TAXONOMIC CLARIFICATION OF THE AUSTRALIAN ELASMOSAURID GENUS EROMANGASAURUS, WITH REFERENCE TO OTHER AUSTRAL ELASMOSAUR TAXA

Australian plesiosaur paleontology has undergone a renaissance in recent years with a number of studies examining aspects of taxonomy and phylogenetic relationships (e.g., Cruickshank et al., 1999; Kear, 2001, 2002, 2003, 2004, 2005a, 2005b; Sachs 2004, 2005a). No plesiosaur group has received greater attention than the ubiquitous Elasmosauridae, a clade of long-necked plesiosauroid plesiosaurs best known (in Australia) from the late Early Cretaceous (Aptian-Albian) epicontinental marine deposits of the central and northeastern part of the continent. The earliest recorded Australian elasmosaurs were described by McCoy (1867), who erected two species, ‘Plesiosaurus’ sutherlandi McCoy, 1867 and ‘Plesiosaurus’ macrospondylus McCoy, 1867, based on isolated vertebrae from the Flinders River region of northern Queensland. Later studies (Persson, 1960, Welles, 1962) recognized these taxa as nomina dubia and independently referred them both to Elasmosauridae indet (see Kear, 2003 for a summary of taxonomic history). Probably the best known Australian elasmosaurid, ‘Woolungasaurus glendowerensis’ Persson, 1960, was established on the basis of a fragmentary postcranial skeleton (QM F3567) from the Aptian Wallumbilla Formation of northwestern Queensland. Unfortunately, this taxon has since become a wastebasket, containing many non-diagnostic Australian elasmosaur remains (e.g. Persson, 1960; Ludbrook, 1960; Freytag, 1964). Welles (1962) and Kear (2003) considered ‘Woolungasaurus’ (sic ‘W. glendowerensis’) to be a nomen dubium. Sachs (2004), however, resurrected the taxon but changed its generic-level assignment to Styxosaurus Welles, 1943, a genus known elsewhere from the Late Cretaceous (Campanian) Niobrara Formation of western North America. This placement was based solely on broad similarities in the postcranium, none of which constituted unequivocal synapomorphies specifically uniting ‘W. glendowerensis’ and Styxosaurus to the exclusion of all other elasmosaurids (see Kear, 2005a for character list). In addition, no unambiguous apomorphic characters nor cladistic anlysis was provided to adequately justify ‘Styxosaurus glendowerensis’ as a distinct species. As a result, Kear (2005a) reassigned both the type and referred specimens to Elasmosauridae indet. (sensu Kear, 2003) pending discovery of more diagnostic, preferably cranial, material. The only potentially valid Australian elasmosaurid (here designated ‘QM F11050’) has been described on the basis of an articulated although badly crushed skull (QM F11050), from the Upper Albian Toolebuc Formation of central northern Queensland. Persson (1982) provided a brief description of this specimen, tentatively attributing it to ‘Woolungasaurus cf. glendowerensis. ’ Thulborn and Turner (1993), however, found no sound taxonomic basis for this assignment, and thus referred QM F11050 (pending a more thorough description and reappraisal) to a possible new unnamed genus and species of elasmosaurid closely resembling Libonectes Carpenter, 1997 from the Turonian (Upper Cretaceous) Britton Formation of Texas, U.S.A. (see Carpenter, 1997). Kear (2003) followed this temporary placement, although Sachs (2004) suggested an alternative assignment to Tuarangisaurus Wiffen and Moisley, 1986, a taxon known elsewhere from the Maastrichtian Maungataniwha Member (Tahora Formation) of New Zealand, and potentially the upper Maastrichtian Jagüel Formation of Patagonia (see Wiffen and Moisley, 1986; Gasparini et al., 2003). Subsequent reexamination by Kear (2005a) however, showed that the holotype skull of Tuarangisaurus (NZGS CD425) differed markedly from that of QM F11050 (see Kear, 2005a for character list and cladistic analysis); moreover, the presence of several discrete autapomorphies (together with unique combination of characters variously developed in other elasmosaurs) prompted the establishment of a new genus and species Eromangasaurus carinognathus Kear, 2005a. As this work appeared in print, Sachs (2005a) published a second separate study, which again proposed assignment to Tuarangisaurus but erected a new species designation ‘T. ’ australis Sachs, 2005a. Notably, Sachs’s (2005a) description of the holotype (QM F11050) differed from that of Kear (2005a) in its interpretation of several anatomical features. In addition, the cladistic anlaysis provided by Sachs (2005a) scored both QM F11050 and Tuarangisaurus as a single taxon and thus did not test the independent placement of QM F11050 relative to other elasmosaurids. This article aims to evaluate these discrepancies via a detailed re-examination of the original holotype skull (QM F11050); a revised taxonomic assignment is also proposed for the specimen. Institutional Abbreviations—NZGS, New Zealand Geological Survey, Lower Hutt, New Zealand; QM, Queensland Museum, Brisbane, Australia.