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Jean-bernard Caron - One of the best experts on this subject based on the ideXlab platform.
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A possible case of inverted lifestyle in a new bivalved arthropod from the Burgess Shale.
Royal Society open science, 2019Co-Authors: Alejandro Izquierdo-lópez, Jean-bernard CaronAbstract:The origin of the arthropod carapace, an enlargement of cephalic tergites, can be traced back to the Cambrian Period. However, its disparity and evolution are still not fully understood. Here, we d...
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Demecology in the Cambrian: synchronized molting in arthropods from the Burgess Shale.
BMC biology, 2013Co-Authors: Joachim T. Haug, Jean-bernard Caron, Carolin HaugAbstract:Background The Burgess Shale is well known for its preservation of a diverse soft-bodied biota dating from the Cambrian Period (Series 3, Stage 5). While previous paleoecological studies have focused on particular species (autecology) or entire paleocommunities (synecology), studies on the ecology of populations (demecology) of Burgess Shale organisms have remained mainly anecdotal.
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Tubicolous enteropneusts from the Cambrian Period
Nature, 2013Co-Authors: Jean-bernard Caron, Simon Conway Morris, Christopher B. CameronAbstract:Examination of a fossil enteropneust, Spartobranchus tenuis (Walcott, 1911), from the Cambrian-Period Burgess Shale shows that they looked similar to modern enteropneusts but lived in tubes, like modern pterobranchs; the findings shed light on the common ancestor of enteropneusts and pterobranchs, and hence the origin of chordates. Hemichordates are a marine group that, apart from one monospecific pelagic larval form, are represented by the vermiform enteropneusts and minute colonial tube-dwelling pterobranchs. Together with echinoderms, they comprise the clade Ambulacraria^ 1 . Despite their restricted diversity, hemichordates provide important insights into early deuterostome evolution, notably because of their pharyngeal gill slits^ 2 . Hemichordate phylogeny has long remained problematic^ 3 , 4 , not least because the nature of any transitional form that might serve to link the anatomically disparate enteropneusts and pterobranchs is conjectural. Hence, inter-relationships have also remained controversial. For example, pterobranchs have sometimes been compared to ancestral echinoderms^ 1 . Molecular data identify enteropneusts as paraphyletic, and harrimaniids^ 5 , 6 , 7 , 8 as the sister group of pterobranchs. Recent molecular phylogenies suggest that enteropneusts are probably basal within hemichordates, contrary to previous views^ 9 , but otherwise provide little guidance as to the nature of the primitive hemichordate^ 7 , 8 . In addition, the hemichordate fossil record is almost entirely restricted to peridermal skeletons of pterobranchs, notably graptolites^ 10 , 11 . Owing to their low preservational potentials, fossil enteropneusts are exceedingly rare^ 12 , 13 , 14 , 15 , and throw no light on either hemichordate phylogeny or the proposed harrimaniid–pterobranch transition. Here we describe an enteropneust, Spartobranchus tenuis (Walcott, 1911), from the Middle Cambrian-Period (Series 3, Stage 5) Burgess Shale. It is remarkably similar to the extant harrimaniids, but differs from all known enteropneusts in that it is associated with a fibrous tube that is sometimes branched. We suggest that this is the precursor of the pterobranch periderm, and supports the hypothesis that pterobranchs are miniaturized and derived from an enteropneust-like worm^ 5 , 6 . It also shows that the periderm was acquired before size reduction and acquisition of feeding tentacles, and that coloniality emerged through aggregation of individuals, perhaps similar to the Cambrian rhabdopleurid Fasciculitubus ^ 11 . The presence of both enteropneusts and pterobranchs in Middle Cambrian strata, suggests that hemichordates originated at the onset of the Cambrian explosion. Enteropneusts, or acorn worms, are mud-dwelling creatures that live from the foreshore down to the deep ocean. They are related to pterobranchs, small, colonial, tube-dwelling animals that superficially look completely different. Both are related to echinoderms (starfish and allies) and chordates — the group of animals that includes ourselves. Here Jean-Bernard Caron and colleagues describe fossil enteropneusts from the famous Cambrian Burgess Shale of British Columbia. They look much like some modern enteropneusts, but lived in tubes, more like modern pterobranchs. This adds to the diversity of the fossil fauna and gives pointers to what the common ancestor of enteropneusts and pterobranchs looked like. It might also fuel the debate about whether the ancestor of chordates was a free-living worm, or a sessile, colonial creature.
Christopher B. Cameron - One of the best experts on this subject based on the ideXlab platform.
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Tubicolous enteropneusts from the Cambrian Period
Nature, 2013Co-Authors: Jean-bernard Caron, Simon Conway Morris, Christopher B. CameronAbstract:Examination of a fossil enteropneust, Spartobranchus tenuis (Walcott, 1911), from the Cambrian-Period Burgess Shale shows that they looked similar to modern enteropneusts but lived in tubes, like modern pterobranchs; the findings shed light on the common ancestor of enteropneusts and pterobranchs, and hence the origin of chordates. Hemichordates are a marine group that, apart from one monospecific pelagic larval form, are represented by the vermiform enteropneusts and minute colonial tube-dwelling pterobranchs. Together with echinoderms, they comprise the clade Ambulacraria^ 1 . Despite their restricted diversity, hemichordates provide important insights into early deuterostome evolution, notably because of their pharyngeal gill slits^ 2 . Hemichordate phylogeny has long remained problematic^ 3 , 4 , not least because the nature of any transitional form that might serve to link the anatomically disparate enteropneusts and pterobranchs is conjectural. Hence, inter-relationships have also remained controversial. For example, pterobranchs have sometimes been compared to ancestral echinoderms^ 1 . Molecular data identify enteropneusts as paraphyletic, and harrimaniids^ 5 , 6 , 7 , 8 as the sister group of pterobranchs. Recent molecular phylogenies suggest that enteropneusts are probably basal within hemichordates, contrary to previous views^ 9 , but otherwise provide little guidance as to the nature of the primitive hemichordate^ 7 , 8 . In addition, the hemichordate fossil record is almost entirely restricted to peridermal skeletons of pterobranchs, notably graptolites^ 10 , 11 . Owing to their low preservational potentials, fossil enteropneusts are exceedingly rare^ 12 , 13 , 14 , 15 , and throw no light on either hemichordate phylogeny or the proposed harrimaniid–pterobranch transition. Here we describe an enteropneust, Spartobranchus tenuis (Walcott, 1911), from the Middle Cambrian-Period (Series 3, Stage 5) Burgess Shale. It is remarkably similar to the extant harrimaniids, but differs from all known enteropneusts in that it is associated with a fibrous tube that is sometimes branched. We suggest that this is the precursor of the pterobranch periderm, and supports the hypothesis that pterobranchs are miniaturized and derived from an enteropneust-like worm^ 5 , 6 . It also shows that the periderm was acquired before size reduction and acquisition of feeding tentacles, and that coloniality emerged through aggregation of individuals, perhaps similar to the Cambrian rhabdopleurid Fasciculitubus ^ 11 . The presence of both enteropneusts and pterobranchs in Middle Cambrian strata, suggests that hemichordates originated at the onset of the Cambrian explosion. Enteropneusts, or acorn worms, are mud-dwelling creatures that live from the foreshore down to the deep ocean. They are related to pterobranchs, small, colonial, tube-dwelling animals that superficially look completely different. Both are related to echinoderms (starfish and allies) and chordates — the group of animals that includes ourselves. Here Jean-Bernard Caron and colleagues describe fossil enteropneusts from the famous Cambrian Burgess Shale of British Columbia. They look much like some modern enteropneusts, but lived in tubes, more like modern pterobranchs. This adds to the diversity of the fossil fauna and gives pointers to what the common ancestor of enteropneusts and pterobranchs looked like. It might also fuel the debate about whether the ancestor of chordates was a free-living worm, or a sessile, colonial creature.
Simon Conway Morris - One of the best experts on this subject based on the ideXlab platform.
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Tubicolous enteropneusts from the Cambrian Period
Nature, 2013Co-Authors: Jean-bernard Caron, Simon Conway Morris, Christopher B. CameronAbstract:Examination of a fossil enteropneust, Spartobranchus tenuis (Walcott, 1911), from the Cambrian-Period Burgess Shale shows that they looked similar to modern enteropneusts but lived in tubes, like modern pterobranchs; the findings shed light on the common ancestor of enteropneusts and pterobranchs, and hence the origin of chordates. Hemichordates are a marine group that, apart from one monospecific pelagic larval form, are represented by the vermiform enteropneusts and minute colonial tube-dwelling pterobranchs. Together with echinoderms, they comprise the clade Ambulacraria^ 1 . Despite their restricted diversity, hemichordates provide important insights into early deuterostome evolution, notably because of their pharyngeal gill slits^ 2 . Hemichordate phylogeny has long remained problematic^ 3 , 4 , not least because the nature of any transitional form that might serve to link the anatomically disparate enteropneusts and pterobranchs is conjectural. Hence, inter-relationships have also remained controversial. For example, pterobranchs have sometimes been compared to ancestral echinoderms^ 1 . Molecular data identify enteropneusts as paraphyletic, and harrimaniids^ 5 , 6 , 7 , 8 as the sister group of pterobranchs. Recent molecular phylogenies suggest that enteropneusts are probably basal within hemichordates, contrary to previous views^ 9 , but otherwise provide little guidance as to the nature of the primitive hemichordate^ 7 , 8 . In addition, the hemichordate fossil record is almost entirely restricted to peridermal skeletons of pterobranchs, notably graptolites^ 10 , 11 . Owing to their low preservational potentials, fossil enteropneusts are exceedingly rare^ 12 , 13 , 14 , 15 , and throw no light on either hemichordate phylogeny or the proposed harrimaniid–pterobranch transition. Here we describe an enteropneust, Spartobranchus tenuis (Walcott, 1911), from the Middle Cambrian-Period (Series 3, Stage 5) Burgess Shale. It is remarkably similar to the extant harrimaniids, but differs from all known enteropneusts in that it is associated with a fibrous tube that is sometimes branched. We suggest that this is the precursor of the pterobranch periderm, and supports the hypothesis that pterobranchs are miniaturized and derived from an enteropneust-like worm^ 5 , 6 . It also shows that the periderm was acquired before size reduction and acquisition of feeding tentacles, and that coloniality emerged through aggregation of individuals, perhaps similar to the Cambrian rhabdopleurid Fasciculitubus ^ 11 . The presence of both enteropneusts and pterobranchs in Middle Cambrian strata, suggests that hemichordates originated at the onset of the Cambrian explosion. Enteropneusts, or acorn worms, are mud-dwelling creatures that live from the foreshore down to the deep ocean. They are related to pterobranchs, small, colonial, tube-dwelling animals that superficially look completely different. Both are related to echinoderms (starfish and allies) and chordates — the group of animals that includes ourselves. Here Jean-Bernard Caron and colleagues describe fossil enteropneusts from the famous Cambrian Burgess Shale of British Columbia. They look much like some modern enteropneusts, but lived in tubes, more like modern pterobranchs. This adds to the diversity of the fossil fauna and gives pointers to what the common ancestor of enteropneusts and pterobranchs looked like. It might also fuel the debate about whether the ancestor of chordates was a free-living worm, or a sessile, colonial creature.
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The Cambrian "explosion": slow-fuse or megatonnage?
Proceedings of the National Academy of Sciences of the United States of America, 2000Co-Authors: Simon Conway MorrisAbstract:Clearly, the fossil record from the Cambrian Period is an invaluable tool for deciphering animal evolution. Less clear, however, is how to integrate the paleontological information with molecular phylogeny and developmental biology data. Equally challenging is answering why the Cambrian Period provided such a rich interval for the redeployment of genes that led to more complex bodyplans.
Haiyan Li - One of the best experts on this subject based on the ideXlab platform.
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cyclostratigraphy of the global stratotype section and point gssp of the basal guzhangian stage of the Cambrian Period
Palaeogeography Palaeoclimatology Palaeoecology, 2020Co-Authors: Jichuang Fang, Huaichun Wu, Qiang Fang, Shihong Zhang, Tianshui Yang, Haiyan LiAbstract:Abstract The Cambrian is the first Period of the Phanerozoic during which numerous major geological and biological events occurred. Understanding these events requires a high-resolution time scale. The Luoyixi section in Guzhang (Hunan Province, China) is the global stratotype section and point (GSSP) for the Guzhangian Stage. Here, magnetic susceptibility and δ13C data were used to conduct cyclostratigraphic analyses covering the upper Drumian through lower Guzhangian stages. The results of the power spectral analyses and average spectral misfit analyses indicate that the 25–25.53 m, 6.25–6.91 m, 1.90–2.03 m, and 1.08–1.19 m sedimentary cycles may represent long-eccentricity, short-eccentricity, obliquity and precession cycles, respectively. A ~1400 kyr floating astronomical time scale was constructed using the stable 405-kyr eccentricity cycles to calibrate the agnostoid trilobite zones. The obtained fundamental obliquity Period (30.7 ± 0.7 kyr) implies 370,180 ± 1220 km (vs. 384,000 km for present day) for the Earth–Moon distance and 21.58 ± 0.18 h (vs. 23.93 h for present day) for the length of day during the middle Cambrian (500 Ma).
Jianbo Liu - One of the best experts on this subject based on the ideXlab platform.
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Fossil embryos from the Middle and Late Cambrian Period of Hunan, south China.
Nature, 2004Co-Authors: Xi-ping Dong, Philip C. J. Donoghue, Hong Cheng, Jianbo LiuAbstract:Comparative embryology is integral to uncovering the pattern and process of metazoan phylogeny1, but it relies on the assumption that life histories of living taxa are representative of their antecedents. Fossil embryos provide a crucial test of this assumption and, potentially, insight into the evolution of development, but because discoveries so far2,3,4,5 lack phylogenetic constraint, their significance is moot. Here we describe a collection of embryos from the Middle and Late Cambrian Period (500 million years ago) of Hunan, south China, that preserves stages of development from cleavage to the pre-hatching embryo of a direct-developing animal comparable to living Scalidophora (phyla Priapulida, Kinorhyncha, Loricifera). The latest-stage embryos show affinity to the Lower Cambrian embryo Markuelia3, whose life-history strategy contrasts both with the primitive condition inferred for metazoan phyla and with many proposed hypotheses of affinity3,6, all of which prescribe indirect development. Phylogenetic tests based on these embryological data suggest a stem Scalidophora affinity. These discoveries corroborate, rather than contradict, the predictions of comparative embryology, providing direct historical support for the view that the life-history strategies of living taxa are representative of their stem lineages.
