Burgess Shale-type Research Articles

Highly resolved taphonomic variations within the Early Ordovician Fezouata Biota

The Fezouata Biota (Morocco) is a Burgess Shale-type (BST) assemblage that provides a wealth of information on Early Ordovician ecosystems. Much work has been done to compare the preservation of the Fezouata Biota to other BSTs. However, studies investigating preservation variations within the Fezouata Biota are rare. Here, we use probabilities to investigate the preservation of various ecological categories of Fezouata eumetazoans. Complex taphonomic processes and phylum-specific constraints have led to the better preservation of predators/scavengers in this biota. However, no differences in preservation are observed between vagile and sessile taxa. Importantly, Tremadocian taxa are better preserved than Floian ones. As such, this study highlights the gradual closure of the BST window of preservation in the Zagora region of Morocco and constitutes a benchmark for future palaeoecological and evolutionary studies on the Fezouata Biota.

Thermal History of Cambrian Burgess Shale-Type Deposits: New Insights from the Early Cambrian Chengjiang and Qingjiang Fossils of South China

Thermal History of Cambrian Burgess Shale-Type Deposits: New Insights from the Early Cambrian Chengjiang and Qingjiang Fossils of South China

Unveiling an ignored taphonomic window in the early Cambrian Chengjiang Biota

Abstract The exceptionally preserved soft-bodied fossils from the Chengjiang Biota of southwest China have proved to be critical for our understanding of the biodiversity and ecology of the Cambrian explosion of animals. Almost all previously reported soft-bodied Chengjiang fossils are from the event mudstone beds (EB) of the Yu’anshan Formation. Here, we present the first comprehensive investigation of the soft-bodied fossils from the interbedded background mudstone beds (BGB), based on collections made across the past decade, and characterize their preservation. Soft internal cellular organs/tissues, such as digestive tracts and glands, cardiovascular systems, nervous systems, and musculature, are predominantly preserved as carbonaceous compressions, in contrast to their iron oxide–rich preservation in the EB. Our work highlights two distinct preservation modes within a single Burgess Shale–type Lagerstätte, possibly due to the complex interplay of decay, kerogenization, and pyritization.

Trilobites of the Cranbrook Lagerstätte (Eager Formation, Cambrian Stage 4), British Columbia

Abstract The Eager Formation (Cambrian Stage 4) of the Cranbrook area, British Columbia, contains abundant, sometimes beautifully preserved, trilobites and rare non-biomineralized taxa. Trilobites were first reported just over a century ago but have received little research attention, resulting in uncertainty in the number and identity of species within the assemblage and ambiguity in the age of the fauna. The trilobites of the Eager Formation in the Cranbrook area are described herein based largely upon material collected in 2015. A minimum of eight (and perhaps up to 11) trilobite species are recognized. The four species of olenelloids (Olenellus santuccii Webster n. sp., Olenellus? schofieldi, Mesonacis eagerensis, and Wanneria cranbrookense Webster n. sp.) are by far the most abundant elements of the fauna. At least two, and perhaps as many as five, species of dorypygid are present, as are two species of “ptychoparioids”. Paucity and poor preservational quality of specimens mean that the various dorypygid and “ptychoparioid” species are left in open nomenclature. Trilobite diversity in the Cranbrook Lagerstätte is comparable to that within other Lagerstätten from Cambrian Stage 4 (Series 2) of Laurentia. The diversity and abundance of trilobites, combined with biostratinomic and trace fossil data, suggest that the assemblage is autochthonous and/or parautochthonous, and that the local environment was at least periodically able to support a “typical” benthic trilobite community. The age of the Cranbrook Lagerstätte is constrained to lie within the middle Dyeran Stage of Laurentia, within what was a substantial stratigraphic gap in the distribution of Burgess Shale-type Lagerstätten. UUID: http://zoobank.org/5beab9df-6b6a-4d6d-95e8-57057cd47a66

Life in the Cambrian shallows: Exceptionally preserved arthropod and mollusk microfossils from the early Cambrian of Sweden

Abstract Burgess Shale–type (BST) Lagerstätten record an exceptional variety of Cambrian soft-bodied fauna, yet these deposits are typically restricted to outboard depositional settings >1000 km from the paleocoastline. For shallow, well-oxygenated shelf environments, our knowledge of non-mineralized animals (the majority of diversity) is severely limited, giving rise to substantial bias in our perception of Cambrian biotas. An alternate means of detecting soft-bodied Cambrian fauna, independent of paleobathymetry, is to use acid maceration to extract microscopic organic remains of non-mineralized animals, known as “small carbonaceous fossils” (SCFs). Here, a hitherto unknown diversity of Cambrian arthropod and mollusk remains are reported from shallow-marine sediments (Cambrian Stage 3 Mickwitzia Sandstone, Sweden). These microfossils comprise a variety of arthropod cuticles preserving sub-micron-scale anatomy alongside abundant radular mouthparts from mollusks—among the oldest known arthropod and molluscan SCFs on record. Significantly, at least three distinct types of fossil radula are identifiable (uniseriate, distichous, and polystichous forms), revealing that substantial diversification of the basic molluscan radula had already taken place by the early Cambrian. These cryptic elements of the biota—otherwise undetectable in such deposits—offer novel insights into Cambrian primary consumers as well as aspects of the fauna that are absent from deeper-water BST deposits.

Ontogeny and brooding strategy of the early Cambrian arthropod Isoxys minor from the Qingjiang biota

†Isoxys is a worldwide distributed bivalved arthropod known almost exclusively from Cambrian Burgess Shale-type Lagerstätten. Outline analyses using 34 specimens of the iconic large bivalved arthropod †Isoxys minor from the Cambrian Stage 3 (~518 Ma) Qingjiang biota and the Cambrian Stage 4 Guanshan biota, interpret that they are the same species and there is a very slight difference in the shape of the outlines of the carapaces between the two biotas. This suggests that environment might be driving intraspecific variation. Quantitative analysis of shape changes during growth using 51 specimens of †I. minor from the Qingjiang biota, reveals that its valves gradually elongate and the ratio of cardinal spines and spherical eyes relative to the valve length significantly decreases during postembryonic development. †I. minor has proportionally large cardinal spines and eyes in the earliest stages, and this allometric growth is beneficial for self-protection and foraging, which may have improved the survival rate of individuals with these characters. In addition, two of the specimens document the evidence of brood care in †I. minor, and the egg cluster occupies almost the entire dorsal region under the carapace. Compared to other early Paleozoic egg-carrying arthropods, †I. minor broods have the highest number (~300 per clutch) of small (Ø, ~0.5 mm) eggs. Since the ovigerous individuals are almost half the size of the adults, †I. minor may have possessed reproductive ability during the early life stage. The results indicate that spines played an antipredatory role for †I. minor, and that it followed an r-strategy of reproducing with many individuals at an early stage. †I. minor also represents the earliest diverging arthropod from which brood care has been documented.

First record of growth patterns in a Cambrian annelid.

Early annelid evolution is mostly known from 13 described species from Cambrian Burgess Shale-type Lagerstätten. We introduce a new exceptionally well-preserved polychaete, Ursactis comosa gen. et sp. nov., from the Burgess Shale (Wuliuan Stage). This small species (3-15 mm) is the most abundant Cambrian polychaete known to date. Most specimens come from Tokumm Creek, a new Burgess Shale locality in northern Kootenay National Park, British Columbia, Canada. Ursactis has a pair of large palps, thin peristomial neurochaetae and biramous parapodia bearing similarly sized capillary neurochaetae and notochaetae, except for segments six to nine, which also have longer notochaetae. The number of segments in this polychaete range between 8 and 10 with larger individuals having 10 segments. This number of segments in Ursactis is remarkably small compared with other polychaetes, including modern forms. Specimens with 10 segments show significant size variations, and the length of each segment increases with the body length, indicating that body growth was primarily achieved by increasing the size of existing segments rather than adding new ones. This contrasts with most modern polychaetes, which typically have a larger number of segments through additions of segments throughout life. The inferred growth pattern in Ursactis suggests that annelids had evolved control over segment addition by the mid-Cambrian.

The Cambrian cirratuliform Iotuba denotes an early annelid radiation.

The principal animal lineages (phyla) diverged in the Cambrian, but most diversity at lower taxonomic ranks arose more gradually over the subsequent 500 Myr. Annelid worms seem to exemplify this pattern, based on molecular analyses and the fossil record: Cambrian Burgess Shale-type deposits host a single, early-diverging crown-group annelid alongside a morphologically and taxonomically conservative stem group; the polychaete sub-classes diverge in the Ordovician; and many orders and families are first documented in Carboniferous Lagerstätten. Fifteen new fossils of the 'phoronid' Iotuba (=Eophoronis) chengjiangensis from the early Cambrian Chengjiang Lagerstätte challenge this picture. A chaetal cephalic cage surrounds a retractile head with branchial plates, affiliating Iotuba with the derived polychaete families 'Flabelligeridae' and Acrocirridae. Unless this similarity represents profound convergent evolution, this relationship would pull back the origin of the nested crown groups of Cirratuliformia, Sedentaria and Pleistoannelida by tens of millions of years-indicating a dramatic unseen origin of modern annelid diversity in the heat of the Cambrian 'explosion'.

Aluminium-normalised trace-element paleoredox proxies and their application to the study of the conditions of Burgess Shale-type preservation

The paleo-ecological settings of Burgess Shale-type (BST) fossils have been the subject of extensive investigations, particularly with regard to the role of anoxia in their exceptional preservation. Our understanding of the complexity of both paleontological and geochemical environmental proxies has evolved with increased knowledge of niche communities and marine geochemical and biogeochemical processes. Accordingly, dated approaches should be reevaluated. The commonly applied paleoredox proxies V/Cr, Ni/Co, and V/(V + Ni), as well as the redox proxy V/Al2O3 and productivity proxy Ba/Al2O3, were all tested on the Wheeler Formation (Utah, USA) for which a fluctuating oxycline environment has been well established based on paleontological features. Subsequently, these proxies were applied to three additional BST fossil-bearing deposits: the Emigsville Member of the Kinzers Formation (Pennsylvania, USA), the Burgess Shale (British Columbia, CA) and the Emu Bay Shale (South Australia, AU). Their host shales lack perceptible V of marine origin, indicative of oxic conditions, in contrast to the Wheeler and brine-related strata from the Burgess Shale which include additional marine input of V in some beds, consistent with varying redox conditions. The black shales of the Longs Park Member (Kinzers) have elevated V/Al2O3 indicative of anoxic conditions. Molybdenum concentrations are relatively low in most samples, but minor variations tend to correlate with V/Al2O3 patterns. Ba/Al2O3 indicates high productivity with deposition of BST fossils in the Wheeler Formation, and diagenetic remobilisation of Ba owing to sediment anoxia in the Burgess Shale. Our findings show that redox proxy V/Al2O3 can be effectively applied to BST samples, whereas Ba/Al is a reliable proxy for low to moderate paleoproductivity levels and may be useful as a secondary or tangential proxy for redox conditions. Taphonomic processes leading to BST preservation occur in a variety of environments characterised by oxyclines, matgrounds, variable sedimentation rates, hypersalinity and/or anoxia. KEY POINTS V/Al2O3 and Ba/Al2O3 are effective proxies for anoxia and productivity in BST deposits. BST preservation can occur in a variety of depositional environments. Marine anoxia is not required for BST preservation.

New Material of Carbonaceous Compressions from the ∼1.5 Ga Singhora Group, Chhattisgarh Supergroup, India, and their Interpretation as Benthic Algae

The origin, antiquity, and affinity of benthic seaweeds (multicellular algae) in the geological past are shrouded in mystery due to their preservation bias. In this study, we present a new material of well-preserved carbonaceous compression fossils in shale horizons of the Mesoproterozoic (ca. ∼1,500–1,300 Ma) Singhora Group of the Chhattisgarh Supergroup. Eleven distinct taxa, including one new taxon, Palaeoscytosiphon shuklaii, n. gen. et. sp., and one new species, Jiuqunaoella sergeevii, n. sp., are established. Four unidentified morphologies are also reported. Morphologically, the carbonaceous fossils are fan-shaped, palmate, elongated, leaf-like algal thalli with/without holdfast at the base, isolated or dichotomously branched long filaments, along with multicellular reproductive structures. The results of laser Raman spectroscopy and energy dispersive X-ray spectroscopy (EDX) are also presented in support of their biogenicity. Collectively, the preservation mode of the Singhora carbonaceous fossils suggests multicellular algal affinity and adds to a Burgess Shale-type (BST) taphonomic window in the Pre-Ediacaran biosphere.

Preservation and diagenesis of soft-bodied fossils and the occurrence of phosphate-associated rare earth elements in the Cambrian (Wuliuan) Spence Shale Lagerstätte

The Spence Shale Lagerstätte is a middle Cambrian (Miaolingian Series; Wuliuan Stage) fossil deposit in northern Utah and southern Idaho, USA. At present, it is known to preserve 89 species, from at least 10 phyla, of biomineralizing and soft-bodied taxa, and represents the only major Lagerstätte of Wuliuan age in Laurentia outside the Canadian Rockies. In addition to taxonomic diversity, the Spence Shale exposures represent a variety of depositional environments along a continental shelf, which have been affected by several diagenetic events, making it a compelling setting to improve our understanding of taphonomic and diagenetic pathways as they affect the broader Burgess Shale-type (BST) preservation. We present analyses of 28 specimens from six localities using scanning electron microscopy (SEM) and integrated energy dispersive X-ray spectrometry (EDS), together with comparisons of published data. Taxa are predominantly preserved as a combination of carbonaceous compressions, iron oxide and pyrite replacement, but eldoniids of the genus Eldonia consistently show enrichment in rare earth elements (REE). The REE, predominantly lanthanum and cerium, are enriched in the phosphate mineral monazite, which occurs in the inner coil of Eldonia ludwigi . This pattern, seen in all sampled Eldonia , differs from previous reports of REE association in BST preservation in being limited to one tissue type within a specific identifiable taxon. REE enrichment of tissues can occur during the lifetime of an individual or during fossilization, and we present both possible pathways along with an outline of taphonomic processes leading to the preservation of soft-bodied fossils from the Spence Shale. • Main preservation modes are carbonaceous compressions and iron oxides/pyrite. • Phosphatized Eldonia ludwigi have unique REE associations. • Preservation of tissue types is biased, as is found in other Paleozoic Lagerstätten.

Metamorphism obscures primary taphonomic pathways in the early Cambrian Sirius Passet Lagerstätte, North Greenland

Abstract Correct interpretation of soft-bodied fossils relies on a thorough understanding of their taphonomy. While the focus has often been on the primary roles of decay and early diagenesis, the impacts of deeper burial and metamorphism on fossil preservation are less well understood. We document a sequence of late-stage mineral replacements in panarthropod fossils from the Sirius Passet Lagerstätte (North Greenland), an important early Cambrian Burgess Shale–type (BST) biota. Muscle and gut diverticula were initially stabilized by early diagenetic apatite, prior to being pervasively replaced by quartz and then subordinate chlorite, muscovite, and chloritoid during very low- to low-grade metamorphism. Each new mineral replicates the soft tissues with different precision and occurs in particular anatomical regions, imposing strong biases on the biological information retained. Muscovite and chloritoid largely obliterate the tissues’ original detail, suggesting that aluminum-rich protoliths may have least potential for conserving mineralized soft tissues in metamorphism. Overall, the fossils exhibit a marked shift toward mineralogical equilibration with the matrix, obscuring primary taphonomic modes. Sequential replacement of the phosphatized soft tissues released phosphorus to form new accessory monazite (and apatite and xenotime), whose presence in other BST biotas might signal the prior, more widespread, occurrence of this primary mode of preservation. Our results provide critical context for interpreting the Sirius Passet biota and for identifying late-stage overprints in other biotas.

Central nervous system of a 310-m.y.-old horseshoe crab: Expanding the taphonomic window for nervous system preservation

Abstract The central nervous system (CNS) presents unique insight into the behaviors and ecology of extant and extinct animal groups. However, neurological tissues are delicate and prone to rapid decay, and thus their occurrence as fossils is mostly confined to Cambrian Burgess Shale–type deposits and Cenozoic amber inclusions. We describe an exceptionally preserved CNS in the horseshoe crab Euproops danae from the late Carboniferous (Moscovian) Mazon Creek Konservat-Lagerstätte in Illinois, USA. The E. danae CNS demonstrates that the general prosomal synganglion organization has remained essentially unchanged in horseshoe crabs for >300 m.y., despite substantial morphological and ecological diversification in that time. Furthermore, it reveals that the euarthropod CNS can be preserved by molding in siderite and suggests that further examples may be present in the Mazon Creek fauna. This discovery fills a significant temporal gap in the fossil record of euarthropod CNSs and expands the taphonomic scope for preservation of detailed paleoneuroanatomical data in the Paleozoic to siderite concretion Lagerstätten of marginal marine deposits.

A juvenile-rich palaeocommunity of the lower Cambrian Chengjiang biota sheds light on palaeo-boom or palaeo-bust environments.

The fossil record, including the record of Burgess Shale-type deposits, is biased towards late ontogenetic stages. Larval stages, juvenile and subadult specimens exist but are very rare and often preserved as phosphatic fossils, resulting in biased population structures. Here, we report a new Burgess Shale-type Lagerstätte from Haiyan, China. The Haiyan palaeocommunity is extraordinary in that it is rich in fossils of early and middle ontogenetic stages of various phyla, with eggs also commonly found in the studied interval. This Lagerstätte also hosts a considerable number of new taxa-many related to later biotas of Gondwana and Laurentia. We propose that the deposit may either preserve one of the earliest nurseries in the fossil record or, alternatively, records several attempted invasions. Our study highlights the complexity of biotas and their interactions in the lower Cambrian ocean and calls for a better understanding of the mechanisms responsible for the observed spatial variation of fossil community composition in the Cambrian.

The Parker Quarry Lagerstätte of Vermont—The first reported Burgess Shale–type fauna rediscovered

Abstract Soft-bodied fossils of Cambrian age, now known as Burgess Shale–type biotas, were first described from the Parker Slate of the northwest Vermont (USA) slate belt in the late 19th century, 25 years before the discovery of the Burgess Shale in British Columbia, Canada. Here, we report the rediscovery of fossiliferous horizons at Parker's Cobble, the site of the original quarry, which was thought to have been exhausted by excavation. New discoveries include a radiodont, multiple specimens of a new bivalved arthropod, a priapulid, and other undescribed forms. Pervasive soft-sediment deformation suggests accumulation near the toe of a steep unstable slope, similar to the setting of the Burgess Shale. Although fossils are rare, the exceptional preservation of some soft-bodied taxa suggests that recovered diversity was limited by transport into an inhospitable benthic setting rather than by decay, and this implies a potential for future discoveries of new taxa.

Phylogenetic response of naraoiid arthropods to early–middle Cambrian environmental change

AbstractThe Cambrian Period, primarily known for animal life diversifying, experienced global extinctions. Pulses of extinction in Cambrian Series 2 are exemplified by the disappearance of archaeocyath sponges and olenelline and redlichiid trilobites. However, the effect of such extinctions on outer shelf organisms, as typify Burgess Shale‐type (BST) deposits, remains relatively unknown. The phylogeny of naraoiid arthropods, represented in BST deposits globally, has consequently been reconstructed from either side of the Series 2 – Miaolingian extinction event to evaluate the response of offshore marine organisms to Cambrian environmental perturbation. As soft anatomy is known for only a subset of naraoiid species, exoskeletal morphology has proven important. Misszhouia and Naraoia (Naraoia) are distinguished morphometrically by posterior shield length/width and anterior shield length/posterior shield length. Morphometry has also been used to strengthen the identification of some cryptic naraoiid species and revise stratigraphic ranges. A revised naraoiid phylogeny reveals Misszhouia as a monophyletic subgenus, the former genus Pseudonaraoia nests within Naraoia and is placed in synonymy, and the systematic position and status of the Subfamily Liwiinae are sensitive to character weighting. Ten species of Naraoiidae range across the Series 2 – Miaolingian boundary, all naraoiid lineages originating during the main BST window. The persistence of outer shelf naraoiids throughout the Series 2 extinctions suggests that deeper offshore marine environments were resilient to extinction during periods of environmental stress. This study provides novel empirical support for the asylum of BST communities, which may contribute to the taxonomic longevity and widespread geographic distribution of taxa in these biotas.

Early formation and taphonomic significance of kaolinite associated with Burgess Shale fossils

Abstract The role of minerals in Burgess Shale–type fossilization is controversial, particularly that of the clay mineral kaolinite. Kaolinite may have formed on carcasses or attached to them as they decayed, stabilizing organic matter. Alternatively, kaolinite may have formed during metamorphism, playing no role in the preservation of soft tissues. Evaluating the formation and taphonomic role of kaolinite is difficult, because the mineralogy of Burgess Shale–type fossils is incompletely known. We used in situ selected-area X-ray diffraction to constrain the mineralogy of fossils from the classic Burgess Shale Formation in British Columbia, Canada. Fossils can be distinguished from the matrix that surrounds them by the presence of dolomite, kaolinite, and pyrite. Chlorite may be more abundant in the matrix. The preferential survival of kaolinite in association with fossils provides evidence of early diagenetic clay-organic interactions that protected the clay from metamorphic transformation. Kaolinite likely played a crucial role in fossilization, inhibiting the growth of heterotrophic bacteria and aiding polymerization of soft tissue biomolecules. This may result in biases in soft-tissue preservation to areas and times where kaolinite was prevalent.

A new early Cambrian bivalved euarthropod from Yunnan, China and general interspecific morphological and size variations in Cambrian hymenocarines

The hymenocarines were a major and diverse group of euarthropods featured by a bivalved head carapace and a segmented trunk comprising tergo-pleural rings notably from the Cambrian Burgess Shale-type Lagerstätten. Here we document a new ~50 mm long hymenocarine Xiazhuangocaris chenggongensis n. gen. n. sp. from the Xiazhuang fossil assemblage, a slightly younger occurrence of the Chengjiang Lagerstätte within the lower Cambrian Hongjingshao Formation (Cambrian Series 2, Stage 3) in Chenggong, Yunnan, southwestern China. X. chenggongensis is characterized by the bivalved carapace with each valve bearing a protruded anterior tip and a prominent posterior notch, which resembles the P-element of the radiodont Hurdia and is unique among the hymenocarines. The trunk consists of at least 13 tergo-pleural rings including presumably eight abdominal ones terminating in a pair of ovate caudal rami. With the body organization and morphological features closest to waptiids, X. chenggongensis represents a ‘larger’ waptiid-like hymenocarine. The morphometric analysis recognizes the family-level groupings of Cambrian hymenocarines based on the number of tergo-pleural rings and the proportion of exposed trunk length, indicating that these are useful characters for studying hymenocarine morphology and phylogeny. Cambrian hymenocarines exhibited great interspecific body size variations even between sister species of the same family, further suggesting that niche diversification happened on the family level and even among phylogenetically close genera or species during the Cambrian explosion.

Aluminosilicate haloes preserve complex life approximately 800 million years ago.

Mudstone-hosted microfossils are a major component of the Proterozoic fossil record, particularly dominating the record of early eukaryotic life. Early organisms possessed no biomineralized parts to resist decay and controls on their fossilization in mudstones are poorly understood. Consequently, the Proterozoic fossil record is compromised-we do not know whether changing temporal/spatial patterns of microfossil occurrences reflect evolution or the distribution of favourable fossilization conditions. We investigated fossilization within the approximately 1000 Ma Lakhanda Group (Russia) and the approximately 800 Ma Svanbergfjellet and Wynniatt formations (Svalbard and Arctic Canada). Vertical sections of microfossils and surrounding matrices were extracted from thin sections by focused ion beam milling. Elemental mapping and synchrotron-based infrared microspectroscopy revealed that microfossils are surrounded by haloes rich in aluminium, probably hosted in kaolinite. Kaolinite has been implicated in Cambrian Burgess Shale-type (BST) fossilization and is known to slow the growth of degraders. The Neoproterozoic mudstone microfossil record may be biased to tropical settings conducive to kaolinite formation. These deposits lack metazoan fossils even though they share fossilization conditions with younger BST deposits that are capable of preserving non-mineralizing metazoans. Thus metazoans, at least those typically preserved in BST deposits, were probably absent from sedimentary environments before approximately 800 Ma.

Occurrence of the hurdiid radiodontCambrorasterin the middle Cambrian (Wuliuan) Mantou Formation of North China

AbstractThe hurdiid radiodontCambrorasteris characterized by a prominent horseshoe-shaped head carapace, which bears conspicuous posterolateral spinous processes and covers half of the body length, and a pair of frontal appendages possessing rake-like endites. Here we report the discovery of characteristic central and lateral elements as well as a possible appendage endite forCambrorasterfrom the Cambrian Wuliuan Mantou Formation of North China. This discovery suggests thatCambrorasterhad dispersed over a wide biogeographic range and expands the geographic range of Hurdiidae. The increasing discoveries of exceptionally preserved fossils in the Upper Shale Member of the Mantou Formation indicate that this horizon is a promising Burgess Shale–type Lagerstätte.