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Journal of Paleontology 90(1):102–132


ventral faces. There are no ventrolateral ridges connecting anterior and posterior chevron facets as in some titanosauri- forms (e.g., Huabeisaurus,D’Emic et al., 2013). Chevron facets have been over-prepared (i.e., mechanically removed during preparation, exposing interior bone) in several vertebrae, so their height relative to the rest of the vertebra is unknown (Fig. 10). Centra are relatively constant in length throughout the ser- ies (Table 1). The anteriormost preserved centrum in the series (ASDM 500-6) has damaged anterior and posterior faces. Cen- tra of other vertebrae that are more anteriorly positioned in the series have anteriorly concave and posteriorly flat faces (e.g., ASDM 500-7, -8, -294), as in many non-lithostrotian sauropods (D’Emic, 2013). Centra of vertebrae that are more posteriorly positioned in the series have equally concave anterior and pos- terior faces (e.g., ASDM 500-10). Transverse processes of more anterior caudal vertebrae are blade–like and curve posteriorly to project past the posterior margin of the centrum, whereas transverse processes of more posterior caudal vertebrae are simple tubercles (Fig. 10.6). The postzygapophyses are ante- roposteriorly elongate and project abruptly from of the neural spine posteriorly along with posterior reduction of the SPOL, a feature interpreted as an autapomorphy of Lusotitan (Mannion et al., 2013) that is present in Cedarosaurus, Giraffatitan, and several other sauropods as well. The prezygapophyses and neural spine are incomplete or missing in all of the caudal ver- tebrae, but a shallow ridge and fossa are present anterior to the postzygapophyses on two of the better preserved-vertebrae (ASDM 500-10, -296). This ridge and fossa were described as an autapomorphy of Lusotitan by Mannion et al. (2013), but this feature has a broader distribution among sauropods (see below).


could we find more than two small fragments of the scapular blade. The two fragments indicate that the blade was broadly D-shaped in cross-section proximally and flatter distally (Fig. 11).


Scapula.—A partially complete scapula was reported and figured by Thayer and Ratkevitch (1995:fig. 6), but we could not find a bone matching that depicted in the field photograph, nor


Humerus.—The right humerus is missing most of its proximal end and its midshaft is damaged (Fig. 12). Based on compar- isons with the humerus of Brachiosaurus and the 2:3 radius: humerus length ratio common in sauropods (MDD, personal observation), it would have been around 150cm long when complete (Table 2). Near its midshaft the humerus measures 16.8cm transversely by 12.2cm anteroposteriorly, with a circumference of approximately 47.5 cm. The humerus is elongate (estimated midshaft circumference/estimated total L =0.32). The lateral margin of the humerus is nearly straight,


whereas the medial margin is bowed. The deltopectoral crest is incomplete and slightly curves medially. The proximolateral corner of the bone and the presence of a raised attachment site in the deltopectoral fossa for the supracoracoideus cannot be assessed due to damage. No ridges or tubercles are present on the posterolateral face of the bone, unlike the condition observed in most titanosaurs (Upchurch et al., 2004; Wilson et al., 2009). The distal end of the humerus was misidentified as that of a


femur by Ratkevitch (1998) and the distal metaphyseal circumference of the humerus was cited as the midshaft circumference of the femur in Benson et al. (2014). It has a well-developed, divided radial condyle that projects anteriorly from the bone. The ulnar condyle is muted anteriorly, but forms a sharp, slightly acute angle posteriorly. The ulnar condyle is especially developed into a triangular process that projects very far posteriorly when compared with most other sauropods, which is interpreted as an autapomorphy of Sonorasaurus convergently acquired in derived titanosaurs (Figs. 13, 8).


Figure 11. Parts of the cross sections of the blade of the holotypic scapula of Sonorasaurus thompsoni (ASDM 500) from the mid-Cretaceous Turney Ranch Formation of Arizona, USA.


Figure 12. Right holotypic humerus of Sonorasaurus thompsoni (ASDM 500) from the mid-Cretaceous Turney Ranch Formation of Arizona, USA: (1) anterior; (2) posterior; (3) distal views, with cross section of shaft shown between (A) and (B). Abbreviations: div = divided radial condyle; trp = posteriorly projecting triangular process.


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