Head Structure in Upper Stem‐group Euarthropods

Budd, Graham E.

doi:10.1111/j.1475-4983.2008.00752.x

Cited by 59 publications

(74 citation statements)

References 24 publications

(72 reference statements)

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“…Reconstructions of organ systems made using Adobe Illustrator are based on specimens preserving the gut (YKLP 11336, YKLP 11337, YKLP 11338 and YKLP 11339), the brain (YKLP 15006 (ref. 8)), segmental nervous system 14 and vascular system (YKLP 11335) with references to described external morphology [1][2][3][4][5][6] .…”

Section: Methodsmentioning

confidence: 99%

“…Its placement crownwards of anomalocaridids and bivalved arthropods such as Canadaspis refers especially to its head tagmosis and appendicular structures [1][2][3][4][5][6] and this phylogenetic position has been retrieved in comprehensive cladistic analyses 7 . Documentation of its brain and optic neuropils rather unexpectedly introduced similarities to crown-group euarthropods 8 , in particular to members of the Mandibulata.…”

mentioning

confidence: 99%

“…The exoskeletal and appendicular morphologies of F. protensa have been studied in detail, and this taxon remains the Cambrian arthropod with the most detailed information on the brain and its connections to segmental structures in the head 6,8 . Various specimens also reveal anatomical details of the gut [4][5][6] .…”

mentioning

confidence: 99%

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An exceptionally preserved arthropod cardiovascular system from the early Cambrian

Peng

Hou

et al. 2014

Nat Commun

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The assumption that amongst internal organs of early arthropods only the digestive system withstands fossilization is challenged by the identification of brain and ganglia in early Cambrian fuxianhuiids and megacheirans from southwest China. Here we document in the 520-million-year-old Chengjiang arthropod Fuxianhuia protensa an exceptionally preserved bilaterally symmetrical organ system corresponding to the vascular system of extant arthropods. Preserved primarily as carbon, this system includes a broad dorsal vessel extending through the thorax to the brain where anastomosing branches overlap brain segments and supply the eyes and antennae. The dorsal vessel provides segmentally paired branches to lateral vessels, an arthropod ground pattern character, and extends into the anterior part of the abdomen. The addition of its vascular system to documented digestive and nervous systems resolves the internal organization of F. protensa as the most completely understood of any Cambrian arthropod, emphasizing complexity that had evolved by the early Cambrian.

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Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 99%

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An exceptionally preserved arthropod cardiovascular system from the early Cambrian

Peng

Hou

et al. 2014

Nat Commun

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“…Cambrian arthropods have sometimes been "shoehorned" into modern clades, despite having character combinations that support deeper, more stem-ward phylogenetic positions (7,46). Conversely, the Deadwood fossils risk being assigned to inappropriately derived positions because of their "modern" appearance but disarticulated condition.…”

Section: Discussionmentioning

confidence: 99%

Exceptionally preserved crustaceans from western Canada reveal a cryptic Cambrian radiation

Harvey

Vélez

Butterfield

2012

Proc. Natl. Acad. Sci. U.S.A.

112

101

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The early history of crustaceans is obscured by strong biases in fossil preservation, but a previously overlooked taphonomic mode yields important complementary insights. Here we describe diverse crustacean appendages of Middle and Late Cambrian age from shallow-marine mudstones of the Deadwood Formation in western Canada. The fossils occur as flattened and fragmentary carbonaceous cuticles but provide a suite of phylogenetic and ecological data by virtue of their detailed preservation. In addition to an unprecedented range of complex, largely articulated filtering limbs, we identify at least four distinct types of mandible. Together, these fossils provide the earliest evidence for crown-group branchiopods and total-group copepods and ostracods, extending the respective ranges of these clades back from the Devonian, Pennsylvanian, and Ordovician. Detailed similarities with living forms demonstrate the early origins and subsequent conservation of various complex food-handling adaptations, including a directional mandibular asymmetry that has persisted through half a billion years of evolution. At the same time, the Deadwood fossils indicate profound secular changes in crustacean ecology in terms of body size and environmental distribution. The earliest radiation of crustaceans is largely cryptic in the fossil record, but “small carbonaceous fossils” reveal organisms of surprisingly modern aspect operating in an unfamiliar biosphere.

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“…Compelling candidates also represent the upper part of the stem group, more closely related to extant arthropods. The systematic position of Fuxianhuiida, an early Cambrian group from China, in the arthropod stem group has received broad consensus (Chen et al 1995;Hou and Bergström 1997;Budd 2002Budd , 2008Hou 1998, 2005;Waloszek et al 2005Waloszek et al , 2007, despite varying interpretations of head structures. The following discussion focuses on how these fossils inform on the sequence of character acquisition in the arthropod head and trunk limbs.…”

Section: Character Evolution In the Arthropod Stem Group: An Examplementioning

confidence: 99%

Palaeontological and Molecular Evidence Linking Arthropods, Onychophorans, and other Ecdysozoa

Edgecombe

2009

Evo Edu Outreach

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Membership of Arthropoda in a clade of molting animals, the Ecdysozoa, has received a growing body of support over the past 10 years from analyses of DNA sequences from many genes together with morphological characters involving the cuticle and its molting. Recent analyses based on broad phylogenomic sampling strengthen the grouping of cycloneuralian worms and arthropods as Ecdysozoa, identify the velvet worms (Phylum Onychophora) as the closest living relatives of arthropods, and interpret segmentation as having separate evolutionary origins in arthropods and annelid worms. Determining whether the water bears (Phylum Tardigrada) are more closely related to onychophorans and arthropods or to unsegmented cycloneuralians such as roundworms (Nematoda) is an open question. Fossil taxa such as the Cambrian anomalocaridids provide a combination of arthropod and cycloneuralian characters that is not observed in any living ecdysozoan. Fossils break up long branches and help to resolve the sequence of character acquisition at several critical nodes in the arthropod tree, notably in a suite of Cambrian lobopodians that may include the stem groups of each of the major panarthropod lineages.

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Head Structure in Upper Stem‐group Euarthropods

Cited by 59 publications

References 24 publications

An exceptionally preserved arthropod cardiovascular system from the early Cambrian

An exceptionally preserved arthropod cardiovascular system from the early Cambrian

Exceptionally preserved crustaceans from western Canada reveal a cryptic Cambrian radiation

Palaeontological and Molecular Evidence Linking Arthropods, Onychophorans, and other Ecdysozoa

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