Fulu Biota, a New Exceptionally Preserved Cambrian Fossil Assemblage from the Longha Formation in Southeastern Yunnan

Fulu biota, a new exceptionally preserved Cambrian fossil assemblage from the Longha Formation in southeastern Yunnan Shanchi Penga, b*, Xianfeng Yangc, Liu Yuc, Xuejin Zhua, b, Haijing Sund, Samuel Zamorae, Yingyan Maoa, and Yuchen Zhanga aState Key Laboratory of Palaeobiology and Stratigraphy (Chinese Academy of Sciences), Nanjing 210008, China bNanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China cYunnan Key Laboratory for Palaeobiology, Yunnan University, Kunming 650091, ChinaeNational Maritime Museum of China, Tianjin 300467, China dNational Maritime Museum of China, Tianjin 300467, China eInstituto Geológico y Minero de España, C/ Manuel Lasala, 44 - 9º B, 50006 Zaragoza, Spain Abstract A new exceptionally preserved Cambrian biota, with fossils belonging to multiple phyla, has recently been found from the middle part of the Longha Formation, near Fulu Village, southeastern Yunnan, South China, and is named the Fulu biota. Groups recovered so far include polymerid trilobites, agnostoids, large bivalved arthropods, bradoriid arthropods, echinoderms, brachiopods, priapulids (worms), hyoliths, macroscopic algae, and trace fossils. The arthropods dominate and are highly diverse with echinoderms second in diversity. The associated agnostoids provide a precise late Guzhangian Age (late Miaolingian Epoch) for the biota, indicating that the biota occurs stratigraphically about halfway between the occurrences of the Kaili and the Guole biotas of South China, from both of which the new Fulu biota differs significantly in faunal components. Guzhangian biotas preserving poorly mineralized tissues and complete echinoderms were previously unknown in Gondwana until now, providing a unique window into life at this critical time interval. Keywords: Fulu biota; Fossils of multiple phyla; Longha Formation; Guzhangian; Yunnan, South China 1. Introduction We report the discovery of an important new fossil biota, the Fulu biota, that shows exceptional preservation of some invertebrate groups at a critical but poorly known time interval – the “late” Cambrian. It is also located in the southeastern corner of Yunnan Province at a much younger horizon than the famous Chengjiang and Guanshan biotas, both of which are in eastern Yunnan and are early Cambrian in age (Hou et al., 2004, 2017; Hu et al., 2013). Until the Fulu biota was discovered, there were only two of such biotas found from the upper half of the Cambrian of China, the Kaili biota from basal Miaolingian Series (Zhao, 2011) in eastern Guizhou Province and the Guole biota from middle Furongian Series in western Guangxi Province (Zhu et al., 2016), occuring at about 508 Ma and 491.5 Ma respectively. As the third exceptionally preserved biota from upper half of Cambrian in China, the Fulu biota which is from upper Guzhangian Stage at about 498.5 Ma in age, is sandwiched stratigraphically between the older Kaili biota and the younger Guole biota, close to the halfway, and therefore fills an important gap in the knowledge of Cambrian faunas (Fig.1). This deposit is also of comparable age to the important “orsten” fauna of Scandinavia, and the Weeks Formation of North America, providing an opportunity to compare contemporary faunas from different environments, paleocontinents, and styles of preservation. [Figure 1 is about here] Figure 1. Global and Chenese chronstratigraphic subdivisions of Cambrian System and stratigraphic positions of Cambrian major fossil Lagerstätten (solid stars) and the new Fulu lagerstätte (open star). Fm. = Formation; Sh. = Shale. 2. Locality and Geological Setting As a natural outcrop on the north side of the Y028 rural highway, the fossil site of the new exceptionally preserved Fulu biota lies about 1 km northwest of Fulu Village (Fig. 2D) or about 15 km southeast of the Tianpeng Township (Fig. 2C, D). From either Fulu or Tianpeng, the Y028 highway leads to the fossil locality. The Cambrian outcrop widely in Tianpeng-Fulu area, which lies at the southeastern corner of Yunnan Province, and exclusively consists of Cambrian formations belonging to upper half of the system, i.e. Miaolingian and Furongian series. No pre-Miaolingian succession are known from this area. The Tianpeng-Fulu area is regarded as one of the classical areas in Yunnan for the Cambrian stratigraphic studies, known as the Funing Stratigraphic Subregion of the Southeast Yunnan Startigraphic Region (Luo et al., 2009), and holds a number of lithostratigraphic unit stratotypes of formations that include, in ascending order, the Tianpeng, Longha, Tangjiaba, and Bocaitian formations. These formations formed the southwestern flank of an anticline, the Zhongzhai-Nanon Anticline near the Fulu Village, and are unconformably overlain by Devonian succession, including the Yujiang and Ping’en formations (Fig. 2D). [Figure 2 is about here] Figure 2. Maps showing the locations of Cambrian exceptionally preserved biotas in Yunnan and Guangxi provinces (A‒C) and the geology of Fulu area, Tianpeng, Funing, southeastern corner of Yunnan (D). The Fulu biota is from the middle part of the Longha Formation. Lithologically, this formation in the Tianpeng-Fulu area consists of carbonate successions with siliciclastic interbeds and is about 2000 meters thick. The formation is divided into three members (Yao et al., 2018). The lower Member exclusively consists of carbonate rocks, dominated in thin to thick-bedded dolomite and interbedded with dolomitic limestone and ribbon limestone. The middle and upper members consist of thin-bedded ribbon limestone, thin-bedded dolomitic limestone, and thin-bedded mudstone, interbedded with middle-thick bedded dolomite, and thin-bedded siltstone. Difference of those two members lies in that the middle Member bears mainly interbeds of dolomite and a few interbeds of mudstone and silty mudstone and the upper Member bears more interbeds of mudstone and silty mudstone but a few interbeds of dolomite. In general, the lithofacies indicate a continuously deepening depositional environment for the Longha Formation. 3. Material and methods All specimens were collected from a 2.5-m-thick interval of dark grey marl in the lower part of the Middle Member of the Longha Formation, which is usually weathered into yellow mudstone. Fossils from the mudstone preserve original profile with a more or less distortion and little compaction. A great number of echinoderms and arthropods are articulated. Most of specimens are photographed with digital camera Nikon D70, and a few of specimens are photographed under a Zeiss stereomicroscope (Model Axio Zoom V16) having a digital head (AxioCamMrM) and a circle light around the lens for providing uniform lighting. Images are processed by the functions of automatic color, contrast, and tonality of Adobe Photoshop CS6 software in order to show, as closely as possible, specimen’s natural color. 4. Fulu Biota The Fulu Biota is dominated by arthropods, of which the polymerid trilobites are abundant and the most diverse group with more than 14 genera. This fossil group is dominated particularly by damesellids (Bergeronites, Palaeadotes, Teinistion, Damesops, Blackwelderia etc., including a possible new damesellid genus) (Fig. 3A‒ E), forming a unique feature in faunal composition for Fulu biota as no damesellids are known from either the older Kaili or the younger Guole biotas. Other polymerids such as Paracoosia, Liostracina (Fig. 3N, O), Monkaspis and three small-sized forms including Torefera (Fig. 3F), an undetermined shumardiid (Fig. 3G) and an undetermined leiostigiid taxon, are common and are also unknown from the Kaili and Guole biotas. Trilobites from the Fulu biota are usually preserved articulated as complete exoskeletons, some of which have the hypostome attached in situ, impressed beneath the glabella (Fig. 3D, E). The complete exoskeleton is recorded for the first time for a number of described polymerid taxa, revealing their thoracic or thoracopygonal features and helping to clarify the concepts of some genera. For instance, Palaeadotes Öpik, 1967 and Bergeronites Sun in Guo, 1965 were considered to be synonymous by Lu and Zhu (1980). The new material of complete exoskeletons of both genera in Fulu biota (Fig. 3A, B) showed they are closely similar but certainly belong to different genera. Bergeronites has more anteriorly placed palpebral lobes and a proportionally smaller pygidium with narrower (tr., exsag.) pleural fields that bear entire pleural or interpleural furrows. In clear contrast, Palaeadotes has posteriorly placed palpebral lobes and a proportionally larger pygidium with broader (tr., exsag.) with pleural fields that bear incomplete pleural or interpleural furrows. In addition, Bergeronites is much smaller than Palaeadotes in size. When fully developed, the mature Palaeadotes reaches to about 90 mm in length but the maximum size of Bergeronites is only about 20 mm long. Cooper et al. (1996) further synonymized Bergeronites and Palaeadotes with Neodrepanura (then called Drepanura). However, Neodrepanura differs from Bergeronites and Palaeadotes greatly as it lacks general spine in cephalon and macropleual spines in thorax (Liu and Lei, 2011), supporting recognizing these are three as separate genera (Zhang and Jell, 1987; Peng et al., 2004). Except for a few new taxa, the polymerid trilobites of Fulu biota are known from formations of either the slope facies in South China or the platform facies in North China, providing new evidence for correlating Guzhangian succession of both regions. Agnostoids

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