Monoclonius lowei Sternberg 1940

Holotype CMN 8790

The genus Monoclonius was first described by Charles Sternberg in 1940 based on a skull collected from southeast of Manyberries, Alberta. Subsequently any centrosaurine cranial material found lacking diagnostic ornamentation was referred to this taxon.  Monoclonius lowei was declared a nomen nudum by Scott Sampson et al. (1997) because the type material lacked adult characters that could be used to assign it to a recognized taxon.  Alison Tumarkin and Peter Dodson (1998) used a heterochronic argument to support the validity of the genus, based on the holotype skull of Monoclonius lowei (NMC 8790) from the Dinosaur Park Formation of southern Alberta.  They argued that because the length the midline parietal bar of this specimen is the longest known for the Centrosaurinae (at 609 mm it is 9.0% longer that the next longest parietal bar [545 mm; Centrosaurus apertus NMC 5429], M. lowei is an example of a paedomorphic taxon and that its subadult characters are really adult characters.  The type skull is presently being studied by Ryan, Tumarkin, and Dodson.

Image from Sternberg, C.M. 1940. Ceratopsidae from Alberta. Journal of Paleontology 14: 468-480.