<==o Steatornithidae (rasvalinnut) [paraphyletic??]
   |--o †Preficinae
   |  |-- †Prefica nivea Olson, 1987 
   |  `--o †Paraprefica
   |     |-- †P. kelleri
   |     `-- †P. major
   `--o †Steatornithinae (nykyrasvakehrääjät; modern oilbirds)
      `--o Steatornis (rasvakehrääjät)
         |?- †S. sp.
         `-- S. caripensis (rasvakehrääjä; oilbird)

Reference(s):

Feduccia, A., 1996: The origin and evolution of birds.
–Yale University Press, New Haven and London, 1996, xii-420

Lokki, J., Jännes, H. & Nikander, P. J., 1992: Otavan lintutieto.
–Kustannusosakeyhtiö Otava, Helsinki, Finland, 1992, pp. 1-440
      Translated from: Perrins, C. M. (ed.), 1990: The Illustrated encyclopaedia of birds.
–Headline Book Publishing Plc., London, England, 1990

Olson, S. L., 1985: The fossil record of birds. 79-239.
in Farner, D., King, J. & Parkes, K. (eds.), 1985: Avian Biology. vol VIII.
–Academic Press, New York. 1985.