The term lagerstätte is used by Palaeontologists to describe a
particularly rich fossil source; a site where fossils are either
exceptionally numerous or exceptionally well preserved (or, ideally,
both). Such lagerstätte are particularly important for our underestanding of the earliest ecosystems which emerged in the Ediacaran and Cambrian periods, which contained many unfamiliar lifeforms, difficult for palaeontologists to understand from fragmentary remains. The Early-to-Middle Cambrian is particularly well represented in such lagerstätte. with examples such as the Chengjiang Biota and the Burgess Shale Fauna having been particularly useful for our understanding of the development of early Metazoan Life. Lagerstätte from the Late Cambrian are, however, much less well known, leaving us with a gap in our understanding of this important period.
In a paper published in the journal Palaeoworld on 19 February 2020, Shan-Chi Peng of the State Key Laboratory of Palaeobiology and Stratigraphy and Nanjing Institute of Geology and Palaeontology of the Chinese Academy of Sciences, Xian-Feng Yang and Yu Liu of the Yunnan Key Laboratory for Palaeobiology and MEC International Joint Laboratory for Palaeobiology and Palaeoenvironment at Yunnan University, Xue-Jian Zhu, also of the State Key Laboratory of Palaeobiology and Stratigraphy and Nanjing Institute
of Geology and Palaeontology of the Chinese Academy of Sciences, Hai-Jing Sun of the National Maritime Museum of China, Samuel Zamora of the Instituto Geológico y Minero de España, and Ying-Yan Mao and Yu-Chen Zhang, again of the State Key Laboratory of Palaeobiology and Stratigraphy of the Chinese Academy of Sciences, report the discovery of an important new fossil Lagerstätte, the Fulu Biota, from the Late Cambrian of Yunnan Province, China.
The Fulu Biota shows exceptional preservation of somei nver-tebrate groups at a critical but poorly known time interval, the Late Cambrian. It is located in the southeastern corner of Yunnan Province at a much younger horizon than the famous Chengjiang and Guanshan biotas, the latter two of which are located in eastern Yunnan and are Early Cambrian in age. Before 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 the basal Miaolingian Series in eastern Guizhou Province and the Guole Biota from the middle Furongian Series in the western Guangxi Autonomous Region, these being about 508 and about 491.5-million-years-old, respectively. As the third exceptionally preserved biota from the upper half of the Cambrian in China, the Fulu Biota from the upper Guzhangian Stage at about 498.5-million-years-old is stratigraphically. close to half way between the older Kaili Biota and the younger Guole Biota, and therefore fills an important gap in our of Cambrian faunas. 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, palaeocontinents, and styles of preservation.
Chart showing global and Chinese chronstratigraphic subdivisions of the Cambrian System, the stratigraphic positions of major Cambrian fossil Lagerstätten (solid stars) and the new Fulu Lagerstätte (open star), and the Agnostoid zonation of the Guzhangian Stage. Abbreviations: Fm, Formation; Sh, Shale; l, Lejopyge laevigata Zone; b, Proagnostus bulbus Zone; r, Linguagnostus reconditus Zone; s, Glyptagnostus stolidotus Zone. Peng et al. (2020).
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 or about 15 km southeast of the Tianpeng Township. From either Fulu or Tianpeng, the Y028 highway leads to the fossil locality.
Maps showing the locations of exceptionally-preserved Cambrian biotas in Yunnan and Guangxi (A), (B) and the geology of the Fulu area, Tianpeng Township, Funing County, and southeastern Yunnan Province (C). Peng et al. (2020).
Cambrian strata are widely exposed in the Tianpeng-Fulu area, which lies at the southeastern corner of Yunnan Province, these exclusively consist of formations belonging to the upper half of the system, i.e., the Miaolingian and Furongian series. No pre-Miaolingian successions are known from this area. The Tianpeng-Fulu area is regarded as one of the classical areas inYunnan for the Cambrian stratigraphic studies, known as the Funing Stratigraphic Subregion of the Southeast Yunnan Startigraphic Region, and holds a number of lithostratigraphic unit stratotypes of formations that include, in ascending order, the Tianpeng, Longha, Tangjiaba, and Bocaitian formations. These formations form the southwestern flank of an anticline, the Zhongzhai-Nanon Anticline near Fulu Village, and are unconformably overlain by Devonian successions, including the Yujiang and Ping’en formations.
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 m thick. The formation is divided into three members. The lower Member exclusively consists of carbonate rocks, dominated by 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. The difference of these two members lies in that the middle Member bears mainly interbeds of dolomite and a few interbeds of mudstone and silty mudstone whereas the upper Member bears more interbeds of mudstone and silty mudstone with a few interbeds of dolomite. In general, the lithofacies indicate a continuously deepening depositional environment for the Longha Formation.
All specimens were collected from a 2.5 m thick interval of dark grey marlin the lower part of the Middle Member of the Longha Formation, which is usually weathered in to yellow mudstone. Fossils from the mudstone preserve original profile with more-or-less no distortion and little compaction. A great number of Echinoderms and Arthropods are articulated.
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), forming a unique feature in the faunal composition for Fulu Biota as no Damesellids are known from either the olde rKaili or the younger Guolebiotas. Other Polymerids such as Paracoosia, Liostracina, Monkaspis and three small-sized forms including Torifera, an undetermined Shumardiid, 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. The complete exoskeleton is recorded for the first time for a number of previously described Polymerid taxa, revealing their thoracic or thoracopygonal features and helping to clarify the concepts of some genera. For instance, Palaeadotes and Bergeronites have been considered to be synonymous since 1980. The new material of complete exoskeletons of both genera in the Fulu Biota shows they are closely similar but certainly belong to different genera. Bergeronites has more anteriorly-placed palpebral lobes and a proportionally smaller pygidium with narrower (transversely, exsagittally) 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 (transversely, exsagittally) 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 may reach about 90 mm in length but the maximum length of Bergeronites is only about 20 mm. A 1996 study further synonymised Bergeronites and Palaeadotes with Neodrepanura (then called Drepanura). However, Neodrepanura differs from Bergeronites and Palaeadotes greatly as it lacks general spines on the cephalon and macropleual spines on the thorax, supporting the position that these are three separate genera.
Polymerid Trilobites and Agnostoid Arthropods from the Fulu Biota, southeastern Yunnan, South China. All in dorsal view; all scale bars are 2 mm. (A) Bergeronites sp., external mould of exoskeleton, NIGP 171327. (B) Palaeadotes hunanensis, early holaspid exoskeleton, NIGP 171328. (C) Damesops sp., exoskeleton, NIGP 171329 (D) Teinistion sp., exoskeleton, NIGP 171330. (E) A new Damesellid genus and species, exoskeleton, NIGP 171331 (F) Torifera sp., exoskeleton, NIGP 171332 (G) A new Shumadiid genus and species, external mould of exoskeleton, NIGP 171333 (H) An Agnostoid exoskeleton assigned tentatively to Agnostus sp., NIGP 171334. (I) Kormagnostus minutus, exoskeleton, NIGP 171335. (J) Clavagnostus spinosus, cephalon, NIGP 171336. (K) Hadragnostus modestus, external mould of exoskeleton, retrodeformation showing inferred strain ellipse, NIGP 171337 (L), (M) Ammagnostus wangcunensis, cephalon and pygidium, NIGP 171338, 171339. (N) Paracoosia asiatica, exoskeleton, NIGP 171340. (O) Liostracina sp., external mould of exoskeleton, NIGP 171341. peng et al. (2020).
Except for a few new taxa, the Polymerid Trilobites of the 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 the Guzhangian succession of both regions.
Agnostoids follow the Polymerid Trilobites indiversity. They include at least six genera, all of which are unknown from either the Kaili or Guole biota. Although Agnostoids are less abundant than Polymerid Trilobites, this fossil group contains some important species such as Hadragnostus (or Formosagnostus) modestus, Kormagnostus minutus, Ammagnostus wangcunensis, Clavagnostus spinosus, and Agnostus sp., all of which, except for Agnostus sp., are known from the Proagnostus bulbus and Linguagnostus reconditus zones in western Hunan. Some of these Agnostoid taxa occur also in Guzhangian formations of Laurentia, Siberia, Australia, Sweden, and Kazakhstan. The Agnostoid assemblage precisely constrains the late Guzhangian age (late Miaolingian Epoch) for the biota. This age indicates that the Fulu Biota is a new exceptionally preserved Cambrian fossil assemblage of South China, occurring above the Kaili Lagerstätte of eastern Guizhou Province (Wuliuan, early Miaolingian) and below the Guole Lagerstätte of western Guangxi (Jiangshanina, middle Furongian). The Fulu Biota differs from theKaili and Guole biotas in having a much more diverse and almost completely different Agnostoid and Polymerid fauna.
Large bivalved and Bradoriid Arthropods are rare in the Fulu Biota, each represented by only a single species. The large bivalved Arthropod is assigned to an undetermined species of Canadaspis and the Bradoriid referred to Anabarochilina australis. The specimen of Canadaspis sp. has suboval-shaped carapace valves with the lowermost part of the left carapace valve slightly damaged so that the right valve is partially exposed. It has a straight hinge in horizontal aspect and the maximum breadth at about mid-length of the hinge. Canadaspis was first known from the Burgess Shale, Canada, and was later reported from the Chengjiang and Kaili biotas, of South China, with a stratigraphic range of lower Nangaoan through middle Wuliuan. The new material of Canadaspis from the Fulu Biota adds a new locality in South China for the species and extends its range into the upper GuzhangianS tage. The Bradoriid Arthropod is characterised by having postplete valves with a highly convex anterior node lying slightly anteroventrally and a less prominent triangular-shaped anterodorsal node. It is confidently assigned as Anabarochilina australis, an intercontinental form known from Gondwana (Australia and India), Laurentia, and Kazakhstan. The genus Anabarochilina is even more widespread, known from Baltica, Avalonia, and Siberia. Previously the known range of Anabarochilina australis has been from the latest Miaolingian Ptychagnostatus gibbus Zone through to the earliest Guzhangian Lejopyge laevigata Zone, the new material of the Fulu Biota extends its geographic distribution to South China and its stratigraphic range up to the lower Linguagnostus reconditus Zone.
Echinoderm, Macroalgae, Brachiopod, Bivalve, large bivalved Arthropod, Bradoriid, Worm, Hyolith, and trace fossils from the Fulu Biota, southeastern Yunnan, South China. All scale bars are 2mm. (A), (E) Cothurnocystid gen. and sp. undetermined, NIGP 171342, 171343 (B) Eocrinoid gen. and sp. undetermined, NIGP 171344 (C) Spinyeocrinoid gen. and sp. undetermined, NIGP 171345. (D) Primitive Mitrocystitid Mitrate, NIGP 171346. (F) Dibrachicystid? gen. and sp. undetermined, NIGP 171347 (G) Doushantuophyton sp., NIGP 171348. (H) Lingulella sp., plan view of pedicle valve external, NIGP 171349 (I) Obolid gen. and sp. undetermined, plan view of dorsal valve external, NIGP 171350.(J) Othriid? gen. and sp. undetermined, plan view of dorsal valve external, NIGP 171351 (K) Canadaspis sp., lateral view, NIGP 171352. (L) Anabarochilina australis, complete carapace in lateral view, NIGP 171353. (M) Palaeoscolecid gen. and sp. undetermined, NIGP 171354 (N) Hyolithid gen. and sp. undetermined, NIGP 171355. (O) Trace fossil, igen. and isp. undetermined, NIGP 171736. Peng et al. (2020).
Echinoderms are rich and diverse in the Fulu Biota, and are dominated by undetermined Eocrinoids and Stylophorans. None of these Echinoderm species are recorded from either the Kaili or Guole Lagerstätten in China or from the Weeks Formation Lagerstätte in Utah, USA, which has a nearly equivalent to, or possibly slightly older age than the Fulu Biota. They likely represent new taxa recorded for the first time from siliciclastic environments of Guzhangian age. Echinoderms of Guzhangian age are very rare worldwide, with a few taxa described from only carbonate faciesin Laurentia (Nevada), Siberia, and Gondwana (Iran). Contrary to other Guzhangian Lagerstätten like the Weeks Formation, in which Echinoderms only represent a small portion of total diversity, Echinoderms are more diverse in the Fulu Biota. The Eocrinoids include a new undetermined form with large marginal spines mounted on thecal plates: and another taxon with a large polyplated theca composed of numerous tiny plates and a holomeric stem. The Stylophorans are dominated by Cothurnocystids and rare Mitrocystitid Mitrates. A possible Dibrachicystid Rhombiferan is also present. The Stylophorans are more or less similar to those from the Furongian formations of Korea and South China (i.e. the Guole Biota). In contrast, the Eocrinoids are very different from those of equivalent Cambrian formations elsewhere.
The Brachiopods of the Fulu Biota appear to consist of three species, among which one belongs to Lingulella, and two others may represent an Obolid and an Orthiid species respectively. Guzhangian Brachiopods from Yunnan and other places in China remain unstudied, except for those from Paibi, Hunan, South China and Wanxian, Hebei, North China. The Fulu Biota bears no shared species with the documented Guzhangian Brachiopods from South and North China. Obollellids in the Fulu Biota are common with about two dozen specimens of dorsal and ventral carapace valves in curren tcollections. This species resembles, in shape and smooth larval shell, Experilingula larga from the Ptychagnostus atavus through Linguagnostus reconditus zones of the Huaqiao Formation, at Paibi, but differs in having thicker, widely spaced concentric lines and in the larger size of the valve (about 10 mm via 3–4.8 mm in width). Six Brachiopod specimens in the current collection are characterised by having a dense ornamentation of radial ridges, and are questionably assigned as undetermined Orthiids because no interior structures of the valves are available for generici dentification.
The 'worms' from the Fulu Biota are moderately rare and are represented by a single Palaeoscolecid species. Material includes three incomplete and four complete specimens with the body 21–29 mm long and 1.5–2.3 mm wide. Palaeoscolecids are also in the Kaili and Guole Biotas, each contains only one species. The species from the Kaili Lagerstätte was described as Palaeoscolex ratcliffi, whereas the species from the Guole Lagerstätte remains unassigned. Hyoliths, trace fossils, and Macroalgae, of the Fulu Biota are very rare, each is represented by only one or two specimens. The Hyolith specimen, characterised by a calcareous conical shell, is an undetermined species probably belonging to Hyolithides. The filled trace fossil on bedding surfaces in burrow is represented by a single, undetermined ichnospecies that is thin in diameter, gentlycurved, and likely branched. The figured specimen of Macroalgae is branched continuously and assigned to Doushantuophyton sp. This genus is widely distributed in the Ediacaran formations of the Yangtze Platform, reported from the Toushantuo (or Doushantuo) Formation of Hubei and Anhui provinces, South China, and in the Vendian formations of the northwestern East European Platform of Russia. It was also recorded from the Kaili Formation, extending its range to the Oryctocephalus indicus Zone of the lower Wuliuan Stage, basal Miaolingian. The discovery of the species in southeastern Yunnan further extends its range to the Linguagnostusre conditus Zone of the Guzhangian Stage, upper Miaolingian.
The moderately diverse Agnostoids in the Fulu Biota are all known from the Huaqiao Formation of northwestern Hunan except for one species assigned tentatively to Agnostus. In northwestern Hunan, these Agnostoids are exclusively Guzhangian in age, among which Hadragnostus modestus ranges from the late Lejopyge laevigata Zone though to the early Linguagnostus reconditus Zone; Ammagnostus wangcunensis and Kormagnostus minutus range from the late Proagnostus bulbus Zone through to the early Linguagnostus reconditus Zone, and the range of Clavagnostus spinosus is restricted to the lower Linguagnostus reconditus Zone. Therefore, their co-ranges suggest the interval bearing the Fulu Biota should be restricted to the lower Linguagnostus reconditus Zone, or at most from the Proagnostus bulbus Zone to the lower Linguagnostusre conditus Zone. This means the Fulu Biota is likely early late Guzhangian in age. Agnostus has never been found in China, the present exoskeleton assignedt entatively to the genus has aprominent preglabellar median furrow, a posteriorly slightly expended postero glabella with centered medial glabella node in the cephalon and a pygidial axis with effaced F1 and F2 furrows and slightly expended postero axis with accurately round end that does not reach to the posterior border furrow. All these features are reminiscent of some specimens assigned to Agnostus pisiformis from Sweden and England, which is associated with Linguagnostus reconditus and is also Guzhangian in age.
The Fulu Biota is characterised by a faunal assemblage with exceptionally preserved organisms belonging to multiple fossil groups. Its discovery opens a new window for the understanding of evolutionary processes of Cambrian life. Together with the Kailiand Guole Biotas, the Fulu Biota forms a successive series of Lagersttäten in the upper half of the Cambrian in South China. All the three biotas are exclusively dominated by Polymerid Trilobites, both in abundance and diversity, but the Fulu Biota is remarkably different in faunal components because it bears a unique assemblage of Damesellid Trilobites with no identical genera and species known from the other two biotas. The first recorded complete or nearly complete exoskeletons of Polymerid Trilobites from the Fulu Lagersttäte help illustrate the entire exoskeletal morphology for a number of incompletely known taxa. The Agnostoids in the Fulu Biota are also unique and more diverse than in the other two. The Fulu Lagersttäte yields rich and diverse Echinoderms that differ from the Guzhangian Echinoderm species from carbonate facies as well as those from the siliciclastic facies of both Kaili and Guole Lagersttäten, and may represent some hitherto unknown species. The discovery of new Echinoderms in such a critical time interval where only little information was available until now improves our understanding of Cambrian faunal composition and fills an important gap between older well known Drumian taxa and the poorly understood Furongian assemblages.
Globally, the Fulu Biota is more or less identical in age with the fauna from the upperWeeks Formation Lagersttäte (Proagnostus bulbus Zone) of Utah, the youngest Cambrian exceptionally-preserved biota of the western USA but seems different in bio-and lithofacies and has different taphonomic features. It is also more or less identical in age with the fauna of the Orsten Lagersttäte (Agnostus pisiforms Zone) from the upper Alum Shale, of southern Sweden, which is clearly different in preservation type and faunal composition. Intensive comparative studies on the Fulu Biota of South China and the Weeks and Orsten faunas are required in order to have a detailed comparison of the Guzhangian faunal and taphonomic features with those biotas occurring on widely separate paleocontinents.
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