Giraffatitan brancai (Janensch, 1914)

D, Michael D. & Emic, 2012, The early evolution of titanosauriform sauropod dinosaurs, Zoological Journal of the Linnean Society 166 (3), pp. 624-671 : 634

GIRAFFATITAN BRANCAI

Riggs (1903) coined the name Brachiosaurus altithorax for what was then the world’s largest-known dinosaur. Brachiosaurus altithorax was founded on a single partial skeleton from the Late Jurassic Morrison Formation of Colorado, USA, represented by several dorsal vertebrae, a sacrum with ilia, two caudal vertebrae, a coracoid, humerus, femur, and some dorsal ribs. Some other materials from the Morrison Formation may belong to Brachiosaurus altithorax (see review in Taylor, 2009), but many of these materials do not overlap anatomically with the holotype, and those materials that do overlap have not currently been united with the holotype using autapomorphies. Consequently, scoring for Brachiosaurus altithorax is limited to the holotype.

Janensch (1914) named two additional species of Brachiosaurus from the Late Jurassic Tendaguru beds of Tanzania, Brachiosaurus brancai and Brachiosaurus fraasi , which were later synonymized by Janensch (1929). Paul (1988) proposed that the Tanzanian form be regarded as a separate subgenus, Brachiosaurus (Giraffatitan) brancai , which Taylor (2009) formalized by referring the Tanzanian brachiosaur material to a separate genus, Giraffatitan brancai . Many of the differences cited by Taylor (2009) do not differ substantially between the Morrison and Tendaguru specimens when serial and individual variation are taken into account [e.g. caudal vertebral neural spine shape; compare Taylor (2009: fig. 3) with Ikejiri et al. (2005: fig. 5)]. In addition, some of the differences cited in support of generic separation of the Morrison and Tendaguru brachiosaurids are erroneous owing to misinterpretation of broken or deformed features (e.g. the cited tubercle on the posterior ilium of Brachiosaurus altithorax is a fragment of a sacral rib; the cited block-like hyposphene of the caudal vertebrae of Brachiosaurus altithorax is the broken remainder of the postzygapophyses; pers. observ.), or have a wider distribution amongst sauropods (e.g. the laterally deflected coracoid glenoid; see Wilson & Sereno, 1998). However, several features suggested by previous authors ( Janensch, 1950; Paul, 1988; Taylor, 2009) do distinguish the Tendaguru and Morrison brachiosaurid exemplars in a substantive way. The following features do not vary within other sauropod genera when deformation, breakage, within-individual, and within-species sources of variation are accounted for: the centra of dorsal vertebrae are broader transversely than dorsoventrally in Giraffatitan brancai , rather than subcircular in cross-section in B. altithorax ; anterior caudal vertebrae are about 30% taller relative to centrum length in Brachiosaurus altithorax ; transverse processes are only half of the neural spine length in the posterior dorsal vertebrae of Brachiosaurus altithorax , whereas they are subequal to neural spine length in Giraffatitan brancai ( Janensch, 1950; Paul, 1988; Taylor, 2009). These three features justify the generic separation of Giraffatitan and Brachiosaurus . Consequently, the name Giraffatitan brancai will be used to refer to the hypodigm brachiosaur material from Tendaguru.