Why sauropods had long necks; and why giraffes have short necks

TL;DR

Sauropod dinosaurs evolved extremely long necks due to anatomical features like pneumatic bones and a lightweight head, unlike giraffes and other tetrapods, which lacked these adaptations.

Contribution

This paper explains the anatomical and evolutionary reasons behind the extreme neck length of sauropods compared to other long-necked animals.

Findings

Sauropods had necks up to 15 m long, six times longer than giraffes.

Key features enabling long necks include pneumatic bones and a lightweight head.

Non-sauropod long-necked animals lack critical adaptations for such elongation.

Abstract

The necks of the sauropod dinosaurs reached 15 m in length: six times longer than that of the world record giraffe and five times longer than those of all other terrestrial animals. Several anatomical features enabled this extreme elongation, including: absolutely large body size and quadrupedal stance providing a stable platform for a long neck; a small, light head that did not orally process food; cervical vertebrae that were both numerous and individually elongate; an efficient air-sac-based respiratory system; and distinctive cervical architecture. Relevant features of sauropod cervical vertebrae include: pneumatic chambers that enabled the bone to be positioned in a mechanically efficient way within the envelope; and muscular attachments of varying importance to the neural spines, epipophyses and cervical ribs. Other long-necked tetrapods lacked important features of sauropods, preventing the evolution of longer necks: for example, giraffes have relatively small torsos and large, heavy heads, share the usual mammalian constraint of only seven cervical vertebrae, and lack an air-sac system and pneumatic bones. Among non-sauropods, their saurischian relatives the theropod dinosaurs seem to have been best placed to evolve long necks, and indeed they probably surpassed those of giraffes. But 150 million years of evolution did not suffice for them to exceed a relatively modest 2.5 m.