The Lower Jurassic ornithischian dinosaur Heterodontosaurus tucki Crompton & Charig, 1962: cranial anatomy, functional morphology, taxonomy, and relationships Norman, David B. Crompton, Alfred W. Butler, Richard J. Porro, Laura B. Charig, Alan J. Zoological Journal of the Linnean Society 2011 163 182 276 GOW, 1975 Gow 1975 [227,675,198,220] Reptilia Heterodontosauridae Lanasaurus GBIF Animalia Ornithischia 57 237 Chordata species scalpridens   Revised diagnosis:Maxillary tooth row that is strongly bowed inwards along its length; maxillary teeth in labial view possess a posterior ridge that is significantly more strongly developed than is the anterior ridge.   Holotype:BP/1/4244, left maxilla [ Fig. 39C; Gow, 1975: figs 1, 2, pl. 1, Hopson, 1980: fig. 2, Galton, 1986: fig. 16.6o–p, Gow, 1990: fig. 6, Weishampel & Witmer, 1990: fig. 23.2a (as  Ly. angustidens), Norman et al., 2004c: fig. 18.2a (as  Ly. angustidens)].    Holotypehorizon and locality: Upper Elliot Formation, ‘ Buck Camp’, Golden Gate Highlands National Park( 28°30′S, 28°37′E; Kitching & Raath, 1984: table 1), Free State Province, South Africa.  Referred specimens:BP/1/5253, partial left maxilla, unspecified stratigraphical level, Bamboeskloof Farm ( 30°45′S, 27°12′E; Gow, 1990), Lady Grey, Eastern Cape Province, South Africa( Gow, 1990: figs 1, 3–5). NHMUK RU A100 (formerly UCL A100), partial skull, upper Elliot Formation at Paballong ( 30°26′S, 28°31′E; Kitching & Raath, 1984: table 1), near Mount Fletcher, Herschel district, Eastern Cape Province, South Africa[ Thulborn, 1970b: figs 1–5; Charig & Crompton, 1974: figs 4–7; Hopson, 1975: fig. 3a–b; Galton, 1986: fig 16.6n(as  Abrictosaurus consors); Weishampel & Witmer, 1990: fig 23.2b (as  A. consors); Smith, 1997: fig 3a, b (as  A. consors); Norman et al., 2004c: fig 18.2b (as  A. consors)].  Discussion: Gow (1975)named  La. scalpridenson the basis of the holotypemaxilla, diagnosing it on the basis of its dental morphology, the presence of a maxillary tooth row that bows medially (toward the midline) along its length, and the absence of the accessory openings within the antorbital fossa identified in  Heterodontosaurus. Gow (1975)did, however, speculate that  La. scalpridensmight be represent the same taxon as  A. consors. Thulborn (1978)considered  La. scalpridensto be highly atypical for heterodontosaurids, and even questioned its heterodontosaurid affinities. Hopson (1980:94)first suggested that  Lanasaurusmight be synonymous with  Ly. angustidensand was supported by Gow (1990), Weishampel & Witmer (1990), Norman et al. (2004c), and Butler et al. (2008b).  Gow (1990)did not evaluate the characters that supported his tentative reference to  Abrictosaurus; it is however evident that they included general similarities in dental wear patterns. The assignment of  Lanasaurusto  Lycorhinusis not compelling and cannot be proven using any currently available specimens. One obvious problem with any comparison between  Lanasaurusand  Lycorhinusis their nonoverlapping holotypes, respectively: BP/1/4244 is a maxilla and SAM-PK-3606 is a dentary. It is considered preferable to provisionally retain  La. scalpridensas a distinct and diagnosable taxon. Two potential autapomorphies of  La. scalpridensare here recognized:     1. The presence of a maxillary tooth row that is strongly bowed inwards along its length ( Gow, 1975); and   2. Maxillary teeth in lateral view possess a posterior ridge that is significantly more strongly developed than the anterior ridge. Although Gow (1990)reported an inwardly arched tooth row in the holotypeof  Ly. angustidens(SAM- PK-3606) it has not been possible to confirm this [based upon examination of a latex cast of SAM-PK- 3606 (NHMUK R8180)]. Characters that distinguish  Lanasaurusfrom  Heterodontosaurusand  Abrictosaurushave been discussed above.   BP/1/5253 A second specimen, the partial left maxilla (BP/1/ 5253) described by Gow (1990)and assigned by him to  Ly. angustidensis also referred to  La. scalpridens. As discussed above for the holotypeof  La. scalpridens, BP/1/5253 cannot be referred to  Ly. angustidenswith any confidence because it does not overlap anatomically with the holotypespecimen of the latter taxon. However, BP/1/5253 does show close resemblances to BP/1/4244, the holotypeof  Lanasaurus, as discussed by Gow (1990). Both maxillae share the possible autapomorphies of having a tooth row that is strongly bowed inwards along its length and teeth with posterior ridges on their lateral surfaces that are more pronounced than the anterior ridges. These maxillae share other similarities, such as the anterodorsal margin of the antorbital fossa not being sharply defined, as occurs in  Heterodontosaurusand  Abrictosaurus. Few meaningful differences occur between BP/1/5253 and BP/1/4244: the tooth row of the former is marginally more strongly curved inwards along its length and foramina cannot be recognized within the buccal emargination; both of these differences may reflect post-mortem effects rather than genuine anatomy. In light of the presence of shared potential autapomorphies, and only minor differences, referral of BP/1/5253 to  Lanasaurusappears justified.  NHMUK RU A100 This controversial specimen is referred, provisionally, to  La. scalpridens. The specimen has been referred to both  Ly. angustidens( Thulborn, 1970b, 1974, 1978; Gow, 1990) and  A. consors( Hopson, 1975; Weishampel & Witmer, 1990); however, neither can be supported (discussion above). Several right maxillary teeth of NHMUK RU A100 are well exposed in lateral view ( Fig. 38– and Thulborn, 1970b: fig. 3). These have a similar general morphology and degree of packing to  Lanasaurusand they share, with  Lanasaurus, the presence of posterior ridges on the lateral surfaces of the crowns that are more pronounced than the anterior ridges. As preserved, the right tooth row of NHMUK RU A100 is bowed inwards along its length, and curves outwards markedly at its anterior end. The curvature of the tooth row, particularly at the caudal end, is not as pronounced as in BP/1/4244, but this may be a post-mortem artefact. In view of the fact that NHMUK RU A100 possesses one autapomorphy of  La. scalpridens, it is referred tentatively to this latter taxon. If this proves correct (by further preparation and study of NHMUK RU A100) it may demonstrate that  Lanasaurusand  Lycorhinusare distinct taxa, because the dentary of NHMUK RU A100 differs in several respects from that of  Ly. angustidens(discussion above). South Africa Golden Gate Highlands National Park -28.5 Upper Elliot Formation 1232 28.616667 Buck Camp' 57 239 1 Free State holotype