In a 1999 cladistic study of tapiromorphs , Luke Holbrook found indricotheres to be outside the hyracodontid clade .
In a 1999 cladistic study of tapiromorphs , Luke Holbrook wrote that they may not be a monophyletic ( natural ) grouping .
In a 1999 cladistic study of tapiromorphs , Luke Holbrook found indricotheres to be outside the hyracodontid clade , and wrote that they may not be a monophyletic ( natural ) grouping .