Burgess Shale-type Research Articles

Proclivity of nervous system preservation in Cambrian Burgess Shale-type deposits.

Recent investigations on neurological tissues preserved in Cambrian fossils have clarified the phylogenetic affinities and head segmentation in pivotal members of stem-group Euarthropoda. However, palaeoneuroanatomical features are often incomplete or described from single exceptional specimens, raising concerns about the morphological interpretation of fossilized neurological structures and their significance for early euarthropod evolution. Here, we describe the central nervous system (CNS) of the short great-appendage euarthropod Alalcomenaeus based on material from two Cambrian Burgess Shale-type deposits of the American Great Basin, the Pioche Formation (Stage 4) and the Marjum Formation (Drumian). The specimens reveal complementary ventral and lateral views of the CNS, preserved as a dark carbonaceous compression throughout the body. The head features a dorsal brain connected to four stalked ventral eyes, and four pairs of segmental nerves. The first to seventh trunk tergites overlie a ventral nerve cord with seven ganglia, each associated with paired sets of segmental nerve bundles. Posteriorly, the nerve cord features elongate thread-like connectives. The Great Basin fossils strengthen the original description—and broader evolutionary implications—of the CNS in Alalcomenaeus from the early Cambrian (Stage 3) Chengjiang deposit of South China. The spatio-temporal recurrence of fossilized neural tissues in Cambrian Konservat-Lagerstätten across North America (Pioche, Burgess Shale, Marjum) and South China (Chengjiang, Xiaoshiba) indicates that their preservation is consistent with the mechanism of Burgess Shale-type fossilization, without the need to invoke alternative taphonomic pathways or the presence of microbial biofilms.

Waptia-like Euarthropods from Burgess - Shale - type Biotas in the Early Cambrian of Eastern Yunnan, China

Waptia-like euarthropods existed for rather a long time in the Early Cambrian of eastern Yunnan; well preserved representatives come mainly from three Burgess Shale-type biotas: Chengjiang, Xiaoshiba and Guanshan. Here, we introduce a newly-discovered bivalved euarthropod from the Guanshan biota, the specific identity of which cannot be confirmed due to the absence of soft parts and poor preservation of the specimen, but its general morphology allows it be attributed to Waptia. Two representatives from the Chengjiang and Xiaoshiba biotas are also reconsidered: the preservation mode and length of specimens of Clypecaris pteroidea are variable; Clypecaris serrate has limbs beneath the carapace, which can number up to at least 4 pairs. The fossil sections bearing Waptia-like euarthropods occur over a wide area around Dianchi Lake.

The Qingjiang biota-A Burgess Shale-type fossil Lagerstätte from the early Cambrian of South China.

Burgess Shale-type fossil Lagerstätten provide the best evidence for deciphering the biotic patterns and magnitude of the Cambrian explosion. Here, we report a Lagerstätte from South China, the Qingjiang biota (~518 million years old), which is dominated by soft-bodied taxa from a distal shelf setting. The Qingjiang biota is distinguished by pristine carbonaceous preservation of labile organic features, a very high proportion of new taxa (~53%), and preliminary taxonomic diversity that suggests it could rival the Chengjiang and Burgess Shale biotas. Defining aspects of the Qingjiang biota include a high abundance of cnidarians, including both medusoid and polypoid forms; new taxa resembling extant kinorhynchs; and abundant larval or juvenile forms. This distinctive composition holds promise for providing insights into the evolution of Cambrian ecosystems across environmental gradients.

Extensive bioturbation in a middle Cambrian Burgess Shale–type fossil Lagerstätte in northwestern Canada

Extensive bioturbation in a middle Cambrian Burgess Shale–type fossil Lagerstätte in northwestern Canada

First report on Guanshan Biota (Cambrian Stage 4) at the stratotype area of Wulongqing Formation in Malong County, Eastern Yunnan, China

Exceptionally preserved fossils, such as those from Cambrian Burgess Shale-type fossil-Lagerstätten are critical because of their unique contributions to knowledge of the phylogenetic radiation and palaeoecological expansion of metazoans during the Cambrian explosion. Critically, these deposits provide information that is usually unobtainable from shelly and skeletonized fossils alone. The Guanshan Biota (Cambrian Series 2, Stage 4) in the Yunnan Province of South China, has produced abundant and diverse, exquisitely preserved fossils that often retain soft tissues and organs. To date, most fossils from the Guanshan Biota have been collected from localities such as Gaoloufang and Gangtoucun, which have become inaccessible due to new urban expansions and constructions of residential buildings. Here we present the first report of soft bodied fossils from a new section at Kanfuqing, close to the Wulongqing village in Malong County, approximately 3 km east of the Wulongqing Formation stratotype section. Fossils retain soft morphology, and include brachiopods with delicate marginal setae, priapulids with well-preserved sclerites and vetulicolians with entire sections of body. In addition, this fauna includes rare occurrences of trilobites preserved with soft tissues replicated as pyrite pseudomorphs after weathering. This discovery represents an important palaeogeographical extension of soft-bodied fossils of the Guanshan fauna to the east of the Xiaojiang Fault (related to Tsinning tectonic movements ca. 700 Ma). The fauna from the new Kanfuqing section is similar to that reported from the Wulongqing Formation west of the Xiaojiang Fault, and thus has significant implications for early Cambrian palaeogeography, faunal successions and palaeoenvironments of eastern Yunnan.

The Kinzers Formation (Pennsylvania, USA): the most diverse assemblage of Cambrian Stage 4 radiodonts

AbstractRadiodonta, apex Cambrian predators such asAnomalocarishave been known from the Kinzers Formation (Cambrian Series 2, Stage 4 – Pennsylvania, USA) for nearly 100 years. Work over the last ten years, mainly on radiodont material from the Chengjiang (Cambrian Series 2, Stage 3 – Yunnan, China) and Burgess Shale (Miaolingian, Wuliuan – British Columbia, Canada), has greatly improved our knowledge of the diversity and disparity of radiodonts and their frontal appendages, including the description of new species, genera and families. Previous work identified two species of radiodonts from the Kinzers Formation:Anomalocaris pennsylvanicaResser, 1929 andAnomalocaris? cf.pennsylvanicabased on isolated frontal appendage material (Briggs, 1979). A restudy of Kinzers Formation material shows that only some of the specimens can be confirmed asAnomalocaris pennsylvanica, and a number of specimens previously attributed toAnomalocarisin fact belong to other more recently discovered radiodont generaAmplectobeluaandTamisiocaris. This reinterpretation makes the Kinzers Formation the most diverse Cambrian Stage 4 Burgess Shale Type Lagerstätten in terms of number of radiodont species. This assemblage includes the youngest knownTamisiocarisand the first from outside Greenland, the onlyAmplectobeluafrom Stage 4 and the oldest from Laurentia, two specimens tentatively assigned to the recently described Chengjiang genusLaminacaris, and the endemicAnomalocaris pennsylvanica. The identification of these new radiodont taxa increases the total known diversity of the Kinzers Formation to more than ten species, and so it should now be considered a Tier 2 Lagerstätte.

On the edge of exceptional preservation: insights into the role of redox state in Burgess Shale-type taphonomic windows from the Mural Formation, Alberta, Canada

Animals originated in the Neoproterozoic and 'exploded' into the fossil record in the Cambrian. The Cambrian also represents a high point in the animal fossil record for the preservation of soft tissues that are normally degraded. Specifically, fossils from Burgess Shale-type (BST) preservational windows give paleontologists an unparalleled view into early animal evolution. Why this time interval hosts such exceptional preservation, and why this preservational window declines in the early Paleozoic, have been long-standing questions. Anoxic conditions have been hypothesized to play a role in BST preservation, but recent geochemical investigations of these deposits have reached contradictory results with respect to the redox state of overlying bottom waters. Here, we report a multi-proxy geochemical study of the Lower Cambrian Mural Formation, Alberta, Canada. At the type section, the Mural Formation preserves rare recalcitrant organic tissues in shales that were deposited near storm wave base (a Tier 3 deposit; the worst level of soft-tissue preservation). The geochemical signature of this section shows little to no evidence of anoxic conditions, in contrast with published multi-proxy studies of more celebrated Tier 1 and 2 deposits. These data help confirm that 'decay-limited' BST biotas were deposited in more oxygenated conditions, and support a role for anoxic conditions in BST preservation. Finally, we discuss the role of iron reduction in BST preservation, including the formation of iron-rich clays and inducement of sealing seafloor carbonate cements. As oceans and sediment columns became more oxygenated and more sulfidic through the early Paleozoic, these geochemical changes may have helped close the BST taphonomic window.

Characterization of kerogenous films and taphonomic modes of the Sirius Passet Lagerstätte, Greenland

The Sirius Passet Lagerstatte (northern Greenland) is an exceptionally well-preserved early Cambrian faunal community containing a diverse array of stem-group euarthropods, lobopodians, worms, sponges, and the iconic Halkieria. Material collected in situ during recent expeditions has yielded a range of fossil specimens that are preserved as two-dimensional, reflective films. Here we document in detail, for the first time from the Sirius Passet, compressed, kerogenous fossil films characteristic of Burgess Shale–type (BST) preservation. The carbon structure and the taphonomic mode associated with these films were investigated using Raman spectroscopy. Our analysis confirms that these reflective films are kerogenous, showing a higher D1 (disordered) band and G (graphite) band intensity and area, indicating a greater concentration of disordered carbon compared to the surrounding matrix. The spectral characteristics of the fossils denote moderately ordered kerogenous matter, indicating that the transitional Buen Formation that hosts the Sirius Passet was thermally altered at a peak temperature of 409 ± 50 °C. Phyllosilicate minerals are associated with the films, but they are not anatomical or taxon-specific, suggesting that the higher thermal maturation of the kerogen in the Sirius Passet produced a uniform distribution of minerals. This is unlike the kerogenous films in the Burgess Shale Lagerstatte (British Columbia, Canada) that have been metamorphosed at a lower temperature of 335 ± 50 °C and typically show an anatomically specific phyllosilicate distribution. Preservation as kerogenous films, however, is not continuous, and the presence of other taphonomic modes not indicative of BST preservation suggests that the Sirius Passet represents a unique and complex deposit.

A mineralogical signature for Burgess Shale–type fossilization

A mineralogical signature for Burgess Shale–type fossilization

Ichnotaxonomy of the Cambrian Spence Shale Member of the Langston formation, Wellsville Mountains, Northern Utah, USA

The Spence Shale of northern Utah is the oldest North American middle Cambrian (∼506–505 Ma) Burgess Shale-type (BST) deposit and, unlike previously thought for BST deposits, has a very diverse ichnofauna. Twenty-four ichnogenera and 35 ichnospecies were identified: Archaeonassa (A. fossulata and A. jamisoni isp. nov.), Arenicolites carbonaria, Aulichnites, Bergaueria (B. hemispherica and B. aff. perata), Conichnus conicus, Cruziana (C. barbata and C. problematica), Dimorphichnus, Diplichnites (D. cf. binatus, D. gouldi, and D. cf. govenderi), Gordia marnia, Gyrophyllites kwassizensis, Halopoa aff. imbricata, Lockeia siliquaria, Monomorphichnus (M. bilinearis, M. lineatus, and M. cf. multilineatus), Nereites cf. macleayi, Phycodes curvipalmatum, Phycosiphon incertum, Planolites (P. annularius, P. beverleyensis, and P. montanus), Protovirgularia (P. dichotoma and P. cf. pennatus), Rusophycus (R. carbonarius, R. cf. pudicus, and R. cf. cerecedensis), Sagittichnus lincki, Scolicia, Taenidium cf. satanassi, Teichichnus cf. nodosus, and Treptichnus (T. bifurcus, T. pedum, and T. vagans). The ichnofossils comprise three ichnocoenoses—Rusophycus-Cruziana, Sagittichnus, and Arenicolites-Conichnus—representing dwelling, deposit- and filter-feeding, grazing, locomotion, and predation behaviors of organisms (e.g., annelid worms and trilobites). Two ichnofossil associations are suggestive of predation: (1) Planolites terminating at a Rusophycus; and (2) Archaeonassa crosscutting a Taenidium. The Spence Shale ichnofauna represent a distal Cruziana Ichnofacies and depauperate, distal Skolithos Ichnofacies. A new ichnospecies of Archaeonassa is proposed, A. jamisoni isp. nov., and Ptychoplasma (Protovirgularia) vagans is herein transferred to Treptichnus. This study is the first ichnotaxonomic study of the Spence Shale and North American BST deposits and shows highly diverse ichnofaunas can be present in BST deposits.

Comparisons between Cambrian Lagerstätten assemblages using multivariate, parsimony and Bayesian methods

Exceptional fossil deposits exhibiting soft-part preservation, or Konservat-Lagerstätten, are prevalent in Cambrian rocks and provide detailed information on fossil assemblages not available from conventional deposits. It has long been recognised that many of these assemblages exhibit certain taxonomic similarities, with many elements seemingly having cosmopolitan distributions. These types of assemblages, particularly those of Cambrian age, have become known as Burgess Shale-type (BST) biotas, named for the famous deposit in the Canadian Rocky Mountains where fossils preserved in this way were first discovered. This study provides the first broad-scale analysis of the assemblage relationships between all major BST biotas. We compiled a database of the presences and absences of over 600 genera within 12 Lagerstätten from Laurentia, Siberia, South China and East Gondwana, ranging in age from Cambrian Series 2 through Series 3 (late-early to middle Cambrian; c. 518–502Ma), and analysed this using a variety of quantitative methods in order to investigate the relationships between these sites. Non-metric multidimensional scaling (NMDS) ordination, cluster analysis and Parsimony Analysis of Endemicity (PAE) were used to group localities and examine relationships. We also used Bayesian inference and illustrate the benefits of this approach to biogeographic studies. Results suggest that both space and time have important effects on the taxonomic constitution of BST biotas, and that the similarity of these assemblages appears to increase from Series 2 through Series 3, largely driven by increases in cosmopolitanism of biomineralised taxa such as trilobites and brachiopods. There is also evidence of higher-level taxonomic turnover across this period. Endemic taxa help amplify these patterns, despite their frequent exclusion from biogeographic analyses.

New paleoscolecid worms from the early Cambrian north margin of the Yangtze Platform, South China

AbstractThe Cambrian Yanwangbian assemblage (Series 2, Stage 4) in South Shaanxi, China, is one of the Burgess Shale–type faunas as it represents the only relatively diverse Cambrian biota from the north margin of the Yangzte Platform, South China. The paleoscolecids (Cycloneuralia) illustrated herein are one of the major components of the fauna, although they appear to be much less abundant than skeletonized fossils, according to available collections. A new taxon,Shaanxiscolex xixiangensisnew genus new species, is described based on the scleritome pattern: each annulus has two rows of alternatingHadimopanella-type plates positioned close to the borders, and a mosaic pattern of microplates occurs between the plates and within intersegmental furrows. The occurrence of the new taxon confirms a fairly diversified and widespread distribution of paleoscolecidan worms recognized in the early Cambrian of South China. Moreover, the ecology of paleoscolecids is reappraised based on burial position of theS. xixiangensisand gut contens of Cambrian taxa from South China, hinting that paleoscolecids (at least some taxa) were both deposit feeders and carnivores, as well as active bioturbators in the substrates of the Cambrian sea, which sheds new light on the ‘Cambrian Substrate Revolution.’

Fentou Biota: A Llandovery (Silurian) Shallow-Water Exceptionally Preserved Biota from Wuhan, Central China

An exceptionally preserved biota is described from the middle Telychian (Llandovery, Silurian) Fentou Formation of Wuhan, Central China, which preserves nontrilobite arthropods, cnidarians, echinoderms, sponges, fish, and algae as well as abundant shelly fossils and trace fossils in the Skolithos-Cruziana ichnofacies. This biota can be divided into two assemblages on the basis of the biological characteristics, fossil-bearing strata, and their sedimentary environments. Assemblage 1 comprises nonbiomineralized phyllocarids, Sphenothallus, conulariids, complete crinoids and stelleroids, and Burgess Shale–type sponges as well as some uncertain fossils in taxonomy and abundant marine shelly fossils. Assemblage 2 consists of numerous eurypterids, agnathans, chondrichthyes, and a few conulariids, algae, as well as shelly euryhaline fossils. Discoveries of the Fentou biota expand the temporospatial distribution and sedimentary environment of the exceptionally preserved Silurian biota and advances a deeper understanding of the biological assemblage and ecological system in the Llandovery. It also provides new data for studying the biological recovery and radiation under the background of the littoral sea (assemblage 1) and estuary-delta (assemblage 2) environments after the latest Ordovician mass extinction.

Palaeoredox geochemistry and bioturbation levels of the exceptionally preserved early Cambrian Indian Springs biota, Nevada, USA

The early Cambrian Indian Springs biota of western Nevada, USA, exhibits Burgess Shale-type (BST) preservation of a diverse array of animal phyla, including the earliest definitive echinoderms. It therefore provides an important window on animal life during the Cambrian radiation. The objective of this study was to analyse the trace metal palaeoredox geochemistry and bioturbation levels of this BST deposit in order to characterize the palaeoenvironmental conditions in which these animals lived and their remains preserved. A total of 28 rock samples were collected from outcrops at three previously reported intervals of exceptional preservation at the Indian Springs locality, as well as from one interval not exhibiting such preservation. An additional 20 random samples were collected from talus for comparison. In the laboratory, the samples were analysed for trace metal palaeoredox indices (V/Cr and V/(V + Ni) ratios). Bioturbation levels were assessed through X-radiography and petrographic thin sections using the ichnofabric index (ii) method. Additional samples from coeval strata of the Poleta Formation in the White-Inyo Mountains, CA, that lack BST preservation were also analysed with the same methodology. Results indicate that oxic bottom water conditions dominated during deposition of these strata, despite consistently low bioturbation levels. This pattern holds for intervals with BST preservation and those without. Although ephemeral incursions of low-oxygen waters may have taken place, there is no evidence for persistent oxygen restriction in these palaeoenvironments. The low levels of bioturbation indicate limited mixed layer development and a redox boundary near the sediment–water interface, likely allowing post-burial BST preservation to occur even in this setting dominated by oxic bottom waters. Palaeoecological reconstructions and taphonomic hypotheses relating to the Indian Springs Lagerstatte must consider the palaeoredox conditions revealed in this study. With the dispensing of anoxic bottom waters as a requirement for BST preservation, other models proposing a role for clay minerals, the presence of hypersaline brines and the actions of Fe-reducing bacteria as mechanisms for exceptional preservation warrant renewed consideration.

A new Burgess Shale-type deposit from the Ediacaran of western Mongolia.

Preservation of soft-bodied organisms is exceedingly rare in the fossil record. One way that such fossils are preserved is as carbonaceous compressions in fined-grained marine sedimentary rocks. These deposits of exceptional preservation are known as Burgess Shale-type (BST) deposits. During the Cambrian Period, BST deposits are more common and provide a crucial view of early animal evolution. The earliest definitive fossil evidence for macroscopic animal-grade organisms is found in the preceding Ediacaran Period. BST deposits from the Ediacaran are rarer and lack conclusive evidence for animals. Here we report the discovery of a new Ediacaran BST deposit with exceptional preservation of non-mineralizing macro-organisms in thinly bedded black shale from Zavkhan Province, western Mongolia. This fossil assemblage, here named the Zuun-Arts biota, currently consists of two new species of probable macroscopic multicellular benthic algae. One species, Chinggiskhaania bifurcata n. gen., n. sp., dominates the biota. The other species, Zuunartsphyton delicatum n. gen., n. sp., is known from three specimens. SEM-EDS analysis shows that the fossils are composed of aluminosilicate clay minerals and some carbon, a composition comparable to fossils from the Cambrian Burgess Shale biota. This discovery opens a new window through which to view late Precambrian life.

Unusual Deep Water sponge assemblage in South China-Witness of the end-Ordovician mass extinction.

There are few sponges known from the end-Ordovician to early-Silurian strata all over the world, and no records of sponge fossils have been found yet in China during this interval. Here we report a unique sponge assemblage spanning the interval of the end-Ordovician mass extinction from the Kaochiapien Formation (Upper Ordovician-Lower Silurian) in South China. This assemblage contains a variety of well-preserved siliceous sponges, including both Burgess Shale-type and modern type taxa. It is clear that this assemblage developed in deep water, low energy ecosystem with less competitors and more vacant niches. Its explosion may be related to the euxinic and anoxic condition as well as the noticeable transgression during the end-Ordovician mass extinction. The excellent preservation of this assemblage is probably due to the rapid burial by mud turbidites. This unusual sponge assemblage provides a link between the Burgess Shale-type deep water sponges and the modern forms. It gives an excellent insight into the deep sea palaeoecology and the macroevolution of Phanerozoic sponges, and opens a new window to investigate the marine ecosystem before and after the end-Ordovician mass extinction. It also offers potential to search for exceptional fossil biota across the Ordovician-Silurian boundary interval in China.

High-resolution geochemical evidence for oxic bottom waters in three Cambrian Burgess Shale-type deposits

The Cambrian radiation of complex animals is a fundamental event in the history of life on Earth. Much of our understanding of this event is made possible through the study of exceptionally preserved fossils in Burgess Shale-type (BST) deposits. Based on bioturbation levels in BST deposits, they are often interpreted as representing restricted oxygen settings. This study tests the low-oxygen interpretation through analysis of geochemical paleoredox proxies and bioturbation levels in three BST deposits: the early Cambrian Maotianshan Shale (China), the middle Cambrian Wheeler Shale (USA), and the middle Cambrian Spence Shale (USA). Results from 96 samples show fine-scale geochemical evidence for oxic bottom water conditions during the deposition of these three BST deposits. Trace element paleoredox indices (PI) give consistent oxic signals in all three shales. In addition, total organic carbon (TOC) and total sulfur (TS) levels in the Spence Shale are extremely low. The average C/S ratio is 3.1, comparable to values for modern oxic marine water. Bioturbation levels in all three shales are low, with rare development of minimal to moderate horizontal bioturbation. While short-term oxygen fluctuations, or poikiloaerobic conditions, could still have sporadically existed in these settings, this study shows that these BST deposits were deposited in a dominantly oxic paleoredox setting. Evidence for low bioturbation levels coupled with paleoredox geochemistry indicative of oxic bottom waters suggests that pervasive exaerobic conditions, with an oxic water column positioned above oxygen-depleted sediment pore waters, may have existed in many Cambrian BST deposit paleoenvironments.

A late surviving xenopod (Arthropoda) from the Ordovican Period, Wales

AbstractThe Middle Ordovician Llanfallteg Formation has yielded remains of soft-bodied organisms previously known only from Cambrian Burgess Shale-type deposits. A new arthropod Etania howellsorum gen. et sp. nov. is described here, characterized by a semi-circular cephalon, clusters of spinose endites on the endopod and exopods with ovoid distal lobes. These characters are consistent with xenopod affinities, a clade otherwise known exclusively from the Cambrian Period. The discovery of E. howellsorum demonstrates that a number of Burgess Shale-type taxa, including xenopods, survived past the Cambrian Period (albeit within a restricted environment) and may have been outcompeted during the Great Ordovician Biodiversification Event (GOBE).

New records of Burgess Shale-type taxa from the middle Cambrian of Utah

AbstractCambrian strata of the Laurentian craton contain numerous examples of Burgess Shale–type faunas. Although displaying a more or less concentric distribution around the cratonal margin, most faunal occurrences are in present-day western North America, extending from the Northwest Territories to California. Nevertheless, the soft-bodied and lightly skeletalized fossils in most of these Lagerstätten are highly sporadic. Here, we extend knowledge of such Middle Cambrian occurrences in Utah with reports of four taxa. An arthropod from the Marjum Formation,Dytikosicula desmataegen. et sp. nov., is a putative megacheiran. It is most similar toDicranocaris guntherorum, best known from the younger Wheeler Formation, but differs primarily in the arrangement of pleurae and overall size. Along with a specimen of ?Yohoiasp, a new species ofYohoia,Y. utahanasp. nov., is described. It differs from the type and only known species,Y. tenuis, principally in its larger size and shorter exopods; it is the first description of this genus from outside the Burgess Shale. A new species of a stem-group lophotrochozoan from the Spence Shale,Wiwaxia herkasp. nov., possesses a palisade of dorso-lateral spines that are more robust and numerous than the type species ofWiwaxia,W. corrugata. Another notable taxon isEldonia ludwigifrom the Marjum Formation, which is interpreted as a primitive ambulacrarian (assigned to the cambroernids) and a new specimen of the ?cnidarianCambrorhytiumfrom the Wheeler Shale is illustrated.

An Ordovician variation on Burgess Shale-type biotas.

The Cambrian Burgess Shale-type biotas form a globally consistent ecosystem, usually dominated by arthropods. Elements of these communities continued into the Early Ordovician at high latitude, but our understanding of ecological changes during the Great Ordovician Biodiversification Event (GOBE) is currently limited by the paucity of Ordovician exceptionally preserved open-marine faunas. Here we clarify the early stages of the GOBE by describing a new open-marine Konservat-Lagerstätte from the Early Ordovician of Wales. The Afon Gam Biota includes many lineages typical of the Cambrian Burgess Shale-type biotas, but the most abundant groups were sponges, algae and worms, with non-trilobite arthropods being unexpectedly rare. Labile tissues occur abundantly in the sponges and are also present in other groups, including brachiopods and hyoliths. Taphonomic biases are considered and rejected as explanations for arthropod rarity; the preserved biota is considered to be an approximation to the original community composition. We note that other exceptionally preserved communities in the Welsh Ordovician are also sponge-dominated, suggesting a regional change in benthic ecology during the early stages of the GOBE.