 "C. rara" and "C. petra" were considered almost identical, and found in the same environments (the Lance and Frenchman formations), but differed in size, with "C. petra" smaller than "C. rara".In a 2009 review, Nicholas Longrich synonymized them as the same species, dismissing the size difference as possibly based on gender or growth stage.However, Longrich reversed his position following a 2011 analysis of Lancian birds, in which he and co-authors considered all four named species to be distinct.