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Biomineralization around the Ediacaran–Cambrian boundary enabled new ecological strategies, including encrustation, boring and cavity-dwelling, across various lineages. Here we describe problematic vesicular fossils that are attached to, or embedded within, the calcium phosphatic shells of the tommotiid genus Tesella from the middle Cambrian Henson Gletscher Formation of North Greenland. Despite their simple morphology, the combination of characteristics such as size, shape, presence of an invagination, habitat, and clustering behaviour, suggests that these fossils are best interpreted as colonizing microbes in a biological relationship with the tommotiid. We explore potential affinities of these vesicular microfossils, including comparisons to parasitic fungi such as Chytridiomycota (‘chytrids’). We describe a new genus and species, Avannacystis polaris, which provides new insights into early biological interactions, and substrate colonization in Cambrian ecosystems.

Aculifera, comprising Polyplacophora (chitons) and Aplacophora, is one of two major molluscan clades, characterised by a scleritome of mineralised sclerites or plates. Their early evolutionary history is poorly understood due to sparse fossil records bridging possible Terreneuvian (early Cambrian) stem-group taxa and Furongian (late Cambrian) chiton-like articulated representatives. Here, we describe seven species in five genera from the Aftenstjernes & oslash; Formation (Cambrian Series 2, Stage 4) of North Greenland, including a second species, Qaleruaqia bronlundensis sp. nov., of the oldest paleoloricate, Qaleruaqia sp.; the sachitid Hippopharangites groenlandicus, Hippopharangites? sp.; a possible intermediate plate of a chiton-like scleritome, Avannaplax midsommersoensis gen. et sp. nov.; and possible aculiferans Ocruranus? kangerluk and Xianfengella yatesi. Morphological comparisons of the North Greenland assemblage reveal strong affinities with Terreneuvian taxa, including maikhanellids and the Ocruranus-Eohalobia group, supporting their interpretation as stem-group aculiferans. A palaeobiogeographic analysis using 650 global occurrences of Cambro-Ordovician taxa shows that the Ægir Ocean as a principal dispersal corridor for early diversification of aculifera. During the Terreneuvian, aculiferans were widespread along Ægir margins but rare in Laurentia, likely due to isolation by the Iapetus Ocean. From Cambrian Series 2 onward, increased connectivity and expanded low-latitude carbonate platforms fostered diversification in eastern Laurentia, including North Greenland. This assemblage from North Greenland bridges a critical spatio-temporal and morphological gap between the earliest Cambrian taxa and Furongian paleoloricates, offering new insight into aculiferan diversification and palaeobiogeography.

Elements of Fimbulispina laurentica gen. et sp. nov. from the Fimbuldal Formation (middle Cambrian, Miaolingian Series, Drumian Stage) of North Greenland (Laurentia) are interpreted as the circum-oral grasping spines of a stem-group chaetognathiferan. Association of the elements into the arrays known from fossil and recent free swimming chaetognathans (arrow worms) has not been observed. The elements differ from the simple, hollow, cones characteristic of contemporaneous protoconodont elements in displaying a transversely convex posterior face, a deeply channelled anterior face, a pair of internal lath-like structures and two basal cavities. In terms of their overall cross-section they are reminiscent of elements of Dakorhachis thambus from the Weeks Formation (Miaolingian Series) of Utah. Seen collectively, the morphological variation displayed by these elements attests to the diversity of 'graspers' in stem-group chaetognathiferans.John S. Peel [john.peel@pal.uu.se], Department of Earth Sciences (Palaeobiology), Uppsala University, Villav & auml;gen 16, Uppsala, SE-75236, Sweden.

The fauna preserved in decalcified sandstones of the S ae terdal Formation (Cambrian Stage 4) of southern Peary Land, North Greenland (Laurentia) is dominated by the trilobites Kootenia marcoui and Bonnia brennus, which also occur in the equivalent dark carbonates and mudstones of the Henson Gletscher Formation to the west. They are associated with Olenellus and small ptychoparioid trilobites. Brachiopods compared to Nisusia ancauchensis, originally described from the Precordillera terrane in Argentina, show variation in shell morphology and the form of the pseudodeltidium. They occur together with Kutorgina cf. cingulata, which is conspicuous in the overlying Paralledal Formation, rare Matutella sp. and an indeterminate hyolithid.

Acid residues from the Henson Gletscher Formation of North Greenland have yielded the most diverse assemblage of Small Shelly Fossils (SSF) known from the middle Cambrian (Miaolingian Series) of Laurentia. The fossils derive from the Wuliuan Stage (Ptychagnostus gibbus Biozone; Topazan Regional Stage of North America) and compare with faunas from the Ordian-Templetonian regional stages of Australia and the Kuonamka Formation of Northern Siberia, making a valuable contribution to world-wide early Miaoliongian correlation. The assemblage is dominated by 21 species of helcionelloid molluscs, a third of which are referred to Dorispira Parkhaev, 2010. Mellopegma Runnegar & Jell, 1976 and Erugoconus Peel & Kouchinsky, 2022, are also conspicuous. Hyoliths include the operculate Protowenella Runnegar & Jell, 1976, Crestjahitus Sysoev, 1968 and Yuku? Kruse, 2002. Diverse form taxa of sponge spicules are also well represented in Siberia and Australia. The phosphatocopid Dabashanella Huo, Shu, & Fu, 1983, well known from China, is abundant. Diagenetic phosphatization of soft parts is common in bivalved arthropods, but rare cases include Dietericambria Peel, 2022a, the oldest known pentastomid, and a priapulid larva. Preservation as phosphatic internal moulds is otherwise characteristic. Multiaxial organisms include cnidarians and epiphytiform taxa of uncertain position. The stem group octocoral Cambroctoconus Park, Woo, Lee, Lee, Lee, Han, Chough & Choi, 2011, described from China and Kyrgyzstan, is common. Bromalites and casts of euendolith galleries are abundant and diverse in form. New taxa: Crestjahitus groenlandicus sp. nov., Dabashanella? lunaiformis sp. nov., Hensonidendra tavsenica gen. et sp. nov., Hensonidendra hensoniensis gen. et sp. nov., Laugephakos groenlandicus gen. et sp. nov., Liangshanella? qassutit sp. nov., Tavsenicoralla avannaa gen. et sp. nov.

Ressericonella gen. nov., a new genus of helcionelloid mollusc, characterized by a narrow shell with a shallowly convex dorsal surface and flat to shallowly concave lateral areas, is described from the Cambrian of Greenland and Idaho. The type species is Helcionella aequa Resser, 1939 from the Langston Formation (Naomi Peak Limestone Member) of early middle Cambrian age (Miaolingian Series, Wuliuan Stage, Albertella Biozone). Ressericonella pipalukae gen. et sp. nov. occurs in the latest early Cambrian (Cambrian Series 2, Stage 4, Bonnia-Pagetides elegans Biozone) of southern Freuchen Land, North Greenland. Silicified specimens of Ressericonella pipalukae from North Greenland preserve two-layered shell structure in which an inner layer with a transverse fibrous pattern similar to lamello-fibrillar structure is overlain by an outer layer with fine threads radiating from the apex.

Borings of microscopic organisms (euendoliths) are described from the Henson Gletscher Formation (middle Cambrian, Miaolingian Series, Wuliuan Stage) of Peary Land, North Greenland (Laurentia). Partially phosphatised sclerites of Chancelloria and valves of the brachiopod Nisusia reveal abundant casts of borings following dissolution of skeletal calcium carbonate in weak acetic acid. Threads referred to Scolecia dominate, occurring together with coccoids (Planobola) and the branching Fascichnus, in a suite comparable to a lower Cambrian assemblage from the Maidiping Formation of Sichuan, China.

Helcionelloid molluscs are described from the Gislov Formation (Cambrian Series 2, Stage 4; Vergalian-Rausvian regional stages) in Scania, southern Sweden. Seven species are distinguished,including ‛Pelagiella' sp., Helcionella antiqua, Davidonia puppis, Davidonia cf. rostrata, Latouchella cf. costata, Stenotheca norvegica, and an indeterminate helcionelloid. The c. 750 specimens were collected from a 30 cm interval with a diverse shelly fauna, encompassing the Ellipsostrenua spinosa Zone. The peak distribution of the molluscs is within the 2-3 mm size class, and there was limited sorting or transport prior to burial. Helcionella antiqua is characteristic of the helcionelloid assemblage, and together with Davidonia puppis, the only molluscs in the assemblage exceeding 10 mm in length. All species except 'Pelagiella' display full ontogenetic series providing verification of morphological transitions and direct ontogenetic ties between small helcionelloid juveniles or embryonic shells and their macro adults. Analysis of distributions indicates that the Gislov assemblage is closely comparable to the Evjevik Member of the Mjosa area, Norway, while sections in northern Sweden form a separate cluster. The distribution of the shelly assemblage in the E. spinosa Biozone is consistent with a temporal distribution of this fauna, rather than biofacies control.

The Portfjeld Formation, as originally defined, is the lowermost lithostratigraphic unit of the mainly Lower Palaeozoic Franklinian Basin in southern Peary Land, central North Greenland. The unit crops out semi-continuously from Valdemar Glückstadt Land to Nordenskiöld Fjord but is also recognised locally in northern parts of Peary Land and Wulff Land (western North Greenland). Regionally, it provides a key record of the early, pre-break-up history of the basin. The type succession in southern Peary Land has thus been the focus of recent biostratigraphical, sedimentological and geochemical study. This has demonstrated the composite nature of the unit, a lower interval (c. 190 m thick) of carbonate ramp deposits of Neoproterozoic (late Ediacaran) age being overlain at a karstic unconformity by a shallow marine, mixed carbonate–siliciclastic interval (c. 100 m thick) of probable earliest Cambrian age. Lithostratigraphic revision of this succession is presented here. The Portfjeld Formation throughout North Greenland is elevated to the rank of group, and two new formations are defined in this group in southern Peary Land and immediately adjacent areas: the Ediacaran carbonate-dominated unit is referred to the Slusen Formation, the upper mixed siliciclastic–carbonate unit to the Glaciologelv Formation.

The periostracum, a non-calcified organic layer that envelops the mineralized shell layer ('ostracum') of molluscs, acts as an initial framework for the calcified 'ostracum.' Despite its significance in biomineralization in molluscs, fossil examples of the periostracum are limited in the geological record, especially from the Palaeozoic era, due to its susceptibility to post-mortem decay. In this study, we describe radial threads found on the outer surface of Cambrian molluscs, including helcionelloids and rostroconchs, which we interpret as fossilized periostracal structures. These radial threads are observed in 13 species from five valid genera, exhibiting a widespread palaeogeographical distribution encompassing Gondwana (Australia), Siberia, western Laurentia (Utah), and eastern Laurentia (Greenland), and spanning Cambrian Stage 4-Drumian deposits. These radial threads always cover the outermost surface of shells, dividing it into regular intervals, and develop through incremental growth. They originate from the apical area of helcionelloids or the umbo of rostroconchs. Detailed examination has revealed that the radial threads initiate at the apical region, but may be absent from the protoconch (embryonic shell). The radial threads are most likely preserved by mineral encrustation on the periostracum. Similar, but not homologous, radial threads are found in other fossil and modern molluscan taxa, such as the adhesive radial lines of anomalodesmatan bivalves or the periostracal ridges of viviparid gastropods.