The second species, P. blackfeetensis, is based on a specimen in the Museum of the Rockies (MOR 454), which was described by another notable paleontologist, Jack Horner.
Wyodrębnienie drugiego gatunku, P. blackfeetensis, bazuje na znalezisku należącym do Museum of the Rockies (MOR 454), opisanym przez innego znanego paleontologa, Jacka Hornera.