't "fit" in the current record. (discovered artifacts), so it implies some possible contradiction of currently held postulates in the field.