  Although the sauropod dinosaurs have been recognised for more than a hundred
and sixty years, much remains to be discovered and understood about their
functional anatomy and palaeobiology. Older taxa require revision and new taxa
await description. The characteristic long necks of sauropods are mechanically
perplexing and their evolution is obscure. All these issues are addressed
herein.
  The genus Brachiosaurus is represented by the American type species B.
altithorax and the better known African species B. brancai. However,
examination of the overlapping material shows 26 differences between the
species. B. brancai must be removed from Brachiosaurus and referred to the
genus Giraffatitan, which has been previously proposed for it.
  Xenoposeidon proneneukos is a new neosauropod from the Lower Cretaceous
Hastings Bed Group, known from a single partial dorsal vertebra. The excellent
preservation of the Xenoposeidon holotype reveals six unique characters. The
distinctive morphology suggests that Xenoposeidon may represent a new sauropod
family, extending sauropod disparity as well as bringing to four the number of
sauropod families known from the Wealden.
  A second new Early Cretaceous genus is also described, a titanosauriform from
the Ruby Ranch Member of the Cedar Mountain Formation, in Utah. This taxon is
known from at least two individuals, an adult and a juvenile, which together
provide vertebrae, ribs, a scapula, sternal plates and an ilium. The ilium is
particularly unusual, exhibiting five unique features.
  The longest sauropod necks were five times as long as those of the next
longest terrestrial animals, and four separate lineages evolved necks exceeding
10 m. Elongation was enabled by sheer size, vertebral pneumaticity and the
relative smallness of sauropod heads, despite aspects of cervical osteology
that are difficult to understand on mechanical first principles.
