Question about Ankylosauria, or at least Polacanthidae

[Jamie Stearns <stearns5@cox.net>]

This is something that's been bugging me for a while.

Generally, groups of dinosaurs tend to be based on which members of the 
group were named first; this is, I take it, why Saurornithoididae was 
renamed to Troodontidae anfter Stenonychosaurus and Troodon were found to be 
the same thing. This was confirmed when the thought of naming a clade 
"Deinonychosauria" for Troodontidae+Dromaeosauridae came up and it was 
remarked that it would more correctly be "Dromaeosauria" as Dromaeosaurus 
was named before Deinonychus (though it should actually be "Troodontia" as 
Troodon was named before either).

With that in mind, it should stand to reason that Polacanthidae should have 
been called Hylaeosauridae, and Ankylosauria possibly renamed Hylaeosauria, 
as Hylaeosaurus was named before either Polacanthus or Ankylosaurus was. I 
can understand why Ankylosauria would stay, as it more accurately describes 
the group's members, but at least Polacanthidae, going by naming priority, 
should be renamed after its first described member. Why wasn't it? I don't 
think Hylaeosaurus being relatively incomplete would have anything to do 
with it, as Ceratops isn't all that complete either and still has 
Ceratopsidae and Ceratopsia named after it...