Palaeoisopus, Palaeopantopus andPalaeothea, pycnogonid arthropods from the Lower Devonian Hunsriick Slate, West Germany

Bergström, Johan; Stürmer, Wilhelm; Winter, George

doi:10.1007/bf02985882

Cited by 74 publications

(81 citation statements)

References 12 publications

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“…l . ; problematic because the proximal rings in Palaeoisopus problematicus could be homologous to the partially sclerotized half-rings [96]); 31, dorsal median eyes; 35, hypostomal sclerite absent. Further characters that are present in Euchelicerata and have been optimized for Chelicerata: 56, apodous abdomen (possibly with Pycnogonida, see Palaeoisopus ; convergent with Yohoia , Martinssonia + Eucrustacea, and Sidneyia ); 66, keeled styliform telson (present in Palaeoisopus ).…”

Section: Resultsmentioning

confidence: 99%

Arthroaspis n. gen., a common element of the Sirius Passet Lagerstätte (Cambrian, North Greenland), sheds light on trilobite ancestry

et al. 2013

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BackgroundExceptionally preserved Palaeozoic faunas have yielded a plethora of trilobite-like arthropods, often referred to as lamellipedians. Among these, Artiopoda is supposed to contain taxa united by a distinctive appendage structure. This includes several well supported groups, Helmetiida, Nektaspida, and Trilobita, as well as a number of problematic taxa. Interrelationships remain unclear, and the position of the lamellipedian arthropods as a whole also remains the subject of debate.ResultsArthroaspis bergstroemi n. gen. n. sp., a new arthropod from the early Cambrian Sirius Passet Lagerstätte of North Greenland shows a striking combination of both dorsal and ventral characters of Helmetiida, Nektaspida, and Trilobita. Cladistic analysis with a broad taxon sampling of predominantly early Palaeozoic arthropods yields a monophyletic Lamellipedia as sister taxon to the Crustacea or Tetraconata. Artiopoda is resolved as paraphyletic, giving rise to the Marrellomorpha. Within Lamellipedia, a clade of pygidium bearing taxa is resolved that can be shown to have a broadly helmetiid-like tergite morphology in its ground pattern. This morphology is plesiomorphically retained in Helmetiida and in Arthroaspis, which falls basally into a clade containing Trilobita. The trilobite appendages, though similar to those of other lamellipedians in gross morphology, have a unique outward rotation of the anterior trunk appendages, resulting in a ‘hard wired’ lateral splay, different to that observed in other Lamellipedia.ConclusionsThe combination of helmetiid, trilobite, and nektaspid characters in Arthroaspis gives important hints concerning character polarisation within the trilobite-like arthropods. The distinctive tergite morphology of trilobites, with its sophisticated articulating devices, is derived from flanged edge-to-edge articulating tergites forming a shield similar to the helmetiids, previously considered autapomorphic for that group. The stereotypical lateral splay of the appendages of lamellipedians is a homoplastic character shown to be achieved by several groups independently.

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Section: Resultsmentioning

confidence: 99%

Arthroaspis n. gen., a common element of the Sirius Passet Lagerstätte (Cambrian, North Greenland), sheds light on trilobite ancestry

et al. 2013

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“…In addition the technique has been used to locate fossils in the field (Sturmer, 1983) and to study the structure of soft part anatomy in exceptionally preserved faunas such as those of the Devonian Hunsruck Shales (Sturmer, 1970(Sturmer, , 1985Sturmer & Bergstrom, 1973, 1976, 1978, 1981Bergstrom, Sturmer & Winter, 1980). The technique has not previously been modified to examine microvertebrates.…”

Section: Discussionmentioning

confidence: 99%

Studies of tooth implantation in fossil tetrapods using high-resolution X-radiography

Fraser

Shelton

1988

Geol. Mag.

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The concept that reptilian tooth implantations fall neatly into a number of separate categories which can be used in phylogenetic studies is called into question. The use of microfocal Xradiography in preliminary studies of reptilian dentitions reveals that, at least in sphenodontids, there is no clear distinction between acrodonty and pleurodonty. Although the technique is used here specifically in connection with microvertebrates, it may have considerable potential in evaluating internal structures in a wide range of fossils.

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“…Interestingly, given the narrow cephalosoma (anterior tagma) of sea spiders and the loss of the opisthosoma ("abdomen" or posterior tagma), the gonads and other organs are found in their appendages (Cobb 2010 ). However, the fossil record of pycnogonids, which extends to the Cambrian (Waloszek and Dunlop 2002 ), includes an extinct lineage with a long, completely segmented, limbless posterior region, indicating that stem pycnogonids once bore an opisthosoma (Bergström et al 1980 ). Since sea spiders are widely regarded as the sister group to the euchelicerates ( Fig.…”

Section: Pycnogonida (Sea Spiders)mentioning

confidence: 96%

Chelicerata

Schwager

Schönauer

Leite

et al. 2015

Evolutionary Developmental Biology of Invertebrates 3

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Palaeoisopus, Palaeopantopus andPalaeothea, pycnogonid arthropods from the Lower Devonian Hunsriick Slate, West Germany

Cited by 74 publications

References 12 publications

Arthroaspis n. gen., a common element of the Sirius Passet Lagerstätte (Cambrian, North Greenland), sheds light on trilobite ancestry

Arthroaspis n. gen., a common element of the Sirius Passet Lagerstätte (Cambrian, North Greenland), sheds light on trilobite ancestry

Studies of tooth implantation in fossil tetrapods using high-resolution X-radiography

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