Archosauria: Avemetatarsalia to Neornithes
2° Nominal Author
Pachycephalosaurini is a family-group name first used by Sullivan (2000:198). Sullivan attempted to constuct an “apomorphy-based” definition but failed to include an internal specifier (“pachycephalosaurids with nodes in large clusters on squamosals (hypernoded forms) and nasals”). This is potentially a useful clade, including the largest species of pachycephalosurians in western North America, a group that may well become more diversified over time. A node-based definition is proposed here based on the two best known species.
Inactive Taxon Status
Current Age Range
Maastrichtian (71 Ma)
Maastrichtian (66 Ma)
Basis for Range
The earliest and latest records of the Pachycephalosaurini are from Maastrichtian-age rocks in Asia and western North America (Maryanska et al. 2004). Dates are rounded to the nearest million, the earliest from the beginning of the stage and the latest from the end of the stage (Gradstein et al. 2004).