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opencc-zeroSep 2024View details →

FIG. 4 in New archaeocyath genus from the early Cambrian of the western Anti-Atlas, Morocco

FIG. 4. — Fouanoucyathus tafraoutiensis El Bakhouch & Kerner, n. gen., n. sp., paratype AA-FOU-CI-4 from FO.IS24: A, transverse view of specimen prior to preparation; B, detail of transverse section showing inner wall porosity and synapticulae (central cavity at upper left); C, detail of longitudinal section showing septal porosity and inner wall canals (central cavity at right); D, detail of longitudinal section showing outer wall canals. Scale bars: A, 7.5 mm; B, 0.3 mm; C, 1 mm; D, 0.6 mm.

opencc-zeroSep 2024View details →

FIG. 3 in New archaeocyath genus from the early Cambrian of the western Anti-Atlas, Morocco

FIG. 3. — Fouanoucyathus tafraoutiensis El Bakhouch & Kerner, n. gen., n. sp., paratype AA-FOU-CI-3 from FO.IS10: A, transverse view of specimen prior to preparation; B, detail of longitudinal section showing walls, septal porosity and synapticular tabulae (inner wall at left); C, detail of longitudinal section showing inner wall canals (central cavity at left); D, detail of longitudinal section showing outer wall canals and synapticular tabulae (intervallum at right). Scale bars: A, 8.5 mm; B, 2 mm; C, 1 mm; D, 0.5 mm.

Fig. 6 in Trunk ornament on the palaeoscolecid worms Cricocosmia and Tabelliscolex from the Early Cambrian Chengjiang deposits of China

Fig. 6. Reconstructions of the palaeoscolecid worms Cricicosmia and Tabelliscolex (modified from Huang 2005b). A. Cricocosmia jinningensis; A1, whole animal; A2, typical lateral sclerite of Cricocosmia jinningensis. B. Tabelliscolex hexagonus. C. Tabelliscolex maanshanensis sp. nov.

Fig. 3 in Trunk ornament on the palaeoscolecid worms Cricocosmia and Tabelliscolex from the Early Cambrian Chengjiang deposits of China

Fig. 3. Element maps of Cricocosmia jinningensis Hou and Sun, 1988 from the Early Cambrian of Chengjiang, China show that the lateral sclerites of Cricocosmia have elevated content of oxygen and ferrum and depleted silicon and aluminium compared with other areas of the trunk. A small amount of phosphorus is present on the surface of the trunk, possibly indicating the presence of apatite. The first image is of the anterior cone−shaped sclerites shown in Fig. 2A2, ELI−0001402.

Fig. 5 in Trunk ornament on the palaeoscolecid worms Cricocosmia and Tabelliscolex from the Early Cambrian Chengjiang deposits of China

Fig. 5. Element maps of Tabelliscolex maanshanensis sp. nov. from the Early Cambrian Chengjiang deposits, China. Mapping area is the upper right part in Fig. 4A1, ELI−0001219. Images show that lateral sclerites of Tabelliscolex maanshanensis are composed predominantly of silicon, oxygen, and aluminum, with lesser amounts of iron, potassium, and magnesium.

Fig. 4 in Trunk ornament on the palaeoscolecid worms Cricocosmia and Tabelliscolex from the Early Cambrian Chengjiang deposits of China

Fig. 4. SEM−BSE images of uncoated specimens of Tabelliscolex from the Early Cambrian of Chengjiang, China. A. Tabelliscolex maanshanensis sp. nov., ELI−0001219, holotype; A1, molted elongate sclerites; A2, shows the tubercles and the pits on the inner side; A3, showing each pit has a inner circlet of concentric laminae; A4, close−up showing the pit and the inner lamina. B. Tabelliscolex hexagonus Han, Zhang, and Shu, 2003a, ELI−0001218, holotype; B1, two over−lapping plates, one plate showing the tubercles (B2) and another showing the pits (B3); B4, the skeleton of the plate, noting the framboidal pyrites within the skeleton; B5, close−up showing framboidal pyrites replicated by finer minerals (B6); B7, close−up of the pit; B8, some needle−like minerals within the pit in B7.

Fig. 2 in Trunk ornament on the palaeoscolecid worms Cricocosmia and Tabelliscolex from the Early Cambrian Chengjiang deposits of China

Fig. 2. Diagrammatic presentation of the trunk ornamentation in Cricocosmia jinningensis Hou and Sun, 2003 from the Earlyn Cambrian Chengjiang deposits, China. A. ELI−0001402, lateral spines from the anterior trunk (rectangle area in Fig. 1C); A1, one of the plate−shape sclerites with a net structure; the anterior part of the sclerites is broken; A2, one of the cone−shaped sclerites with net−like structure; note the size of the circlet decreases distally; A3, showing the net−like structure; A4, the net−like structure consists of numerous finer spiculate minerals; A5, trunk cuticle surrounding the sclerite consists of bright larger octahedral pyrites, which are also composed of numerous micro−spiculate minerals. B. ELI−0001403, lateral spines from the posterior trunk; B1, the lateral sclerites showing a bright white high−contrast colour with surrounding trunk cuticle (rectangle area in Fig. 1D); B2, a lateral spine consisting of many tubercles; B3, showing the tubercles. C. ELI−0001404, showing the lateral sclerites with tubercles.

Fig. 1. Early Cambrian palaeoscolecid worms from the Early Cambrian Chengjiang deposits, China. A–E in Trunk ornament on the palaeoscolecid worms Cricocosmia and Tabelliscolex from the Early Cambrian Chengjiang deposits of China

Fig. 1. Early Cambrian palaeoscolecid worms from the Early Cambrian Chengjiang deposits, China. A–E. Cricocosmia jinningensis Hou and Sun, 1988. A. ELI−0001400, showing the ventral trunk spines (arrow) of Cricocosmia. B. ELI−0001401, showing the ventral trunk spines (arrow); B2 is the rectangle area on B1. C. ELI−0001402; C1, a complete specimen; C2, lateral spines at the anterior portion of the trunk (rectangle area in C1) preserved fine structure; C3, showing the preserved microstructure of the lateral spines, note that sclerites colored black can preserve finer structure than those of yellow, and that sclerites showing finer structures are apparently dislocated probably due to molting. D. ELI−0001403; D1, a complete specimen; D2, posterior portion of the body (rectangle area in D1) with several spines (arrows pointed) bearing fine structures. E. ELI−0001404; E1, a fragmental specimen in burrowing; E2, showing the trunk sclerites (arrows pointed) with a net−like structure; the marginal ridges are evident on these sclerites. F. Tabelliscolex hexagonus Han, Zhang, and Shu, 2003a, ELI−0001218, holotype, showing the general outline. G. Tabelliscolex maanshanensis sp. nov., ELI−0001219, showing molted trunk sclerites.

opencc-zeroMay 2023View details →

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Cambrian origin but no early burst in functional disparity for Class Bivalvia

Both the Cambrian Explosion, more than half a billion years ago, and its Ordovician aftermath some thirty-five million years later, are often framed as episodes of widespread ecological opportunity, but not all clades originating during this interval showed prolific rises in morphological or functional disparity. In a direct analysis of functional disparity, instead of the more commonly used proxy of morphological disparity, we find that ecological functions of Class Bivalvia arose concordantly with and even lagged behind taxonomic diversification, rather than the early-burst pattern expected for clades originating in supposedly open ecological landscapes. Unlike several other clades originating in the Cambrian Explosion, the bivalves' belated acquisition of key anatomical novelties imposed a macroevolutionary lag, and even when those novelties evolved in the Early Ordovician, functional disparity never surpassed taxonomic diversity. Beyond this early period of animal evolution, the founding and subsequent diversification of new major clades and their functions might be expected to follow the pattern of the early bivalves—one where interactions between highly dynamic environmental and biotic landscapes and evolutionary contingencies need not promote prolific functional innovation.

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Cambrian origin but no early burst in functional disparity for Class Bivalvia

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publicMay 2023View details →

opencc-zeroMay 2020View details →

Data from: An intermediate type of medusa from the early Cambrian Kuanchuanpu Formation, South China

The tetraradial or pentaradial fossil embryos and related hatched individuals from the early Cambrian Kuanchuanpu Formation are of great interest for understanding the early evolution of medusozoans. The phylogenetic and evolutionary significance of their external and internal characters (e.g. manubrium, tentacles, septa and claustra) is still controversial. Here we describe a new pentamerous medusozoan, Hanagyroia orientalis gen. et sp. nov., characterized by five well-developed perradial oral lips around a remarkably large manubrium, a conspicuous equatorial groove, and five short interradial pairs of extensile tentacles at the bell margin. Internally, five broad and stout interradial septa join horizontally to form the claustra. Hanagyroia orientalis lacks the frenula, apertural lappet and velarium seen in coeval microfossils and extant cubozoans. Although H. orientalis resembles extant coronate scyphozoans in its round medusa-like bell margin and equatorial groove, cladistic analysis suggests close affinity with cubozoans. Hanagyroia may represent an intermediate morphological type between scyphozoans and cubozoans. The well-developed oral lips and paired short strong tentacles of Hanagyroia suggest direct development.

opencc-zeroFeb 2020View details →

Small shelly fossils and carbon isotopes from the early Cambrian (Stage 3-4) Mural Formation of western Laurentia

The extraordinary window of phosphatised and phosphatic Small Shelly Fossils (SSFs) during the early and middle Cambrian is an important testament to the radiation of biomineralising metazoans. While SSF are well known from most Cambrian palaeocontinents during this time interval, western Laurentia has relatively few SSF faunas. Here we describe a diverse SSF fauna from the early Cambrian (Stage 3-4) Mural Formation at three localities in Alberta and British Columbia, Canada, complemented by carbon isotope measurements at two of the recorded sites to aid in a potential future bio-chemostratigraphic framework.. The fauna expands the recorded SSF assemblage diversity in western Laurentia and includes several brachiopods, four bradoriids, three chancelloriids, two hyoliths, a tommotiid and a helcionellid mollusc as well as echinoderm ossicles and specimens of Microdictyon, Volborthella and Hyolithellus. New taxa include the tommotiid genus Canadiella gen. nov., the new bradoriid species Hipponicharion perforata sp. nov. and Pseudobeyrichona taurata sp. nov. Compared to contemporaneous faunas from western Laurentia, the fauna is rich, particularly in taxa with originally phosphatic shells, which appear to be associated with archaeocyathid buildups. This suggests that the generally low faunal diversity in western Laurentia may be at least partly a consequence of poor sampling of suitable archaeocyathan reef environments. In addition, the tommotiid Canadiella filigrana appears to be of biostratigraphic significance in Cambrian Stage 3 strata of western Laurentia and the unexpected high diversity of bradoriid arthropods in the fauna also suggests that this group may prove useful for biostratigraphic resolution in the region.

opencc-zeroNov 2020View details →

Data from: Phylogenetic response of naraoiid arthropods to early - middle Cambrian environmental change

The 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 phylogeny for naraoiids 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 through the Series 2–Miaolingian boundary, all naraoiid lineages originating during the main BST window. The persistence of outer shelf naraoiids through the Series 2 extinctions suggests that deeper offshore marine environments were resilient to extinction during periods of environmental stress. This study therefore 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.

opencc-zeroNov 2019View details →

Data from: Periodic shell decollation as an ecology-driven strategy in the early Cambrian Cupitheca

Shell decollation is a growth strategy that has been adopted by a number of invertebrate taxa to offset the metabolic and ecological disadvantages of shell growth. However, little is known about the origin and evolution of this process. We here describe well-preserved specimens of the hyolith, Cupitheca decollata sp. nov., preserving the decollation process from the early Cambrian Yu'anshan Formation (ca. 518 million years ago) of South China. Based on a large number of specimens collectively representing different developmental stages, we use high-resolution X-ray microtomography and scanning electronic microscopy to reconstruct the process of decollation in this taxon. Cupitheca is among the earliest known small shelly fossils, and thus our discovery confirmed that periodic decollation had evolved by the onset of the Cambrian explosion, reflecting the high intensity of the predator-prey arms race in early Cambrian ecosystems. A comparison between the decollation processes of Cupitheca and other shelly invertebrates suggests that periodic decollation and the associated molecular mechanisms of calcium dissolution, uptake, allocation, and deposition may have had multiple independent origins.Shell decollation is a growth strategy that has been adopted by a number of invertebrate taxa to offset the metabolic and ecological disadvantages of shell growth. However, little is known about the origin and evolution of this process. We here describe well-preserved specimens of the hyolith, Cupitheca decollata sp. nov., preserving the decollation process from the early Cambrian Yu'anshan Formation (ca. 518 million years ago) of South China. Based on a large number of specimens collectively representing different developmental stages, we use high-resolution X-ray microtomography and scanning electronic microscopy to reconstruct the process of decollation in this taxon. Cupitheca is among the earliest known small shelly fossils, and thus our discovery confirmed that periodic decollation had evolved by the onset of the Cambrian explosion, reflecting the high intensity of the predator-prey arms race in early Cambrian ecosystems. A comparison between the decollation processes of Cupitheca and other shelly invertebrates suggests that periodic decollation and the associated molecular mechanisms of calcium dissolution, uptake, allocation, and deposition may have had multiple independent origins.

opencc-zeroApr 2022View details →

Data from: Morphometric analysis of Skiagia-plexus acritarchs from the early Cambrian of North Greenland

The Cambrian evolutionary radiations are marked by spectacular biotic turnovers and the establishment of increasingly tiered food chains. At their base are primary producers, which in the Cambrian fossil record are chiefly represented among organic-walled microfossils. The majority of these microfossil remains have traditionally been attributed to an informal category of incertae sedis called "acritarchs", based entirely on form taxonomy. Acritarch form-taxa have been intensely used for biostratigraphy, and in large-scale studies of phytoplankton diversity. However, both prospects have been challenged by cases of taxonomic inconsistencies and over-splitting arising from the large phenotypic plasticity seen among these microfossils. The acritarch form-genus Skiagia stands as an ideal case-study to explore these taxonomic challenges, since it encompasses a number of form-species widely used in lower Cambrian biostratigraphy. Moreover, subtle morphological differences among Skiagia species were suggested to underlie key evolutionary innovations towards complex reproduction strategies. Here we apply a multivariate morphometric approach to investigate the morphological variation of Skiagia-plexus acritarchs using an assemblage sourced from the Buen Formation (Cambrian Series 2, Stage 3–4) of North Greenland. Our analysis showed that the specific-level classification of Skiagia discretizes a continuous spectrum of morphologies. While these findings bring important taxonomic and biostratigraphic hurdles to light, the unequal frequency distribution of life cycle stages among Skiagia species suggests that certain elements of phytoplankton paleobiology are nonetheless captured by Skiagia form-taxonomy. These results demonstrate the value of using morphometric tools to explore acritarch phenotypic plasticity and its potential ontogenetic and paleoecological drivers in Cambrian ecosystems.

opencc-zeroMar 2020View details →

Pelagiella exigua, an early Cambrian stem gastropod with chaetae: lophotrochozoan heritage and conchiferan novelty

Exceptionally well-preserved impressions of two bundles of bristles protrude from the apertures of small, spiral shells of Pelagiella exigua, recovered from the Kinzers Formation (Cambrian, Stage 4, "Olenellus Zone", ~ 512 Ma) of Pennsylvania. These impressions are inferred to represent clusters of chitinous chaetae, comparable to those borne by annelid parapodia and some larval brachiopods. They provide an affirmative test in the early metazoan fossil record of the inference, from phylogenetic analyses of living taxa, that chitinous chaetae are a shared early attribute of the Lophotrochozoa. Shells of Pelagiella exhibit logarithmic spiral growth, microstructural fabrics, distinctive external sculptures, and muscle scars characteristic of molluscs. Hence, Pelagiella has been regarded as a stem mollusc, a helcionelloid expressing partial torsion, an untorted paragastropod, or a fully torted basal member of the gastropod crown group. The inference that its chaeta-bearing appendages were anterior-lateral, based on their probable functions, prompts a new reconstruction of the anatomy of Pelagiella, with a mainly anterior mantle cavity. Under this hypothesis, two lateral-dorsal grooves, uniquely preserved in Pelagiella atlantoides, are interpreted as sites of attachment for a long left ctenidium and a short one, anteriorly on the right. The orientation of Pelagiella and the asymmetry of its gills, comparable to features of several living vetigastropods, nominate it as the earliest fossil mollusc known to exhibit evidence of the developmental torsion characteristic of gastropods. This key adaptation facilitated an evolutionary radiation, slow at first and rapid during the Ordovician that gave rise to the remarkable diversification of the Gastropoda.

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FIGURE 6 in Chuandianella ovata: An early Cambrian stem euarthropod with feather-like appendages

FIGURE 6. Reconstruction of Chuandianella ovata in vivo.

opencc-by-4.0Dec 2022View details →

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FIGURE 9 in A new euarthropod with large frontal appendages from the early Cambrian Chengjiang biota

FIGURE 9. Artistic reconstruction of Fengzhengia mamingae gen. et sp. nov.

opencc-by-4.0Dec 2022View details →

opencc-zeroApr 2023View details →

Three-dimensional morphology of the biramous appendages in Isoxys from the early Cambrian of South China, and its implications for early euarthropod evolution

Early euarthropod evolution involved a major transition from lobopodian-like taxa to organisms featuring a segmented, well-sclerotized trunk (arthrodization) and limbs (arthropodization). However, the precise origin of a completely arthrodized trunk and arthropodized ventral biramous appendages remain controversial, as well as the early onset of anterior-posterior limb differentiation in stem-group euarthropods. New fossil material and micro-computed tomography inform the detailed morphology of the arthropodized biramous appendages in the carapace-bearing euarthropod Isoxys curvirostratus from the early Cambrian Chengjiang biota. In addition to well-developed grasping frontal appendages. I. curvirostratus possesses two batches of morphologically and functionally distinct biramous limbs. The first batch consists of four pairs of short cephalic appendages with robust endites with a feeding function, whereas the second batch has more elongate trunk appendages for locomotion. Critically, our new material shows that the trunk of I. curvirostratus was not arthrodized. The results of our phylogenetic analyses recover isoxyids as some of the earliest branching sclerotized euarthropods, and strenghens the hypothesis that arthropodized biramous appendage evolved before full body arthrodization.