Turanoceratops tardabilis—sister taxon, but not a ceratopsid

Abstract

The ceratopsian dinosaur Turanoceratops tardabilis, from the Upper Cretaceous of Uzbekistan, has been assigned variously as a member of Ceratopsidae (the clade including Triceratops and relatives; Nessov et al. 1989), sister taxon to Ceratopsidae (e.g., Sereno 1997), or a nomen dubium (e.g., Dodson et al. 2004). Cladistic affiliation is of considerable importance for this problematic taxon because all other members of the diverse Ceratopsidae are restricted to western North America. In a recent paper published in Naturwissenschaften, (Sues and Averianov 2009) described newly recovered specimens of Turanoceratops and conducted a cladistic analysis of Ceratopsia. Based on their study, the authors concluded that Turanoceratops is indeed a member of the less inclusive Ceratopsidae and, thus, represents “the first definite ceratopsid dinosaur recorded from Asia.” This result has important implications for the biogeography, origin, and evolution of horned dinosaurs. The ingroup taxa used for their phylogenetic analysis of Turanoceratops (Sues and Averianov 2009) included a thorough representation of non-ceratopsid ceratopsians, but ceratopsids were restricted to two genera (Centrosaurus and Triceratops). Additionally, the source matrix (Makovicky and Norell 2006) was not focused on Ceratopsidae, so many informative phylogenetic characters pertaining to the clade were not included. In order to better evaluate the phylogenetic relationships of Turanoceratops relative to Ceratopsidae, we scored the taxon for the matrix previously published by Dodson et al. (2004). This matrix includes Protoceratops as an outgroup, Zuniceratops, and 13 ceratopsid genera. Eight out of 73 characters were scored for Turanoceratops as follows (character number followed by state in parentheses): 21(1), 22(0), 25(0), 29(0), 57(0), 60(1), 61(1), and 62(0). The matrix was analyzed in PAUP* (Swofford 2003), and three equally parsimonious trees (length=85, consistency index=0.9059, retention index=0.9437) were recovered (Fig. 1). In all three trees, Turanoceratops fell outside of Ceratopsidae (defined as all taxa descended from the most recent common ancestor of Triceratops and Centrosaurus; Dodson et al. 2004), and an additional two steps were required to move Turanoceratops within Ceratopsidae. Turanoceratops lacks at least two features shared by all ceratopsids in this data set: a true supracranial sinus complex and reduced subsidiary ridges on the teeth. The postorbital is remarkably similar to that of the derived neoceratopsian Zuniceratops, particularly in the presence of Naturwissenschaften (2009) 96:869–870 DOI 10.1007/s00114-009-0543-8