Ratchasimasaurus suranareae Basal neornithischian indet. ('Khok Sanam neornithischian' )

Manitkoon, Sita, Deesri, Uthumporn, Warapeang, Prapasiri, Nonsrirach, Thanit & Chanthasit, Phornphen, 2023, Ornithischian dinosaurs in Southeast Asia: a review with palaeobiogeographic implications, Fossil Record 26 (1), pp. 1-25 : 1

Ratchasimasaurus suranareae Basal neornithischian indet. ('Khok Sanam neornithischian')

Material.

WNM-Ks-001, an isolated tooth (Fig. 4C-E ).

Locality and age.

Khok Sanam locality, Kham Muang District, Kalasin Province; the lower Phu Kradung Formation, Late Jurassic.

Comments.

A dentary tooth shows the fan-shaped crown, and has the characters of the posterior teeth present in the dentary teeth of PRC 149 ( Buffetaut et al. 2014) and of Nanosaurus agilis ( Carpenter and Galton 2018). Although the enamelled surface is thin, a well-developed ornamentation of ridges is still noticeable on the lingual side as the enamel is asymmetrically distributed. The margin of the laterally compressed crowns bears distinct denticles. The labial side of the tooth bears no enamel and shows worn facets. The ornamented lingual side does not show a prominent median ridge, contrasting with the European Early Cretaceous Hypsilophodon foxii ( Galton 2009) and other derived neornithischians. There is moderately developed labiolingual expansion ( ‘cingulum’) at the base of the crown, as seen in basal neornithischians ( Barrett et al. 2005). The cylindrical root has been preserved and curves to the labial side.

Figures

Figure 4. Basal neornithischian specimens from the lower Phu Kradung Formation. (left) Left dentary (PRC 149) from Phu Noi locality, in lateral (A) and medial (B) views; (right) isolated tooth (WNM-Ks- 001) from Khok Sanam locality, in labial (if dentary) (C), lingual (D) and mesial / distal (E) views. Scale bars: 5 cm (A, B); 1 cm (C-E).