Almost a spider: a 305-million-year-old fossil arachnid and spider origins

Spiders are an important animal group, with a long history. Details of their origins remain limited, with little knowledge of their stem group, and no insights into the sequence of character acquisition during spider evolution. We describe a new fossil arachnid, Idmonarachne brasieri gen. et sp. nov. from the Late Carboniferous (Stephanian, ca 305–299 Ma) of Montceau-les-Mines, France. It is three-dimensionally preserved within a siderite concretion, allowing both laboratory- and synchrotron-based phase-contrast computed tomography reconstruction. The latter is a first for siderite-hosted fossils and has allowed us to investigate fine anatomical details. Although distinctly spider-like in habitus, this remarkable fossil lacks a key diagnostic character of Araneae: spinnerets on the underside of the opisthosoma. It also lacks a flagelliform telson found in the recently recognized, spider-related, Devonian–Permian Uraraneida. Cladistic analysis resolves our new fossil as sister group to the spiders: the spider stem-group comprises the uraraneids and I. brasieri. While we are unable to demonstrate the presence of spigots in this fossil, the recovered phylogeny suggests the earliest character to evolve on the spider stem-group is the secretion of silk. This would have been followed by the loss of a flagelliform telson, and then the ability to spin silk using spinnerets. This last innovation defines the true spiders, significantly post-dates the origins of silk, and may be a key to the group's success. The Montceau-les-Mines locality has previously yielded a mesothele spider (with spinnerets). Evidently, Late Palaeozoic spiders lived alongside Palaeozoic arachnid grades which approached the spider condition, but did not express the full suite of crown-group autapomorphies

An ammonia spectral map of the L1495-B218 filaments in the Taurus molecular cloud. I. Physical properties of filaments and dense cores

We present deep NH3 observations of the L1495-B218 filaments in the Taurus molecular cloud covering over a 3° angular range using the K-band focal plane array on the 100 m Green Bank Telescope. The L1495-B218 filaments form an interconnected, nearby, large complex extending over 8 pc. We observed NH3 (1, 1) and (2, 2) with a spectral resolution of 0.038 km s−1 and a spatial resolution of 31''. Most of the ammonia peaks coincide with intensity peaks in dust continuum maps at 350 and 500 μm. We deduced physical properties by fitting a model to the observed spectra. We find gas kinetic temperatures of 8–15 K, velocity dispersions of 0.05–0.25 km s−1, and NH3 column densities of 5 × 1012 to 1 × 1014 cm−2. The CSAR algorithm, which is a hybrid of seeded-watershed and binary dendrogram algorithms, identifies a total of 55 NH3 structures, including 39 leaves and 16 branches. The masses of the NH3 sources range from 0.05 to 9.5 ${{M}_{\odot }}$. The masses of NH3 leaves are mostly smaller than their corresponding virial mass estimated from their internal and gravitational energies, which suggests that these leaves are gravitationally unbound structures. Nine out of 39 NH3 leaves are gravitationally bound, and seven out of nine gravitationally bound NH3 leaves are associated with star formation. We also found that 12 out of 30 gravitationally unbound leaves are pressure confined. Our data suggest that a dense core may form as a pressure-confined structure, evolve to a gravitationally bound core, and undergo collapse to form a protostar

Tomographic reconstruction of the exceptionally preserved trigonotarbid arachnid Eophrynus prestvicii

An exceptionally preserved specimen of the extinct trigonotarbid arachnid Eophrynus prestvicii (Arachnida: Trigonotarbida) from the Late Carboniferous (Duckmantian) British Middle Coal Measures of the UK is redescribed with the help of X-ray micro-tomography (XMT). Previous work is summarised and the correct spelling of the species name confirmed. Reconstruction of the void left by the original specimen within a siderite (ironstone) nodule reveals its three-dimensional structure as well as novel details which are difficult to resolve using traditional methods of study. The pedipalps and legs can now be reconstructed almost in their entirety and we can confirm that the chelicerae hung beneath the prosoma with a backwards-directed fang. Opisthosomal segmentation is clarified: a narrow tergite 1 is followed by eight further tergites (2–9), clearly demarked by their ornamentation. In general, a much more accurate picture of the spines and tuberculation ornamenting the dorsal surface of the body was resolved. Ventrally the opisthosoma bears socalled ventral sacs and terminates in a two-segmented pygidium. Based on the XMT model, a new reconstruction of E. prestvicii is presented. Although phylogenetically unrelated, the sometimes similar-looking, spiny and tuberculate lanitorid harvestmen (Opiliones: Lanitores) offer a possible ecological model for these highly ornamented trigonotarbids

Carboniferous araneomorph spiders reinterpreted as long-bodied harvestmen

<p><i>Archaeometa nephilina</i> Pocock, <a href="#cit0021" target="_blank">1911</a> from the Late Carboniferous (Bashkirian/Moscovian: Duckmantian, <i>c</i>.315 Ma) Coal Measures of Coseley in the English West Midlands was originally interpreted as an araneomorph spider (Arachnida: Araneae). It is, in fact, a harvestman (Arachnida: Opiliones), albeit one with an unusual, long-bodied morphology. Another Coseley fossil, <i>Arachnometa tuberculata</i> Petrunkevitch, <a href="#cit0018" target="_blank">1949</a>, was also interpreted as an araneomorph spider, but it is not well preserved, and is regarded as Opiliones <i>incertae sedis</i>. Interestingly, the <i>Archaeometa</i> Pocock, <a href="#cit0021" target="_blank">1911</a> body plan, here also revealed through computed microtomography (µCT), has morphological parallels with some modern laniatorid harvestmen in the family Assammidae. However, the Coal Measures fossils do not preserve unequivocal laniatorid apomorphies, and so are referred to an uncertain position within Phalangida (transferred herein from Araneae). The <i>Archaeometa</i> specimens are further examples of Carboniferous Opiliones, which were originally misidentified, and contribute to a picture of an increasingly diverse Coal Measures harvestman fauna.</p> <p><a href="http://zoobank.org/urn:lsid:zoobank.org:pub:E7951158-75F3-46AF-87FB-AE10AD50D94E" target="_blank">http://zoobank.org/urn:lsid:zoobank.org:pub:E7951158-75F3-46AF-87FB-AE10AD50D94E</a></p

High-fidelity X-ray micro-tomography reconstruction of siderite-hosted Carboniferous arachnids

A new approach to maximize data recovery from siderite-hosted fossils is presented. Late Carboniferous trigonotarbids (Arachnida: Trigonotarbida) from Coseley, UK, were chosen to assess the potential of high-resolution X-ray micro-tomography (XMT). Three-dimensional computer reconstruction visualizes the animals at 20 µm or better resolution, resolving subtle and previously unseen details. Novel data recovered includes (possibly plesiomorphic) retention of endites on leg coxae of Cryptomartus hindi (Anthracomartidae) and highlights further similarities between this family and the Devonian Palaeocharinidae. Also revealed is a flattened body with robust anterior limbs, implying a hunting stance similar to modern crab spiders (Thomisidae). Eophrynus prestvicii (Eophrynidae) had more gracile limbs but a heavily ornamented body, with newly identified upward-pointing marginal spines on the opisthosoma. Its habitus is comparable with certain modern laniatorid harvestmen (Opiliones). These findings demonstrate the potential of XMT to revolutionize the study of siderite-hosted Coal Measures fossils

The phylogeny of fossil whip spiders

<p>Additional files for the publication The phylogeny of fossil whip spiders, published in BMC Evolutionary Biology. </p> <p>Additional file 1.  File format: .vaxml (see [38]). Title: Tomographic reconstruction of <em> Graeophonus anglicus</em> Pocock, 1911. Description: A 3D mesh model of Graeophonus anglicus in the VAXML interchange format. </p> <p>Additional file 2.  File format: .pdf. Title: Character statements. Description: Morphological characters statements for the characters used in the current analysis. </p> <p>Additional file 3.  File format: .tnt (see [45]). Title: Cladistic matrix. Description: Cladistic matrix used in the current analysis, in a TNT ready format. </p> <p>Additional file 4. A video showing the tomographic reconstruction of<em> Graeophonus anglicus </em>Pocock, 1911 presented herein; inferred/reconstructed anatomy partially transparent.</p