Reassessment of the non‐titanosaurian somphospondylanWintonotitan wattsi(Dinosauria:Sauropoda:Titanosauriformes) from the mid‐CretaceousWintonFormation,Queensland,Australia

Abstract

Wintonotitan wattsi, a Cretaceous titanosauriform sauropod from central Queensland, Australia, is redescribed following a full revision of its osteology. The holotype specimen, a partial postcranial skeleton derived from the lower Upper Cretaceous Winton Formation, comprises axial and appendicular elements. Wintonotitan has been commonly resolved as a non‐titanosaurian somphospondylan titanosauriform since its description, in contrast to its more derived contemporary Diamantinasaurus matildae. We provide a detailed redescription, taking this opportunity to correct four misinterpretations made in the original description of Wintonotitan that impact on our understanding of this taxon: the right ulna was originally described as the left and vice versa; the left metacarpus was incorrectly described as being from the right side; metacarpal IV was described as metacarpal V and vice versa; and the ilium was incorrectly oriented. The reassessment of the metacarpus is particularly important, since it shows that a proximal fossa is present on metacarpals I, II and III, which might have been occupied by either the strongly convex distal end of the radius or a (possibly unossified) carpal element. We provide a review of titanosauriform metacarpal morphology to support our reassessments. Our revision of the osteology of Wintonotitan results in the identification of several previously unrecognized autapomorphies, augmenting and revising its original diagnosis. We provide additional support for the previous referral of four caudal vertebrae from south‐east of Winton, Queensland, to W. wattsi. Furthermore, we demonstrate that a tentative report of titanosaur osteoderms from the Winton Formation was based on misidentification of dorsal vertebral neural spines pertaining to the holotype of W. wattsi. Consequently, titanosaur osteoderms are currently unknown from Australia. Following our revision and reinterpretation of a number of elements, we re‐examine the phylogenetic placement of Wintonotitan, supporting its position as a non‐titanosaurian somphospondylan titanosauriform, with no close relationship with the contemporaneous lithostrotian titanosaur Diamantinasaurus.

Depositional Environment of the Lower Cretaceous (Upper Albian) Winton Formation At Isisford, Central-West Queensland, Australia, Inferred From Sandstone Concretions

“…The Isisford fossil fauna is dominated by aquatic and semi-aquatic animals, specifically large-bodied, fast-swimming predatory teleost fishes (ichthyodectiforms including Cladocyclus geddesi, and a possible halecomorphan (Faggotter et al 2007;Berrell et al 2014)), as well as small-bodied (< 1.5 m) basal eusuchian crocodyliforms (Isisfordia duncani (Salisbury et al 2006a)). Although smallto medium-size non-avian dinosaurs have also been discovered (but are yet to be described) (Fletcher et al 2009), the remains of larger sauropodan dinosaurs commonly found at other fossil sites within the Winton Formation (see Coombs et al 1981;Molnar 2001;Molnar et al 2005;Salisbury et al 2006b;Hocknull et al 2009;Poropat et al 2015aPoropat et al , 2015b are notably absent, despite over a decade of intense collecting. Also conspicuous by their absence are the remains of dipnoan lungfishes and turtles, which are also found at other Winton Formation fossil sites (see Molnar 1991;Dettmann et al 1992;Kemp 1997).…”

Articulated bone sets of manus and pedes of Camarasaurus (Sauropoda, Dinosauria)

“…Generally, the number of elements in the sauropod carpus decreases and appears to culminate in complete absence of ossified elements in titanosaurs (Borsuk-Bialynicka, 1977;Poropat et al, 2015a). Proximal carpals appear to be unossified in early sauropodomorphs and in the basal eusauropod Shunosaurus (Zhang, 1988;Benton et al, 2000;Remes, 2008;Sertich and Loewen, 2010), with the possible exception of the intermedium (e.g., in Jingshanosaurus xinwaensis and Seitaad ruessi; Remes, 2008;Sertich and Loewen, 2010).…”

“…It has often been hypothesized that the reduction of the sauropod carpus did not lead to only two ossified carpals in Camarasaurus or to the complete absence of carpal elements in certain titanosaurs, but that some of the primordially eleven elements remained cartilaginous during lifetime (Romer, 1956;Janensch, 1961;Borsuk-Bialynicka, 44 1977; Bonnan, 2003;Apesteguía, 2005;Poropat et al, 2015a). Other authors proposed that a thick layer of hyaline cartilage was enclosing the two bony carpals (Jensen, 1988;Wilson and Sereno, 1998).…”

“…However, mc I of Aragosaurus has a more D-shaped proximal articular surface, compared to Camarasaurus (Royo-Torres et al, 2014), and mc II of Aragosaurus bears a distinct tubercle on the distomedial ridge on the posterior surface, just proximal to the rugose articular facet (Royo-Torres et al, 2014, figure 12), which is absent in Camarasaurus. The length ratio between the metacarpals of a single manus is highly variable among genera (Poropat et al, 2015a), but also among different Camarasaurus specimens (Table 3). Whereas in SMA 0002, mc II is the longest and mc I the shortest of the series, other specimens exhibit a mc III that is longer than mc II (Ostrom and McIntosh, 1966;McIntosh, 2005), or a shorter or equally long mc V as mc I (Riggs, 1901;McIntosh, 2005).…”

“…Additionally, Gilmore's (1936) monograph on Apatosaurus and BorsukBialynicka's (1977) paper on Opisthocoelicaudia include adequate descriptions of manus and pes elements. Recently, several publications yielded additional important information on manual and pedal shape in sauropods (McIntosh et al, 1992(McIntosh et al, , 1996aAverianov et al, 2002;Bonnan, 2003Bonnan, , 2005Martínez et al, 2004;Apesteguía, 2005;Bedell and Trexler, 2005;Bonaparte et al, 2006;Harris, 2007;Läng and Goussard, 2007;González Riga et al, 2008;Curry Rogers, 2009;Hocknull et al, 2009;D'Emic et al, 2011;Nair and Salisbury, 2012;Poropat et al, 2015aPoropat et al, , 2015b.…”