Wintonotitan wattsi, Hocknull, White, Tischler, Cook, Calleja, Sloan & Elliott, 2009

D, Michael D. & Emic, 2012, The early evolution of titanosauriform sauropod dinosaurs, Zoological Journal of the Linnean Society 166 (3), pp. 624-671 : 650-651

WINTONOTITAN WATTSI (HOCKNULL ET AL., 2009)

Longman (1933) named Austrosaurus mckillopi on the basis of several fragmentary dorsal vertebrae (QMF 2316) from the Early Cretaceous Allaru Mudstone of Australia. Hocknull et al. (2009) regarded Austrosaurus as a nomen dubium and named a new genus – Wintonotitan – from the slightly younger Winton Formation based on materials that had previously been referred to Austrosaurus sp. (QMF 7292). Wintonotitan was diagnosed by a combination of many characters (see Hocknull et al., 2009: 16). Two features were cited as autapomorphies: dorsal vertebrae with ‘incipient’ spinoprezygapophyseal lamina, and cylindrical, incipiently biconvex distal caudal vertebrae. Both of these features characterize a wider array of basal titanosauriforms, however. An ‘incipient’ (subtle or small) spinoprezygapophyseal lamina (i.e. anterior spinodiapophyseal lamina) is found in several titanosauriforms (e.g. Ligabuesaurus , Sauroposeidon , Giraffatitan , Argentinosaurus , pers. observ.). Likewise, weakly biconvex, cylindrical distal caudal vertebrae are found in Giraffatitan and Rinconsaurus (pers. observ.). These features may be local autapomorphies, but this awaits determination via cladistic analysis. However, the validity of Wintonotitan is supported by one unique feature recognized herein, distal caudal vertebrae with strongly arched ventral surfaces (see Hocknull et al., 2009: fig. 14).

Hocknull et al. (2009) recovered Wintonotitan as a member of Laurasiformes or the sister taxon of Malarguesaurus in modified versions of the matrices of Canudo et al. (2008) and González Riga et al. (2009), respectively, but did not rule out titanosaur affinities for the genus. These results were supported by low bootstrap values ( Hocknull et al., 2009: fig. 38) and the node supporting Wintonotitan and other titanosauriforms had a decay index of 2 in each analysis. The results of the present analysis suggest that Wintonotitan is a titanosauriform on the basis of reduced metacarpal phalangeal articular facets (Appendix 3), but more precise knowledge of its affinities await future discoveries and studies.