Aspects of the history, anatomy, taxonomy and palaeobiology of sauropod dinosaurs

TL;DR

This paper reviews sauropod dinosaur history, anatomy, taxonomy, and palaeobiology, describing new taxa, revising classifications, and discussing the evolution of their long necks and functional adaptations.

Contribution

It introduces new sauropod taxa, revises the classification of Brachiosaurus and Giraffatitan, and provides insights into sauropod neck evolution and diversity.

Findings

Brachiosaurus brancai should be reclassified as Giraffatitan.

Xenoposeidon is a new genus potentially representing a new sauropod family.

Sauropod necks could reach over 10 meters, evolved in multiple lineages.

Abstract

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.