Department of Earth Sciences , University of Bristol , Bristol , England.
PeerJ. 2013 Feb 12;1:e36. doi: 10.7717/peerj.36. Print 2013.
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 their necks probably surpassed those of giraffes. But 150 million years of evolution did not suffice for them to exceed a relatively modest 2.5 m.
蜥脚类恐龙的颈部长达 15 米：比世界记录的长颈鹿长六倍，比所有其他陆地动物长五倍。几个解剖学特征使得这种极端伸长成为可能，包括：绝对大的体型和四足姿势为长脖子提供了一个稳定的平台；一个小而轻的头部，不进行口腔食物处理；颈椎数量众多且单独伸长；高效的基于气囊的呼吸系统；以及独特的颈椎结构。蜥脚类恐龙颈椎的相关特征包括：使骨骼能够在机械上有效定位在信封内的充气腔室；以及对神经棘、副突和颈椎肋骨的重要程度不同的肌肉附着。其他长颈四足动物缺乏蜥脚类恐龙的重要特征，阻止了更长颈部的进化：例如，长颈鹿的躯干相对较小，头部较大且较重，与通常的哺乳动物一样仅具有七个颈椎，并且缺乏气囊系统和充气骨骼。在非蜥脚类恐龙中，它们的兽脚亚目恐龙亲戚似乎最有能力进化出长脖子，事实上它们的脖子可能超过了长颈鹿的脖子。但是，1.5 亿年的进化还不足以使它们的脖子超过相对适中的 2.5 米。
