Pelorosaurus, BECKLESII, Mantell, 1850

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

‘ PELOROSAURUS ’ BECKLESII ( MANTELL, 1852)

The complex history of the genus ‘ Pelorosaurus ’ is discussed elsewhere ( Naish & Martill, 2001; Upchurch et al., 2004). ‘ Pelorosaurus ’ becklesii comes from the Barremian Wessex Formation, UK, and consists of a humerus, radius, ulna, and some skin impressions. Upchurch (1995) suggested that ‘ Pelorosaurus ’ becklesii was an early titanosaur on the basis of its proximally curved anteromedial process of the ulna and the presence of polygonal plates similar to those of the titanosaur Saltasaurus in its skin. However, a similarly curved anteromedial process of the ulna and raised olecranon process are also found in non-titanosaurs (e.g. Giraffatitan , Sauroposeidon ; pers. observ. of YPM 326, a cast of ‘ Pelorosaurus ’ becklesii; Fig. 7 ) and should not be treated as a titanosaur synapomorphy in the absence of a cladistic analysis. Since the assessment of Upchurch (1995), similar polygonal dermal patterns have been reported in non-titanosaurs (e.g. Tehuelchesaurus, Giménez, 2007 ). Furthermore, ‘ Pelorosaurus ’ becklesii lacks one unambiguous synapomorphy of the clade uniting Chubutisaurus + Titanosaura: an undivided notch on the humeral radial condyle. ‘ Pelorosaurus ’ becklesii probably represents a titanosauriform on the basis of the anteromedial arm of the ulna being much longer than its anterolateral arm, but its titanosaur affinities cannot be substantiated at present.

Figures

Figure 7. Purported early ‘titanosaur’ species in comparison with a basal titanosauriform (Giraffatitan). The caudal vertebral procoely of ‘Iuticosaurus’ and curved/raised ulnar olecranon of ‘Pelorosaurus’ becklesii are indistinguishable from the situation in Giraffatitan. Scale bars: Giraffatitan vertebra = 5 cm; ‘Iuticosaurus’, Giraffatitan ulna, and ‘Pelotosaurus’ becklesii = 10 cm.