Brontomerus mcintoshi

D, Michael D. & Emic, 2012, The early evolution of titanosauriform sauropod dinosaurs, Zoological Journal of the Linnean Society 166 (3), pp. 624-671 : 646-647

BRONTOMERUS MCINTOSHI

( TAYLOR, WEDEL & CIFELLI, 2011)

Brontomerus was named on the basis of dissociated material consisting of an ilium, scapula, distal caudal vertebra, ribs, and other fragmentary bones ( Taylor et al., 2011: table 3) from the Early Cretaceous Burro Canyon Formation (equivalent to the Ruby Ranch Member of the Cedar Mountain Formation) of Utah. As (1) the material is disarticulated, (2) there is substantial size variation amongst the known elements in the quarry, and (3) no elements from the quarry overlap with the holotype (an ilium), referral of material from the holotypic quarry to Brontomerus is weak. Thus, the diagnosis of the species rests on the holotypic ilium ( Taylor et al., 2011). Five autapomorphies were presented for the holotype of Brontomerus : (1) ischial peduncle reduced to very low bulge; (2) preacetabular lobe directed anterolaterally but not curved; (3) ilium height 52% of total length; (4) preacetabular lobe 55% of total ilium length; (5) postacetabular lobe reduced to near absence. The first two characters are present in a variety of taxa (e.g. Tastavinsaurus, Royo-Torres, 2009 ; Giraffatitan, Janensch, 1961 ).

The latter three characters cannot be evaluated in Brontomerus because the postacetabular process is broken – although Taylor et al. (2011: 81) described this as a ‘genuine osteological feature not related to damage’, it is clear that this margin is not complete, and the reconstruction of the posterior curvature of the ilium is arbitrary. When reconstructed with a postacetabular process similar to that in other sauropods, the ilium of Brontomerus is similar to those of brachiosaurids (e.g. Giraffatitan, Janensch, 1961 : pl. E). Because of its problematic diagnosis, Brontomerus mcintoshi represents a nomen dubium. Some of the material referred to Brontomerus by Taylor et al. (2011) appears to pertain to Titanosauriformes based on the presence of pneumatic dorsal ribs or coarse camellate vertebral pneumaticity.

* Qingxiusaurus also shares the presence of a posteriorly expanded sternal plate (character 76) with Alamosaurus and Malawisaurus . This is recovered as a lithostrotian synapomorphy under accelerated transformation.

Age abbreviations: EK, Early Cretaceous; LJ, Late Jurassic; LK, Late Cretaceous.

Area abbreviations: AF, Africa; AS, Asia; AU, Australia; EU, Europe; NA, North America; SA, South America.

Clade/validity abbreviations: mdb, more derived brachiosaurids; mde, more derived euhelopodids; mdso, more derived somphospondylans, nd, nomen dubium; TSF, titanosauriform.