Ratchasimasaurus suranareae Basal neornithischian indet. ('Phu Noi 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. ('Phu Noi neornithischian')

References.

Buffetaut et al. 2014; Manitkoon et al. 2019.

Material.

PRC 149 (renumbered from PN 13-09 in Buffetaut et al. (2014)), a lower jaw (Figs 3B , 4A, B ); PRC 150, an articulated postcranial skeleton ( Manitkoon et al. 2019) (Fig. 3C ).

Locality and age.

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

Previous study.

Buffetaut and his team reported a lower jaw (PRC 149) from the Phu Noi locality. The fan-shaped teeth with a strongly ridged crown and an asymmetric enamel distribution suggests that the specimen belongs to a small ornithopod dinosaur ( Buffetaut et al. 2014). A well-preserved articulated small ornithischian skeleton without skull (PRC 150) was reported from the same locality ( Manitkoon et al. 2019). The pre-acetabular process of the ilium is narrow, long with a perfectly rounded termination and slightly ventrally curved. The post-acetabular process is short and high. A combination of characters resembles those Jurassic basal neornithischians from China, such as Agilisaurus louderbacki and Hexinlusaurus multidens ( Manitkoon et al. 2019).

Comments.

Many taxa of basal neornithischians, once considered as early members of ornithopods, have been reclassified as the basal neornithischians ( Boyd 2015; Madzia et al. 2018, 2021; Dieudonné et al. 2020). The similarities to the Chinese taxa, for example, the axial skeleton, is composed of 15 dorsal and five sacrals; the Brevis shelf of the ilium is visible in lateral view along the entire length; a distinct supra-acetabular flange on the pubic peduncle of the ilium; prepubis tip extends beyond the distal end of the pre-acetabular process of ilium, suggesting PRC 149 is a basal neornithischian outside the clade Ornithopoda . Numerous limb bones of various sizes from basal neornithischians were also found at the Phu Noi site, indicating that these dinosaurs were abundant in this area. It is the oldest neornithischian known, so far, from southeast Asia. Agilisaurus louderbacki and Hexinlusaurus multidens exhibit symmetrically distributed enamel ( Peng 1992; Barrett et al. 2005), but the dentary teeth of PRC 149 and other isolated teeth from Phu Noi are different in having asymmetrically distributed enamel on the teeth as in Yandusaurus hongheensis from the upper Shaximiao Formation, Nanosaurus agilis (= Drinker , Othnielia , Othnielosaurus ) from the Late Jurassic Morrison Formation, and a variety of more derived neornithischians ( Barrett et al. 2005; Butler et al. 2008; Galton 2009; Carpenter and Galton 2018). Preliminary comparisons seem to indicate that it is a new taxon ( Buffetaut et al. 2014; Manitkoon et al. 2019).

Figures

Figure 3. Exceptional specimen of ornithischian dinosaurs from Thailand. Stegosaurid vertebra (A. SM 2011 - 1 - 001), Phu Noi neornithischian left dentary (B. PRC 149), Phu Noi neornithischian articulated skeleton (C. PRC 150), Dan Luang neornithischian left femur (D. SM 2016 - 1 - 081), Psitacosaurus indet. Right femur (E. SM 2016 - 1 - 080), Psitacosaurus sattayaraki right dentary (F. SM 2016 - 1 - 163), Khok Pha Suam iguanodontian dorsal vertebra (G. SM 2021 - 1 - 113), Khok Pha Suam iguanodontian left femur (H. SM 2021 - 1 - 118), Siamodon nimngami left maxilla (I. PRC- 4), Ratchasimasaurus suranareae left dentary (J. NRRU-A 2064), Sirindhorna khoratensis left maxilla (K. NRRU-A 2048), Sirindhorna khoratensis right dentary (L. NRRU 3001 - 167); A and G in anterior view; B-D, and H-J in lateral view; E, F and L in medial view. Scale bars: 10 cm (A, C-E, G-L); 5 cm (B, F).

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).