Morrison Formation turtle tracks question

[Saint Abyssal <saint_abyssal@yahoo.com>]

I've been reading John Foster's "Jurassic West" about the Morrison, and in the 
chapter on trace fossils Foster talks about the formation's few turtle 
trackways being classified in the ichnogenus Chelonipus, yet on the next page 
the diagram of the tracks refers them to Chelonichnium. Does anyone know which 
it is? Or both?

The text sort of obliquely implies that the tracks may have actually been 
REclassified into Chelonipus from an unnamed ichnogenus. Presumably they could 
have been reclassified from Chelonichnium, but I'm loathe to try to guess at 
what the author wanted to say, since I lack any expertise.

Does anyone have any knowledge or good references discussing Morrison turtle 
trace fossils?

~ Abyssal