Xinpusaurus kohi

LIU, JUN & RIEPPEL, OLIVIER, 2005, Restudy of Anshunsaurus huangguoshuensis (Reptilia: Thalattosauria) from the Middle Triassic of Guizhou, China, American Museum Novitates 3488, pp. 1-35 : 27-30

‘‘ X. kohi ’’ (GMPKU2000/005). So the coding for both species of Xinpusaurus is ‘‘0’’.

14. Posterolateral processes of frontal do not extend beyond anterior margin of lower temporal fossa (0), extend far beyond anterior margin of lower temporal fossa (1), are absent (2). [R10, L10, J9, M14]

The posterolateral processes are moderately developed in Petrolacosaurus and Prolacerta , well developed in Youngina . So the polarity is changed.

15. Frontoparietal suture interdigitating, oriented transversely for most of its part (0) or deeply embayed in the shape of a broad V, the apex pointing forward (1). [L17, J16, M16]

16. Postfrontal and postorbital separate (0) or fused (1). [N16, R12, L12, J11, M17]

17. Posterior end of squamosal with (0) or without ventral process (1). [R14, L14, J14, M19]

18. Quadrate without (0) or with (1) distinct medial lamina. [M20]

19. Pineal foramen large and located in front of midpoint of parietal skull table (0) or small and located at center or somewhat behind parietal skull table (1). [R16, L16, J15, M22] The polarity is changed.

LOWER JAW

20. Dorsal margin of dentary symphysis straight (0), recurved (1). [N22]

21. Surangular and angular equally well exposed on the lateral side of lower jaw (0) or surangular exposure much more extensive (1). [J24] Coding for Askeptosaurus as ‘‘1’’.

TEETH

22. Premaxilla dentition is present (0) or absent (1) (state 1 includes also pseudodont projections). [N29, M3]

23. Diastema between premaxillary and maxillary teeth absent (0), present (1). [N28, R3, L3, J3, M4]

24. Anteriormost dentary teeth upright (0), procumbent as their implantation curves around anterior end of dentary (1). [R4, L4, M5]

25. Posterior teeth on dentary conical and pointed (0), bulbous and blunt (1). [part of R5, L5, J4, M6]

The character definition is revised, so the coding has changed for Xinpusaurus (1).

26. Palatal dentition (on vomer and pterygoid) present (0) or absent (1). [N25, 26, 27 M7, 8, 9]

POSTCRANIAL

27. Number of cervical vertebrae is less than 10 (0) or higher than 10 (1). [N35, M24]

28. Neural spines of posterior cervicals and dorsals are relatively low (0) or at least two times higher than broad (1). [M28, J27]

29. Proximal caudal neural spines are relatively low (0) or distinctly elongated and at least three times higher than broad (1). [M29]

Because the postcranium of Xinpusaurus ‘‘ kohi ’’ appears to be a composite and it is not known in the holotype of X. bamaolinensis , coding is ‘‘?’’ in this species.

30. Scapula is slender and elongate (0) or broad and rounded (1).

31. Deltopectoral crest is well developed (0) or reduced (1). [N38, M26]

32. Radius is slender (0), slightly expand­ ed (1), or strongly expanded and roughly kidney shaped (2). [J28]

33. Femur proximal and distal ends about equal in width (0) or distal end markedly widened (1). [J29]

34. Fibula distal end narrow, that is, width less than half of length (0), expanded (1).

Some characters included in former studies are deleted from this analysis because they are uninformative for the analysis of ingroup relationships. These characters include:

1. Nasals meet each other medially (0) or are separated due to the posterior extent of the premaxilla (1). [M10]

2. Anteromedial processes of frontals that enter in between nasal and premaxilla are shorter (0) or longer (1) than anterolateral processes of frontal. [R9, L9, J8]

3. The quadratojugal is present (0) or absent (1). [M21]

4. Lacrimal present (0) or absent (1). [N12, J18]

5. Upper temporal fenestra present and large (0), reduced and slitlike (1), or absent (2). [N1, R13, L13, J12, M18]

All multistate characters were treated unordered and unweighted. Implementing branch­and­bound search option of the PAUP* 4.0b10 ( Swofford, 2001), the 15 most parsimonious trees resulted, with a length of 62 (consistency index 0.65, retention index 0.77). In the strict consensus tree (fig. 13), the monophyly of Askeptosauridae (see Rieppel et al., 2000) and Thalattosauroidea ( Nopsca, 1928; see also Rieppel 1987) are recovered, Endennasaurus is the sister taxon of Askeptosauridae , Thalattosaurus and Xinpusaurus are monophyletic genera, Paralonectes and Nectosaurus from North America are closely related to Clarazia and Hescheleria from Monte San Giorgio.

Askeptosaurus and Anshunsaurus are unequivocally diagnosed by the rostrum tapering to a blunt tip (Char. 2[2], CI 5 1), the maxilla is shorter than the part of the premaxilla forming the upper jaw maxilla (Char. 6[1], CI 5 0.50), and the frontoparietal suture interdigitating, oriented transversely for most of its part (Char. 15[0], CI 5 0.33). Based on DELTRAN character optimization, the shared characters also include the nasal extends backward to a level behind the anterior margin of the orbit (Char. 9[1], CI 5 1).

The family Askeptosauridae (Kuhn­ Schnyder, 1952) included only one genus and species for a long time. Anshunsaurus was included as the second member of this group ( Rieppel et al., 2000), although the monophyly of this family is in doubt. Endennasaurus was proposed as being closely related to thalattosaurs, especially Askeptosaurus , by the nominator ( Renesto, 1992). This opinion was accepted by Nicholls (1999), but not accepted and excluded in our previous analysis ( Rieppel et al., 2000). Subsequent research by Müller et al. (2005) supported its position as a thalattosaur. In this study, it also turns out to be closely related to Askeptosaurus and Anshunsaurus . So it is reasonable to include Endennasaurus in Askeptosauroidea ( Kuhn­Schnyder, 1971). The unequivocal synapomorphies include: premaxilla has no distinct posteroventral process extending beyond the anterior narial margin in ventral side (Char. 5[1], CI 5 1); posterolateral processes of frontal extending far beyond anterior margin of lower temporal fossa (Char. 14[1], CI 5 0.67); palatal dentition (on vomer and pterygoid) absent (Char. 26[1], CI 5 1); the number of cervical vertebrae more than 10 (Char. 27[1], CI 5 1); and the scapula broad and rounded (Char. 30[1], CI 5 0.5).

The monophyly of Thalattosauroidea is supported by all analyses including this one ( Nicholls, 1999; Rieppel et al., 2000; Liu and Rieppel, 2001; Müller, 2002; Jiang et al., 2004). An unequivocally shared derived character of this group is dorsal margin of dentary symphysis recurved (Char. 20[1], CI 5 1). Based on ACCTRAN character optimization, the shared characters also include tip of snout (rostrum) slightly deflected ventrally (Char. 3[1], CI 5 0.5), anterolateral processes of frontal closely approach external naris (Char. 10[1], CI 5 1), nasal separated from prefrontal (Char. 11[1], CI 5 1), prefrontal with shieldlike extension along the anterodorsal orbital margin (Char. 12[1], CI 5 0.5), pineal foramen small and located at center or somewhat behind parietal skull table (Char. 19[1], CI 5 0.5), neural spines of posterior cervicals and dorsals at least two times higher than broad (Char. 28[1], CI 5 0.5), proximal caudal neural spines distinctly elongated and at least three times higher than broad (Char. 29[1], CI 5 1), the radius strongly expanded and roughly kidney shaped (Char. 32[2], CI 5 1), the femur distal end markedly widened (Char. 33[1], CI 5 1), the slender fibula (Char. 34[1], CI 5 0.5).

The intrarelationships of Thalattoauroidea are different from all previous results, although the exact relationships of the four genera are still unclear. Although Claraziidae ( Peyer, 1936b) may be monophyletic, Thalattosauridae ( Merriam 1904) is definitely not. A sister relationship of Xinpusaurus with Nectosaurus is not supported by this study.