BRACHIOSAURIDAE (Riggs, 1903)

D, Michael D. & Emic, 2012, The early evolution of titanosauriform sauropod dinosaurs, Zoological Journal of the Linnean Society 166 (3), pp. 624-671 : 640-641

BRACHIOSAURIDAE

This analysis recovered six taxa as brachiosaurids, more than any other analysis to date. The fragmentary and often non-overlapping anatomy of putative brachiosaurids (e.g. Cedarosaurus ) has yielded limited taxonomic breadth and/or resolution for this clade in previous analyses (e.g. Upchurch et al., 2004; Rose, 2007; Ksepka & Norell, 2010), although many taxa were suggested to be brachiosaurids without a cladistic analysis. In particular, cranial data are known for only three brachiosaurids ( Abydosaurus , Europasaurus , Giraffatitan ), and the only brachiosaurid for which ACCTRAN, accelerated transformation; DELTRAN, delayed transformation; mdb, more derived brachiosaurids; mde, more derived euhelopodids; mdso, more derived somphospondylans.

Italicization indicates characters that have ambiguous changes in other parts of the cladogram that are instead because of missing data ( Table 5). Plus signs indicate gains, minus signs indicate losses.

substantial cranial and postcranial data are available is Giraffatitan .

The traditional (noncladistic) content of the Brachiosauridae was maintained by this analysis (i.e. Brachiosaurus , Giraffatitan ). In addition, the affinities of several putative brachiosaurids were confirmed by this analysis, including Cedarosaurus , Venenosaurus , and Abydosaurus . In contrast, some putative brachiosaurids [ Atlasaurus , Sauroposeidon (including ‘ Paluxysaurus ’), Qiaowanlong ] were recovered outside the clade, and some likely brachiosaurids (‘French’ Bothriospondylus , Sonorasaurus ) were not included in this analysis (but see ‘Fragmentarily represented taxa’ below). Five unambiguous brachiosaurid synapomorphies were recovered (wide supratemporal fenestrae, ventral triangular projection on anterior ramus of quadratojugal, maxillary teeth twisted axially, dorsal vertebrae with ‘rod-like’ transverse processes, ischium with abbreviate pubic peduncle) as well as eight more under ACCTRAN ( Tables 5, 6). Under DELTRAN, these eight synapomorphies optimize either as synapomorphies of Giraffatitan plus more derived brachiosaurids, an autapomorphy of Giraffatitan , or as multiple gains and losses amongst various titanosauriforms.

Europasaurus was recovered as the basal-most brachiosaurid, in contrast to previous hypotheses that suggested that it was a basal macronarian ( Sander et al., 2006). Although strongly supported as a brachiosaurid, the affinities of Europasaurus within that clade are labile given the data at hand. The basal position of Europasaurus within the Brachiosauridae may be strongly influenced by missing data, because many of the synapomorphies that unite more derived brachiosaurids could not be scored for Europasaurus given that those aspects of its anatomy are unknown or undescribed (e.g. lacrimal, metatarsal IV, caudal vertebrae).

Giraffatitan and Brachiosaurus , once considered congeneric (e.g. Janensch, 1950), are recovered as successively more derived brachiosaurids in this analysis ( Fig. 5 ). Only a few steps are required to move Brachiosaurus into a more or less derived position within Brachiosauridae or as the sister taxon of Giraffatitan as traditionally hypothesized ( Janensch, 1950; Taylor, 2009). Future, confident referrals of material to Brachiosaurus altithorax are needed to understand better its phylogenetic position. Cedarosaurus , Venenosaurus , and Abydosaurus , all known from the Early Cretaceous of North America, are recovered in a polytomy as the most derived brachiosaurids. This result is in keeping with the original descriptions and other cladistic analyses dealing with these taxa ( Tidwell et al., 1999; Upchurch et al., 2004; Rose, 2007; Chure et al., 2010).

Figures

Figure 5. Cladistic hypothesis presented in this study. The cladogram is a strict consensus of nine equally parsimonious trees. Clade names as defined by phylogenetic taxonomy (Table 1; Wilson & Upchurch, 2003) are listed beside each node.