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306 results for “Early Cambrian”
Pelagiella exigua, an early Cambrian stem gastropod with chaetae: lophotrochozoan heritage and conchiferan novelty
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Small shelly fossils and carbon isotopes from the early Cambrian (Stage 3-4) Mural Formation of western Laurentia
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Data from: Phylogenetic response of naraoiid arthropods to early - middle Cambrian environmental change
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Micro-CT data of two early Cambrian cnidarian fossils from China
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Data from: Periodic shell decollation as an ecology-driven strategy in the early Cambrian Cupitheca
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Three-dimensional morphology of the biramous appendages in Isoxys from the early Cambrian of South China, and its implications for early euarthropod evolution
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Data from: An intermediate type of medusa from the early Cambrian Kuanchuanpu Formation, South China
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Data from: Nature and significance of intraspecific variation in the early Cambrian oryctocephalid trilobite Oryctocephalites palmeri Sundberg and McCollum, 1997
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Data from: The palaeobiological significance of clustering in acritarchs: a case study from the early Cambrian of North Greenland
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Data from: Algal affinity and possible life cycle of the early Cambrian acritarch Yurtusia uniformis from South China
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Data from: Morphometric analysis of Skiagia-plexus acritarchs from the early Cambrian of North Greenland
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The post-embryonic ontogeny of the early Cambrian trilobite Estaingia bilobata from South Australia: trunk development and phylogenetic implications
<p>Trilobites are one of the most diverse and abundant fossil groups from the early Palaeozoic, and as such are useful for answering important questions about early animal evolution, including developmental processes. Ontogenetic information for a large number of trilobite species has been published, but cases where multiple articulated specimens are known across the full range of developmental stages are rare. The early Cambrian (Series 2, Stage 4) Emu Bay Shale biota from Kangaroo Island (South Australia) is numerically dominated by trilobites, particularly articulated specimens of the ellipsocephaloid <i>Estaingia bilobata</i>, which are present in densities of >600 individuals per square metre on certain bedding planes. Here we describe the essentially complete post-embryonic ontogenetic series of <i>E. bilobata</i> from the Emu Bay Shale, and investigate patterns of growth relating to articulation and segmentation in this early Cambrian arthropod. <i>Estaingia bilobata</i> exhibits the hypoprotomeric mode of growth, with the epimorphic phase (the cessation of trunk segment generation) reached prior to the onset of the holaspid period. The meraspid pygidium had an extended equilibrium period where anterior segment release into the thorax was matched by sub-terminal segment generation. Previously undocumented morphological features of <i>E. bilobata</i>, including the hypostome and bispinose pleural tips in holaspides, are also described. The growth characteristics and morphological features of <i>E. bilobata </i>documented herein strengthen close phylogenetic relationships between the Estaingiidae, Ellipsocephalidae and Xystriduridae.</p>
Data from: Small Carbonaceous Fossils (SCFs) from North Greenland: new light on metazoan diversity in early Cambrian shelf environments
<p>The Sirius Passet <i>Lagerstätte</i> of North Greenland provides one of the oldest records of soft-bodied metazoan-dominated ecosystems from within the early Cambrian. The <i>Lagerstätte</i> site itself is restricted to just a single ~1 km-long outcrop located offshore from the shelf margin, in an area that has been affected by metamorphic alteration during the Ellesmerian Orogeny (Devonian–Early Carboniferous). The recent recovery of Small Carbonaceous Fossils (SCFs) to the south in areas that have escaped the effects of this deformation has substantially expanded the known coverage of organic preservation into shallower-water depositional settings in this region. Here we describe additional SCF assemblages from the siliciclastic shelf succession of the Buen Formation (Cambrian Series 2, Stages 3-4; ∼ 515 Ma), expanding upon the previously documented SCF biota. Newly recovered material reveals a rich diversity of non-mineralizing metazoans, chiefly represented by arthropod remains. These include the filtering and grinding elements of a sophisticated crustacean feeding apparatus - the oldest crustacean remains reported to date - alongside an assortment of bradoriid sclerites, including almost complete, three-dimensional valves which tie-together a number of SCFs previously found in isolation. Other metazoan remains include various trilobite cuticles, diverse scalidophoran sclerites, and a range of metazoan fragments of uncertain affinities. This shallower-water assemblage differs substantially from the Sirius Passet biota, which is dominated by problematic euarthropod stem-group members and sponges. Though some of these discrepancies are attributable to taphonomic or temporal factors, these lateral variations in taxonomic composition also point to significant palaeoenvironmental and/or palaeoecological controls on early Cambrian metazoan communities.</p>
Data from: Gut evolution in early Cambrian trilobites and the origin of predation on infaunal macroinvertebrates: evidence from muscle scars in Mesolenellus.
Trilobites are particularly common Cambrian fossils, but their trophic impact on the rapidly evolving marine ecosystems of that time is difficult to assess, due to uncertainties on how diverse their feeding habits truly were. Gut anatomy might help to constrain inferences on trilobite feeding ecology, but preservation of digestive organs is exceedingly rare. Muscle scars on the glabella, known as 'frontal auxiliary impressions' (FAIs), have been interpreted as evidence of the evolution of a pouch-like organ with powerful extrinsic muscles (i.e. a crop) in some trilobites. Here we describe FAIs in Mesolenellus hyperboreus from Cambrian Stage 4 strata of North Greenland, which represents the oldest example of such structures and their first report in the Suborder Olenellina. Mesolenellus FAIs suggest that the crop in trilobites was clearly differentiated from the rest of the digestive tract, and essentially located under a hypertrophied glabellar frontal lobe. Reviews of the digestive anatomy of trilobite sister-taxa and the glabellar morphology of the oldest-known trilobites suggest that the gut of the trilobite ancestor was an essentially simple tract (i.e. no well-differentiated crop) flanked laterally by numerous midgut glands. A crop first evolved in the Cambrian in groups like olenelloids and (later) paradoxidoids. Using ichnological evidence, we hypothesize that the emergence of olenelloids yields evidence for the evolution of predatory inclinations in a group of arthropods originally dominated by surface-deposit-feeders. By allowing the exploitation of a rapidly developing food source, infaunal animals, the diversification of feeding strategies in trilobites might partially explain their unparalleled evolutionary success.
Data from: Developmental biology of the early Cambrian cnidarian Olivooides
Fossilized embryos afford direct insight into the pattern of development in extinct organisms, providing unique tests of hypotheses of developmental evolution based in comparative embryology. However, these fossils can only be effective in this role if their embryology and phylogenetic affinities are well constrained. We elucidate and interpret the development of Olivooides from embryonic and adult stages and use these data to discriminate among competing interpretations of their anatomy and affinity. The embryology of Olivooides is principally characterized by the development of an ornamented periderm that initially forms externally and is subsequently formed internally, released at the aperture, facilitating the direct development of the embryo into an adult theca. Internal anatomy is known only from embryonic stages, revealing two internal tissue layers, the innermost of which is developed into three transversally arranged walls that partly divide the lumen into an abapertural region, interpreted as the gut of a polyp, and an adapertural region that includes structures that resemble the peridermal teeth of coronate scyphozoans. The anatomy and pattern of development exhibited by Olivooides appears common to the other known genus of olivooid, Quadrapyrgites, which differs in its tetraradial, as opposed to pentaradial symmetry. We reject previous interpretations of the olivooids as cycloneuralians, principally on the grounds that they lack a through gut and introvert, in embryo and adult. Instead we consider the affinities of the olivooids among medusozoan cnidarians; our phylogenetic analysis supports their classification as total-group Coronata, within crown-Scyphozoa. Olivooides and Quadrapyrgites evidence a broader range of life history strategies and bodyplan symmetry than is otherwise commonly represented in extant Scyphozoa specifically, and Cnidaria more generally.
Data from: Restricted morphospace occupancy of early Cambrian reef-building archaeocyaths
The evolution of novel morphologies can signify expansion of a clade into new niches. This can be studied in the fossil record by investigating the morphospace occupancy of organisms, with small morphospaces signifying low morphological disparity and more diffuse morphospaces suggesting a broader range of morphologies adapted to different environments. Morphological disparity of many taxa (arthropods, crinoids, etc.) from the Cambrian to modern intervals have been studied in this manner. However, no study has investigated this in archaeocyaths, which, as reef builders, can have a disproportionate effect on early Cambrian biodiversity relative to their frequency. Here, we collect morphological data on archaeocyathan sponges, mostly from Laurentia. Over 600 museum specimens and 400 field samples were measured for traditional morphometric characters as well as discrete gross morphological characteristics. We find that archaeocyaths have an average cup/individual (body) diameter of 10.6 mm. This is significantly smaller than a selected group of modern demosponges and lithistid sponges which measure 94.1 mm and 66.8 mm in diameter respectively and each has a larger size variance. Archaeocyath gross morphologies are also highly constrained to a few simple morphologies (3-6 categories) while modern demosponges and lithistids are more diverse (9 categories each). These data indicate that Laurentian archaeocyaths were restricted in their morphological disparity, potentially due to limitations imposed by having a robust calcareous skeleton while still maintaining a large intervallum cavity space to facilitate passive entrainment. The fact that these Cambrian reef builders were restricted in their morphological complexity may have had a strong influence on the biodiversity of early Phanerozoic ecosystems. Furthermore, a clade limited to only a few specific morphologies is at an increased risk of extinction.
Data from: An early Cambrian chelicerate from the Emu Bay Shale, South Australia
The Emu Bay Shale Lagerstätte (Cambrian Series 2, Stage 4) occurs on the north coast of Kangaroo Island, South Australia. Over 50 species are known from here, including trilobites and non-biomineralized arthropods, palaeoscolecids, a lobopodian, a polychaete, vetulicolians, nectocaridids, hyoliths, brachiopods, sponges and chancelloriids. A new chelicerate, Wisangocaris barbarahardyae gen. et sp. nov., is described herein, based on a collection of some 270 specimens. It is up to 60 mm long, with the length of the cephalic shield comprising about 30% that of the exoskeleton. The cephalic margin has three pairs of bilaterally-symmetrical small triangular spines. A pair of small eyes is placed well forwards on the ventral margin of the cephalic shield. The trunk comprises 11 segments that increase in length while narrowing posteriorly, each possibly bearing a pair of biramous appendages; the most posterior segment is almost square whereas the others are transversely elongated. The spatulate telson is proportionately longer than in taxa such as Sanctacaris, Utahcaris and Leanchoilia. Up to eight (?four pairs) of 3 mm-long elements bearing alternating inward-curving short and long spines beneath the cephalic shield are interpreted as basipodal gnathobases, part of a complex feeding apparatus. A well-developed gut includes a stomach within the cephalic shield; it extends to the base of the telson. In a few specimens there are shell fragments within the gut, including those of the trilobite Estaingia bilobata (the most common species in the biota); these fragments have sharp margins and extend across the gut lumen. The species may have been a predator or a scavenger, ingesting material already broken up by a larger predator/scavenger. The morphology of this taxon shares many overall body features with Sanctacaris, and some with Sidneyia, particularly its gnathobasic complex. These chelicerate affinities are corroborated by phylogenetic analyses.
Data from: Linguliform brachiopods across a Cambrian–Ordovician (Furongian–Early Ordovician) biomere boundary: the Sunwaptan/Skullrockian North American stage boundary in the Wilberns and Tanyard Formations of central Texas
The Cambrian-Ordovician Diversity Plateau, between the Cambrian Explosion and the Ordovician Radiation, is punctuated by a series of well-documented Laurentian trilobite extinction events. These events define the bounding surfaces of trilobite "biomeres" that correspond to North American stages, including those of the Sunwaptan and Skullrockian. Trilobites show a consistent pattern of recovery across these boundaries, and commonly each extinction and replacement of taxa is interpreted as a single event as changing environmental conditions spurred shoreward migration of shelf or oceanic faunas that displaced established cratonic faunas. Linguliform brachiopods are also abundant in strata of this interval, and we investigate their stratigraphic distribution across the Sunwaptan–Skullrockian Stage boundary in Texas through high-resolution stratigraphic sampling of subtidal sediments. We document complete genus- and species-level turnover of the linguliform brachiopod fauna coincident with trilobite extinction events, suggesting that these brachiopods were affected by the same factors that affected trilobites. The Skullrockian replacement fauna was cosmopolitan, with ties to Gondwana and Kazakhstan and to the Laurentian shelf environment. The timing of appearances of taxa suggests that the faunal migration onto the Laurentian shelf came from elsewhere during a transgression. The disappearance of the Sunwaptan fauna and the arrival of the Skullrockian fauna are distinct events. We suggest that "biomere" events may be complex, and the cause of the extinction is not necessarily the same event that facilitates the appearance of a replacement fauna. We describe one new species, Schizambon langei.
Figure 14 in A new arthropod from the Early Cambrian of North Greenland, with a 'great appendage'-like antennula
Figure 14. Potential gut traces of Kiisortoqia soperi gen. et sp. nov., all specimens in dorsal aspect. A, MGUH 28957, showing continuous trace between segmentally arranged hollows. B, MGUH 28968, close-up of posterior part of trunk and tail shield, showing hollow trace with transverse annulation. C, MGUH 28961, close-up of posterior part of trunk, showing a three-dimensionally preserved continuous trace with transverse annulation.
Figure 13 in A new arthropod from the Early Cambrian of North Greenland, with a 'great appendage'-like antennula
Figure 13. Details of axial features of Kiisortoqia soperi gen. et sp. nov. A, MGUH 28955, dorsal aspect, close-up of anterior part of trunk and posterior part of head shield (left), showing putative muscle tissue in association with transverse hollows; B, MGUH 28966, ventral aspect, close-up of middle part of trunk, showing corrugated surface with transverse interruptions, the arrows point to exsagittal mineralizations. C, MGUH 28959, dorsal aspect, showing segmentally arranged, putative midgut diverticulae, the radial orientation of planar elements is seen in the anterior two trunk segments, and the sagittal orientation is seen in the posterior trunk segments. D, MGUH 28944, dorsal aspect, showing hollows after segmentally arranged axial mineralizations.
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Allen Brain Atlas
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Annotated Behaviour and Observability Dataset (ABODe)
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