CRANIOFACIAL ONTOGENY IN CENTROSAURINE DINOSAURS (ORNITHISCHIA, CERATOPSIDAE) - TAXONOMIC AND BEHAVIORAL-IMPLICATIONS

Centrosaurine ceratopsians are characterized by well developed nasal h orncores or bosses, relatively abbreviated supraorbital horncores or b osses, and adorned parietosquamosal frills. Recent study of several pa ucispecific (low diversity) bonebed assemblages in Alberta and Montana has contributed greatly to our understanding of ontogenetic and taxon omic variation in the skulls of centrosaurines. Relative age determina tion of centrosaurines is now possible through examination of ontogene tic change ill several characters, including the surface bone morpholo gy of specific skeletal elements. The within-group taxonomy of centros auriues, is based almost entirely on characters of the skull roof rela ting particularly to horns and frills. Juvenile and sub-adult centrosa urines are characterized by relatively simple? unadorned skulls compar ed to their adult counterparts. As in numerous living taxa, the crania l ornaments of centrosaurines developed late in ontogeny, as individua ls approached or attained adult size. An important implication arising directly from this study is that juvenile and sub-adult centrosaurine s are difficult to distinguish taxonomically at the specific level. Tw o monospecific genera represented only by immature materials, Brachyce ratops montanensis and Monoclonius crassus cannot be defended and shou ld be considered nomina dubia. The late ontogenetic development and di verse taxonomic variation of horn and frill morphologies support the c ontention that these structures are best interpreted as reproductive c haracters employed in mate competition. (C) 1997 The Linnean Society o f London.