Birbal Sahni Institute of Palaeobotany, 53 University Road, Lucknow 226007, India.
Birbal Sahni Institute of Palaeobotany, 53 University Road, Lucknow 226007, India.
Eur J Protistol. 2014 Feb;50(1):89-105. doi: 10.1016/j.ejop.2013.05.003. Epub 2013 Jul 19.
The evolutionary history of thecamoebians (testate amoebae) extends back to the Neoproterozoic Era. However, until now, these have had a restricted, discontinuous and modest record across the world. The studied sediment of Raniganj Formation (Godavari Graben), Andhra Pradesh, India has been assigned as Late Permian on the basis of co-occurring age-diagnostic Late Permian palynomorphs. About sixteen thecamoebian species and one taxon incertae sedis have been recorded here in the palynological slides on the basis of shell morphology and morphometry. Out of these, five belong to the family Arcellidae, seven to Centropyxidae, two to Trigonopyxidae, one to Difflugiidae, one to Plagiopyxidae, and one is regarded incertae sedis. The morphometric characteristics of fossil forms resemble their corresponding extant species studied from ecologically diverse fresh water wetlands in India. In general, the ratio of shell diameter and aperture diameter of Late Permian fossil and extant specimens show significant correlation in all the studied species. Except that, the ratio of shell length and breadth is the distinguishing feature between Centropyxis aerophila and C. aerophila 'sylvatica', rather than the ratio of shell length and longest diameter of the shell aperture in both fossil and extant forms. The study elucidates the minimal morphological evolution in thecamoebians and their survival during mass extinction periods and stressful environmental conditions over the geological timescale.
裸变形虫（有壳变形虫）的进化历史可以追溯到新元古代。然而，直到现在，这些在世界范围内的记录都受到限制、不连续且有限。印度安得拉邦拉尼根杰组（戈达瓦里地堑）的研究沉积层是根据共生的晚二叠世年龄诊断的孢粉来确定为晚二叠世的。在孢粉薄片上，根据壳形态和形态测量学，这里记录了大约 16 种有壳变形虫物种和一个分类地位不确定的分类单元。其中，有 5 种属于胶结虫科，7 种属于 Centropyxidae，2 种属于 Trigonopyxidae，1 种属于 Difflugiidae，1 种属于 Plagiopyxidae，还有 1 种分类地位不确定。化石形态的形态特征与在印度生态多样的淡水湿地中研究的相应现代物种相似。一般来说，晚二叠世化石和现代标本的壳直径与壳口直径的比值在所有研究的物种中都显示出显著的相关性。此外，壳长与壳宽的比值是 Centropyxis aerophila 和 C. aerophila 'sylvatica 之间的区别特征，而不是化石和现代形式中壳长与壳口最长直径的比值。这项研究阐明了裸变形虫的最小形态进化以及它们在地质时间尺度上的大灭绝时期和恶劣环境条件下的生存能力。
