Lennie Kendra I, Manske Sarah L, Mansky Chris F, Anderson Jason S
Biological Sciences, University of Calgary, 507 Campus Drive NW, Calgary, Alberta, Canada T2N 1N4.
McCaig Institute for Bone and Joint Health, University of Calgary, 3330 Hospital Drive NW, Calgary, Alberta, Canada T2N 4N1.
R Soc Open Sci. 2021 May 26;8(5):210281. doi: 10.1098/rsos.210281.
Evidence for terrestriality in early tetrapods is fundamentally contradictory. Fossil trackways attributed to early terrestrial tetrapods long predate the first body fossils from the Late Devonian. However, the Devonian body fossils demonstrate an obligatorily aquatic lifestyle. Complicating our understanding of the transition from water to land is a pronounced gap in the fossil record between the aquatic Devonian taxa and presumably terrestrial tetrapods from the later Early Carboniferous. Recent work suggests that an obligatorily aquatic habit persists much higher in the tetrapod tree than previously recognized. Here, we present independent microanatomical data of locomotor capability from the earliest Carboniferous of Blue Beach, Nova Scotia. The site preserves limb bones from taxa representative of Late Devonian to mid-Carboniferous faunas as well as a rich trackway record. Given that bone remodels in response to functional stresses including gravity and ground reaction forces, we analysed both the midshaft compactness profiles and trabecular anisotropy, the latter using a new whole bone approach. Our findings suggest that early tetrapods retained an aquatic lifestyle despite varied limb morphologies, prior to their emergence onto land. These results suggest that trackways attributed to early tetrapods be closely scrutinized for additional information regarding their creation conditions, and demand an expansion of sampling to better identify the first terrestrial tetrapods.
早期四足动物具有陆地生活特征的证据从根本上来说是相互矛盾的。归因于早期陆地四足动物的化石足迹比泥盆纪晚期的第一批身体化石早得多。然而，泥盆纪的身体化石显示出一种必须水生的生活方式。水生的泥盆纪类群与石炭纪早期可能为陆地生活的四足动物之间在化石记录上存在明显空白，这使得我们对从水到陆地的转变的理解变得更加复杂。最近的研究表明，在四足动物谱系中，必须水生的习性持续的程度比之前认为的要高得多。在此，我们展示了来自新斯科舍省蓝滩最早石炭纪时期的关于运动能力的独立微观解剖学数据。该地点保存了代表泥盆纪晚期到石炭纪中期动物群的类群的四肢骨骼以及丰富的足迹记录。鉴于骨骼会因包括重力和地面反作用力在内的功能压力而重塑，我们分析了骨干中部的致密性剖面和小梁各向异性，后者采用了一种新的全骨方法。我们的研究结果表明，早期四足动物在登上陆地之前，尽管四肢形态各异，但仍保持着水生生活方式。这些结果表明，对于归因于早期四足动物的足迹，应仔细审查以获取有关其形成条件的更多信息，并且需要扩大采样范围以更好地识别第一批陆地四足动物。
