Lanasaurus scalpridens, GOW, 1975

Norman, David B., Crompton, Alfred W., Butler, Richard J., Porro, Laura B. & Charig, Alan J., 2011, The Lower Jurassic ornithischian dinosaur Heterodontosaurus tucki Crompton & Charig, 1962: cranial anatomy, functional morphology, taxonomy, and relationships, Zoological Journal of the Linnean Society 163, pp. 182-276 : 239-240

LANASAURUS SCALPRIDENS GOW, 1975

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 )].

Holotype horizon 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. scalpridens on the basis of the holotype maxilla, 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. scalpridens might be represent the same taxon as A. consors . Thulborn (1978) considered La. scalpridens to be highly atypical for heterodontosaurids, and even questioned its heterodontosaurid affinities. Hopson (1980:94) first suggested that Lanasaurus might be synonymous with Ly. angustidens and 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 Lanasaurus to Lycorhinus is not compelling and cannot be proven using any currently available specimens. One obvious problem with any comparison between Lanasaurus and Lycorhinus is 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. scalpridens as a distinct and diagnosable taxon. Two potential autapomorphies of La. scalpridens are 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 holotype of 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 Lanasaurus from Heterodontosaurus and Abrictosaurus have 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. angustidens is also referred to La. scalpridens . As discussed above for the holotype of La. scalpridens, BP /1/5253 cannot be referred to Ly. angustidens with any confidence because it does not overlap anatomically with the holotype specimen of the latter taxon. However, BP/1/5253 does show close resemblances to BP/1/4244, the holotype of 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 Heterodontosaurus and 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 Lanasaurus appears 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 Lanasaurus and 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 Lanasaurus and Lycorhinus are distinct taxa, because the dentary of NHMUK RU A100 differs in several respects from that of Ly. angustidens (discussion above).

Figures

Figure 38. NHMUK RU A100 (BMNH A100). Unnamed heterodontosaur remains based on a partial skull that was originally referred to the genus Lycorhinus by Thulborn (1970b) – composite image manipulated to create the effect of a partial anterior skull viewed from left side. A, left premaxilla in medial view (reversed). B, left maxilla in lateral view. C, maxillary dentition in medial view (reversed). D, left dentary in medial view (reversed). Illustrations derived from Charig & Crompton (1974: figs 4–7).

Figure 39. A, Abrictosaurus consors (Thulborn, 1974). NHMUK RU B54 (holotype). A partial skull (illustrated in abstract form – and based on the reconstruction in Thulborn, 1978). Shading represents known elements of the skull and dentition. The specimen includes postcranial elements that (along with the skull) are in need of further preparation and re-description. B, Abrictosaurus consors (Thulborn, 1974). NHMUK RU B54 (holotype). The maxillary and dentary dentitions, as drawn by Thulborn (1974: fig. 3). C, Lanasaurus scalpridens Gow, 1975. BP/1/4244 (holotype). The maxillary dentition in medial aspect [reversed for comparison with (B)] showing the almost complete dentition (crown 12 obliquely truncated) and with the individually angled wear facets accentuated by cross-hatching (redrawn from Hopson, 1980: fig. 2).