The study of paleoecology involves the fossil record and paleoenvironmental information of many kinds of organisms. Fossils preserved in strata usually have a certain relation with each other. It is an important means to understand the biological evolution and its environmental background to carry out multi-scaled comprehensive analysis and study on a variety of fossils preserved together.
Recently, the Early Land Plant working group of Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences (NIGPAS), led by Prof. XU Honghe, conducted a systematic paleoecological study based on plant fossils from the Lower Devonian of Guangxi. The related research results were published in an open-accessed journal of iScience.
Testate amoebae are a group of widespread microcosmic protists and play a crucial part in Earth’s biosphere. Testate amoebae stand out with their unique test (shell), usually 20–150 μm in size, and in the tree of eukaryotic life, are known as a polyphyletic group that consists of three unrelated taxonomic lineages. As free-living protists, extant testate amoebae are distributed in most kinds of freshwater or terrestrial habitats, e.g., river, pond, peat land and soil, but as well as in brackish and marine waters, and are of great significance to the flow of matter and energy in ecosystems.
It has been generally considered that the evolutionary history of testate amoebae could be traced back to the late Tonian (early Neoproterozoic, ca. 800–720 Ma), as evidenced by the extensive records of marine vase-shaped microfossils in this period. However, not much is known about the Paleozoic testate amoeba fossils, as of now. The oldest unambiguous occurrence of Paleozoic testate amoebae is a freshwater arcellinid species from the Lower Devonian Rhynie chert followed by scattered reports from the upper Carboniferous and Permian. There is also rare knowledge about the internal structures of fossil testate amoebae. Except few possible reproductive cells or resting cysts in phosphatized or amber-preserved specimens. There were no any other bio-related structures inside the shells of fossil testate amoebae have been observed.
In this study, a shallow-marine testate amoebae is firstly discovered as exquisitely preserved vase-shaped microfossils from the Lower Devonian Cangwu Formation in Guangxi, southwestern China, and based on morphological characters, interpret them as a new fossil species of arcellinid testate amoebae. Additionally, it is shown that distinct acetabuliform structures are preserved in the shell of these testate amoeba, and infers possible sources of these internal structures.
“Our testate amoeba co-occurs with several types of plant remains, e.g. Zosterophyllum sinense and some rhyniophytoids, and more recently reported Houia (Euchelicerata)”,XU says, “it can be suggested that the fossil-bearing horizon represents a shallow-water marine environment.” These fossils extend the record of marine vase- shaped microfossils into the Early Devonian, during which the earliest freshwater testate amoebae occurred. Recent advances in molecular phylogeny and microbial paleobiology of testate amoebae raise a scenario that, within Arcellinida lineages, the marine-freshwater transition probably occurred multiple times and only during the Phanerozoic. That arcellinids occurred in both the freshwater and shallow-marine environments in the Early Devonian concurs with the very possibility.
This work is a contribution to the Deep-time Digital Earth (DDE) Big Science Program.
Reference: Wang K, Xu H-H*, Liu B-C, Bai J, Wang Y, Tang P, Lu J-F, Wang Y. 2023. Shallow-marine testate amoebae with internal structures from the Lower Devonian of China. iScience. 26(5), 106678. https://doi.org/10.1016/j.isci.2023.106678.
Fig 2 Three-dimensional reconstruction of Cangwuella ampulliformis from the Lower Devonian Cangwu Formation, based on synchrotron radiation X-ray tomography.
Contact:
LIU Yun, Propagandist
Email: yunliu@nigpas.ac.cn
Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences
Nanjing, Jiangsu 210008, China
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