Scheyer Torsten M, Sander P Martin
Institute of Palaeontology, University of Bonn, Nussallee 8, 53115 Bonn, Germany.
Proc Biol Sci. 2007 Aug 7;274(1620):1885-93. doi: 10.1098/rspb.2007.0499.
The palaeoecology of basal turtles from the Late Triassic was classically viewed as being semi-aquatic, similar to the lifestyle of modern snapping turtles. Lately, this view was questioned based on limb bone proportions, and a terrestrial palaeoecology was suggested for the turtle stem. Here, we present independent shell bone microstructural evidence for a terrestrial habitat of the oldest and basal most well-known turtles, i.e. the Upper Triassic Proterochersis robusta and Proganochelys quenstedti. Comparison of their shell bone histology with that of extant turtles preferring either aquatic habitats or terrestrial habitats clearly reveals congruence with terrestrial turtle taxa. Similarities in the shell bones of these turtles are a diploe structure with well-developed external and internal cortices, weak vascularization of the compact bone layers and a dense nature of the interior cancellous bone with overall short trabeculae. On the other hand, 'aquatic' turtles tend to reduce cortical bone layers, while increasing overall vascularization of the bone tissue. In contrast to the study of limb bone proportions, the present study is independent from the uncommon preservation of appendicular skeletal elements in fossil turtles, enabling the palaeoecological study of a much broader range of incompletely known turtle taxa in the fossil record.
晚三叠世基干龟类的古生态学传统上被认为是半水生的，类似于现代鳄龟的生活方式。最近，基于肢骨比例对这一观点提出了质疑，并有人提出龟类干群具有陆地古生态。在此，我们提供了独立的龟壳骨微观结构证据，证明最古老且最著名的基干龟类，即上三叠统的强壮原颌龟（Proterochersis robusta）和昆氏原鳄龟（Proganochelys quenstedti）栖息于陆地。将它们的龟壳骨组织学与现存偏好水生或陆地栖息地的龟类进行比较，清楚地显示出与陆地龟类分类群的一致性。这些龟类龟壳骨的相似之处在于具有发育良好的外部和内部皮质的板障结构、致密骨层的弱血管化以及内部松质骨致密且小梁总体较短的性质。另一方面，“水生”龟类往往会减少皮质骨层，同时增加骨组织的整体血管化。与肢骨比例研究不同，本研究独立于化石龟类中附属骨骼元素罕见的保存情况，从而能够对化石记录中更多知之甚少的龟类分类群进行古生态学研究。
