Eromangasaurus australis (Sachs, 2005), 2021

Vakil, Vikram, Webb, Gregory & Cook, Alex, 2021, Taxonomic utility of Early Cretaceous Australian plesiosaurian vertebrae, Palaeontologia Electronica (a 30) 24 (3), pp. 1-44 : 8

Eromangasaurus australis (Sachs, 2005)

Figure 4

1982 Woolungasaurus cf. W. glendowerensis Persson , p. 648, Pl. 1, figs.1, 2, Pl. 2, fig. 1.

1993 Elasmosauridae , gen. et sp. nov. Thulborn and Turner, figs. 2, 3.

2003 Elasmosauridae , gen. et sp. nov. Kear, fig. 3A.

2004 Tuarangisaurus , sp. nov. Sachs, p. 713.

2005 Tuarangisaurus australis Sachs , p. 426, figs. 2-5.

2005b Eromangasaurus carinognathus Kear , p.

793, figs. 2-7.

2007 Eromangasaurus australis (Sachs, 2005) comb. nov., Kear, p. 244, figs. 1, 2.

Holotype. QM F11050 . Nearly complete, but badly crushed skull (including atlas-axis complex) plus five cervical vertebrae, including three isolated anterior cervical vertebrae ( QM F12216 and QM

F12219a,b) and two more posterior cervical vertebrae ( QM F12217). An additional ventral impres-

sion of QM F12216 containing minor bone fragments is labelled QM F12218 (see Appendix

Table 2 for vertebrae specimen numbers).

Locality. Yambore Creek, north of Julia Creek,

central northern Queensland.

Stratigraphic horizon. Toolebuc Formation (early

Aptian – late Albian).

Diagnosis. See Kear (2007).

Description. The skull and atlas-axis complex of this individual have been described previously

(Sachs, 2005; Kear, 2005b, 2007) and are not dealt with here. Specimens QM F12216 and QM

F12217 also have been described previously

(Persson, 1982; Sachs 2005), and the description below is taken from them with additional observations and measurements. Sachs (2005) labelled one vertebra as QM F12216-19, but illustrated only QM F12216 (his figure 5B), apparently not having had access to the last two vertebrae recovered (which make up QM F12219). Vertebrae include three anterior cervical vertebrae free of matrix (QM F12216, QM F12219a,b; mean CW = 69.5 mm; mean CL = 67.4 mm; mean CH = 50.9 mm) and two mid- to posterior cervicals that are cojoined but free of matrix (QM F11217; CW = 104.15, 105.2 mm; CL = 99.05, 98.15 mm; CH = 84.45, 87.65 mm) (all measurements in Appendix Table 1). All centra are complete, with distinct foramina subcentralia. Anterior cervical vertebrae (QM F12216 and QM F12219) ( Figure 4A , D-G) have dumbbell-shaped articular facets, a lateral ridge, latero-ventrally placed rib facets borne wholly on the centrum, part of the neural arch facet on the dorsal surface and narrowly-spaced foramina subcentralia. The cojoined vertebrae (QM F12217) ( Figure 4B, C ) have neural arches and parts of neural spines fused to centra with a faint suture, dumbbell-shaped articular facets, a prominent ridge on the lateral surface but positioned towards the rib facets, laterally positioned but widely-spaced rib facets, and relatively widely-spaced foramina subcentralia.

Remarks. The original sequence of vertebrae is lost and the current sequence is based on morphology and size with the anterior specimens most similar in size to the atlas-axis complex and the cojoined pair (QM F12217) being significantly larger ( Figure 4 ). This specimen has a complex collection history, detailed by Persson (1982), with even the skull being collected in two parts at separate times. This has created some confusion in numbering, with the last two collected centra becoming separated from the skull and first collected centra within the QM collection (Appendix Table 2). As a result, one of the QM F12219 centra was erroneously labelled QM F12217, duplicating the number of the original cojoined specimens. However, Persson (1982) made it clear that QM F12219 represented two separate centra. Adding to the complexity is that whereas the three smaller anterior centra share similar matrix with the skull and atlas-axis complex, the cojoined specimens (QM F12217) have somewhat different matrix. Regardless, all vertebrae appear to be associated with the skull based on field notes despite the great disparity in size of QM F12217. Based on the osteological immaturity of the vertebrae and atlas-axis complex, Persson (1982) considered the specimen a subadult.

Figures

FIGURE 4. Vertebrae associated with specimen QM F11050 – Eromangasaurus australis holotype. A. QM F12216, lateral view showing lateral ridge (red arrow). B. Cojoined vertebrae QM F12217, anterior view. C. QM F12217, lateral view showing lateral ridges (red arrows). D. QM F12219a, anterior view. E. QM F12219a, lateral view showing lateral ridge (red arrow). F. QM F12219b, lateral view showing lateral ridge (long red arrow) and rib facet borne wholly on centrum (short red arrow). G. QM F12219b, ventral view showing foramina subcentralia (white arrows) separated by a mid-ventral keel. Scales shown on figure.