Phalangiotarbid arachnids from the Coal Measures of Lancashire, UK

Dunlop, Jason A.; Horrocks, Carl A.

doi:10.1017/s0016756897007073

Cited by 11 publications

(31 citation statements)

References 9 publications

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“…2B ). Some previous studies have noted possible openings for (?tracheal) spiracles among the anteriormost sternites ( Dunlop & Horrocks, 1997 , Fig. 2), but these could not be identified unequivocally here.…”

Section: Tomography Resultsmentioning

confidence: 81%

Three-dimensional reconstruction and the phylogeny of extinct chelicerate orders

Garwood

Dunlop

2014

PeerJ

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Arachnids are an important group of arthropods. They are: diverse and abundant; a major constituent of many terrestrial ecosystems; and possess a deep and extensive fossil record. In recent years a number of exceptionally preserved arachnid fossils have been investigated using tomography and associated techniques, providing valuable insights into their morphology. Here we use X-ray microtomography to reconstruct members of two extinct arachnid orders. In the Haptopoda, we demonstrate the presence of ‘clasp-knife’ chelicerae, and our novel redescription of a member of the Phalangiotarbida highlights leg details, but fails to resolve chelicerae in the group due to their small size. As a result of these reconstructions, tomographic studies of three-dimensionally preserved fossils now exist for three of the four extinct orders, and for fossil representatives of several extant ones. Such studies constitute a valuable source of high fidelity data for constructing phylogenies. To illustrate this, here we present a cladistic analysis of the chelicerates to accompany these reconstructions. This is based on a previously published matrix, expanded to include fossil taxa and relevant characters, and allows us to: cladistically place the extinct arachnid orders; explicitly test some earlier hypotheses from the literature; and demonstrate that the addition of fossils to phylogenetic analyses can have broad implications. Phylogenies based on chelicerate morphology—in contrast to molecular studies—have achieved elements of consensus in recent years. Our work suggests that these results are not robust to the addition of novel characters or fossil taxa. Hypotheses surrounding chelicerate phylogeny remain in a state of flux.

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Section: Tomography Resultsmentioning

confidence: 81%

Three-dimensional reconstruction and the phylogeny of extinct chelicerate orders

Garwood

Dunlop

2014

PeerJ

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“…In the decades since these contributions, Geological Magazine has continued to publish a range of works on early land ecosystems and related topics. Examples include: Palaeozoic palaeobotanical papers such Silurian macroscopic plants (Edwards & Rogerson, 1979), Silurian-Devonian biostratigraphy within the Anglo-Welsh Basin (Wellman et al 1998), British coal measures flora (Cleal, 1986), and Devonian lycopsids in Argentina (Cingolani et al 2002), China (Xu & Wang, 2008) and Colombia (Berry et al 2000); palynology studies with implications for the timing of terrestrialization in multiple groups (Marshall, 1991) and Silurian biostratigraphy (Gray et al 1992); Ordovician traces potentially recording terrestrial animals (Johnson et al 1994) and Early Devonian traces recording myriapods or relatives (Smith et al 2003); Palaeozoic terrestrial arthropods including arachnids (Dunlop & Horrocks, 1997) and insects (Jarzembowski & Schneider, 2007); a new arthropod fauna from the Westhoughton open-cast coal pit (Anderson et al 1999); and topics in Palaeozoic correlation (Rickards, 2000;Cocks et al 2010).…”

Section: Geological Magazine and Terrestrializationmentioning

confidence: 99%

An introduction to the Rhynie chert

Garwood

Oliver²,

Spencer

2019

Geol. Mag.

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The terrestrialization of life has profoundly affected the biosphere, geosphere and atmosphere, and the Geological Magazine has published key works charting the development of our understanding of this process. Integral to this understanding – and featuring in one of the Geological Magazine publications – is the Devonian Rhynie chert Konservat-Lagerstätte located in Aberdeenshire, Scotland. Here we provide a review of the work on this important early terrestrial deposit to date. We begin by highlighting contributions of note in the Geological Magazine improving understanding of terrestrialization and Palaeozoic terrestrial ecosystems. We then introduce the Rhynie chert. The review highlights its geological setting: the Caledonian context of the Rhynie Basin and its nature at the time of deposition of the cherts which host its famous fossils. There follows an introduction to the development of the half-graben in which the cherts and host sediments were deposited, the palaeoenvironment this represented and the taphonomy of the fossils themselves. We subsequently provide an overview of the mineralization and geochemistry of the deposit, and then the fossils found within the Rhynie chert. These include: six plant genera, which continue to provide significant insights into the evolution of life on land; a range of different fungi, with recent work starting to probe plant–fungus interactions; lichens, amoebae and a range of unicellular eukaryotes and prokaryotes (algae and cyanobacteria); and finally a range of both aquatic and terrestrial arthropods. Through continued study coupled with methodological advances, Rhynie fossils will continue to provide unique insights into early life on land.

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“…They have been likened either to harvestmen or opilioacarid mites, but a recent attempt to resolve their phylogenetic position (Garwood and Dunlop, 2014a) was unable to recover a robust position for this group as a number of key characters, such as the nature of the mouthparts, remain equivocal. Accounts of their external morphology can be found in, e.g., Dunlop and Horrocks (1997) and Pollitt et al (2004). Phalangiotarbids (Fig.…”

Section: Phalangiotarbida Ymentioning

confidence: 99%

“…Somites XIIIeXV in phalangiotarbids were either covered dorsally by three large tergites, or in some taxa these three elements have fused together into a single shield. Ventrally the anterior opisthosomal sternites are similarly short and concentrated like the anterior tergites and there is some evidence for two pairs of spiracles, perhaps opening on somites X and XI (Dunlop and Horrocks, 1997 : Fig. 6).…”

Section: Phalangiotarbida Ymentioning

confidence: 99%