D’Emic et al.—Revision of the sauropod dinosaur Sonorasaurus


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Figure 9. Dorsal vertebrae of Sonorasaurus thompsoni (ASDM 500) from the mid- Cretaceous Turney Ranch Formation of Arizona, USA: Two dorsal vertebrae in (1) right lateral view that are cemented together taphonomically; (2) partial dorsal vertebral centrum in posterior view; (3) same in anterior view; (4) dorsal vertebral neural arch in posterior view; (5) same in right lateral view; (6) same in dorsal view. Abbreviations: acpl = anterior centroparapophyseal lamina; cam = camera; hypa = hypantrum; hypo = hyposphene; pcdl = posterior centrodiapophyseal lamina; pcpl = posterior centroparapophyseal lamina; podl = postzygodiapophyseal lamina; posdf, postzygapophyseal spinodiapophyseal fossa; spol = spinopostzygapophyseal lamina.


it comes from about 0.6km away in a different stratum of the Turney Ranch Formation (R. Thompson, personal communica- tion, 2014).


Diagnosis.—Sonorasaurus thompsoni is nested within


Brachiosauridae based on very elongate forearm long bones (as a local autapomorphy of a subset of brachiosaurids; see Discussion below) and distally beveled metatarsal IV (D’Emic, 2012; see Cladistic analysis below). Autapomorphic features are (1) the extreme posterior development of the ulnar condyle of the humerus into a triangular process and (2) a funnel-shaped but gracile metatarsal V (proximal breadth/length = 0.6).


Occurrence.—Sonorasaurus thompsoni was found in the Turney Ranch Formation of the Bisbee Group, in Mattie Canyon near the Whetstone Mountains, southern Arizona, USA. In an effort to constrain maximumdepositional age for the Sonorasaurus holotype, detrital zircons were separated from two sedimentary beds within the holotype quarry (the “clay-ash beds” and bed “2” adjacent to the bone bearing bed [“3”]of Scarborough, 2000:fig. 2; both of which are within approxi- mately 1m of the holotype in a stratigraphic sense). For details on our radiometric dating methods and results, see “Geology of the Turney Ranch Formation” below, as well as Figure 2 and Supplemental Data 1. The weighted mean average, with a


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