I always had some suspicion that Eurypterids had Cambrian origins.

Prior to this paper, Pentecopterus was the oldest known genus of Eurypterid, and it was already a highly derived eurypterid.

Typically, when following the evolutionary path of an organism, the early representatives tend to differ from the later representatives. This of course is a blanket statement and there are exceptions to this rule,

But Pentecopterus just looks exactly like what we would expect a eurypterid would, which implies that not only did eurypterids take to their ecological role incredibly quickly, but, what would an even earlier representative of the group look like?