Werneburg Ingmar, Hinz Juliane K, Gumpenberger Michaela, Volpato Virginie, Natchev Nikolay, Joyce Walter G
Fachbereich Geowissenschaften der Eberhard Karls Universität Tübingen, Tübingen, Germany; Museum für Naturkunde, Leibniz Institute for Research on Evolution and Biodiversity, Berlin, Germany; Paläontologisches Institut und Museum der Universität Zürich, Zürich, Switzerland.
J Exp Zool B Mol Dev Evol. 2015 May;324(3):230-43. doi: 10.1002/jez.b.22557. Epub 2014 Feb 4.
Turtles have the unparalleled ability to retract their heads and necks within their shell but little is known about the evolution of this trait. Extensive analysis of neck mobility in turtles using radiographs, CT scans, and morphometry reveals that basal turtles possessed less mobility in the neck relative to their extant relatives, although the anatomical prerequisites for modern mobility were already established. Many extant turtles are able to achieve hypermobility by dislocating the central articulations, which raises cautions about reconstructing the mobility of fossil vertebrates. A 3D-model of the Late Triassic turtle Proganochelys quenstedti reveals that this early stem turtle was able to retract its head by tucking it sideways below the shell. The simple ventrolateral bend seen in this stem turtle, however, contrasts with the complex double-bend of extant turtles. The initial evolution of neck retraction therefore occurred in a near-synchrony with the origin of the turtle shell as a place to hide the unprotected neck. In this early, simplified retraction mode, the conical osteoderms on the neck provided further protection.
海龟具有将头部和颈部缩进壳内的无与伦比的能力，但对于这一特征的进化却知之甚少。使用X光片、CT扫描和形态测量法对海龟颈部活动能力进行的广泛分析表明，尽管现代颈部活动的解剖学前提条件已经确立，但基干海龟相对于其现存亲属而言，颈部的活动能力较弱。许多现存海龟能够通过使中央关节脱臼来实现过度活动，这对重建化石脊椎动物的活动能力提出了警示。晚三叠世海龟原颚龟的三维模型显示，这种早期的基干海龟能够通过将头部侧向折叠到壳下的方式来缩回头部。然而，这种基干海龟中出现的简单腹外侧弯曲与现存海龟复杂的双弯曲形成了对比。因此，颈部缩回的最初进化与龟壳作为隐藏无保护颈部的地方的起源几乎是同步发生的。在这种早期的、简化的缩回模式中，颈部的锥形骨板提供了进一步的保护。
