New freshwater arthropod, Maldybulakia saierensis sp. nov., from the Silurion of the western Junggar, northwest China. The discovery of this species brings forward the earliest appearance of the Maldybulakia, previously known from the Devonian of Kazakhstan and eastern Australia, to the late Silurian. It is the oldest body fossil record of a putatively freshwater arthropod outside Laurussia, and greatly expands their palaeogeographical distribution.
The research results were published in Papers in Palaeontology, an international journal of professional palaeontology.
Compared to marine life or marine ecosystems in the early and middle Palaeozoic, the understanding of nonmarine communities in this period is poor, an important reason being the rarity of the fossil record of early freshwater and terrestrial organisms, especially animals. Although the oldest land on Earth and life on it date to the Precambrian, terrestrial life during this time largely consists of microbes.
Arthropods, the most species-rich animal phylum, mainly inhabited marine or transitional environments before the Silurian. Molecular clock estimates suggest that the terrestrialization of arthropods commenced in the Cambrian to Ordovician, but the trace fossil record suggests that freshwater arthropods may have existed in the Ordovician, and amphibious trackways on tidal flats and coastal dunes are known even earlier, in the Cambrian. However, freshwater and/or terrestrial arthropods (represented by the Myriapoda and trigonotarbid arachnids) with undisputed body fossil evidence did not appear before the middle to late Silurian. Silurian freshwater and/or terrestrial arthropods are known mainly from southern Laurussia, represented by England and Scotland. By the Early Devonian their fossil record and diversity increased significantly, and the palaeogeographical distribution extended to other plates/terranes.
Recently, new insights into the origin and evolution of early non-marine were given by a joint working group of Prof. XU Honghe, WANG Yi, and graduate LIU Bingcai from Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences (NIGPAS), Associate Prof. ZONG Ruiwen, and gradutes YIN Jiayi and MA Juan from China University of Geoscience (Wuhan), and Prof. Gregory D. Edgecombe from Natural History Museum (London, United Kindom).All fossils were collected from the volcanic and/or pyroclastic rocks occurring widely in the Palaeozoic strata in western Junggare Basin, Xinjiang during the work of plant fossil field work in October of 2020. With the evidence of plant fossils yielded from the same bed, and more recent zircon geochronology studies, during which petrologists have conducted a large number of zircon geochronology studies on the volcanic (or pyroclastic) rocks in this volcanic arc and the magmatic rocks intruded into the strata, and obtained zircon ages for these volcanic or pyroclastic rocks, which were originally classified as Devonian, as now being Silurian, c. 436–420 Ma. “The age of our fossils is determined as the Pridoli of the Silurian”, says XU.
The evident morphological differences between different species of Maldybulakia, and the discovery of them on both sides of the Palaeo-Tethys Ocean, suggest that Maldybulakia may have a vicariant origin or that land bridges in the Palaeo-Tethys Ocean provided migration channels for Maldybulakia.
“In the middle and late Silurian, freshwater arthropods are now known from multiple plates/terranes, indicating that arthropods were already distant from the sea and were exploiting terrestrial ecological niches during this period,” XU says, “it also suggests that freshwater arthropods may have first appeared in the early Silurian or even earlier, as suggested by fossil calibrated molecular time trees.”
Reference: Zong, R. W.*, GD. Edgecombe, Liu, B. C., Wang, Y., Yin, J. Y., Ma, J., Xu, H. H.*, 2023. Silurian freshwater arthropod from northwest China. Papers in Palaeontology, e1488. https://doi.org/10.1002/spp2.1488.
Fig.1 Collecting arthropod and plant fossils in the fieldwork.
Fig.2 Deferent sclerites of Maldybulakia saierensis from the Silurian of Xinjiang.
Fig.3 Reconstructed arrangement of sclerites of Maldybulakia saierensis from the Silurian of Xinjiang.
Fig.4 Spores and plant fragments co-bearing with Maldybulakia saierensis from the Silurian of Xinjiang.
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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