Paul A. Selden

Functional morphology of the prosoma of Baltoeurypterus tetragonophthalmus (Fischer) (Chelicerata: Eurypterida)

The prosomal morphology of Baltoeurypterus tetragonophthalmus (Fischer) from the Baltic Silurian is redescribed and reconstructed. The first eurypterid labrum and new secondary sexual characters of Baltoeurypterus are described. The radially-arranged coxae of Baltoeurypterus were capable of adduction and abduction for food mastication, but not promotor-remotor movements for locomotion. Joint diagrams are presented for the first time for an extinct arthropod. Promotion and remotion of the limbs occurred about subvertical trochanteral pivots, as in all other chelicerates except xiphosurans. Baltoeurypterus probably walked in a “slow” gait; a method of choosing possible gaits for extinct arthropods is outlined. Swimming in Baltoeurypterus was effected by means of a rowing action of the posterior limb pair, which is provided with complex joints for collapsing the paddle during the recovery stroke. The limb arrangement and joint mechanisms of Baltoeurypterus are intermediate between those of the xiphosurans and the arachnids. It is possible that a sister relationship exists between the eurypterids and some arachnid groups, which would render Merostomata and Arachnida unnatural assemblages.

Palaeophysiology of terrestrialisation in the Chelicerata

The wide range of organs of respiration (book-gills, book-lungs, sieve- and tube-tracheae), reproduction, sensory perception, etc., among the chelicerates indicates that the major groups made the transition to land life independently. The fossil record is patchy for most chelicerate groups, certain intervals (e.g. Westphalian) being particularly rich in chelicerate bearing Lagerstatten while in others (e.g. Mesozoic) they are sparse. Due, apparently, to their unusual hyaline exocuticle, scorpions are better preserved than other arthropods, and show a fairly continuous record from fully aquatic forms in the Silurian, to both aquatic and terrestrial faunas in the Carboniferous. In particular, new and well-preserved material of the earliest demonstrably terrestrial scorpions from the Lower Carboniferous of East Kirkton, West Lothian, suggests that book-lungs, at least in the scorpions, developed directly from book-gills by suturing of the covering plate (Blattfuss of the related eurypterids) to leave stigmata for diffusion of air. This evidence supports the ideas of early authors that the scorpion mesosomal ‘sternites’ are fused plates, contra Kjellesvig-Waering (1986) who envisaged the plates being lost to reveal true sternites beneath. The fossil evidence also indicates that by the Triassic at least two scorpion lineages had evolved intra-‘sternite’ stigmata.

RESISTANCE OF SPIDERS TO CRETACEOUS–TERTIARY EXTINCTION EVENTS

Abstract Throughout Earth history a small number of global catastrophic events leading to biotic crises have caused mass extinctions. Here, using a technique that combines taxonomic and numerical data, we consider the effects of the Cenomanian—Turonian and Cretaceous—Tertiary mass extinctions on the terrestrial spider fauna in the light of new fossil data. We provide the first evidence that spiders suffered no decline at the family level during these mass extinction events. On the contrary, we show that they increased in relative numbers through the Cretaceous and beyond the Cretaceous—Tertiary extinction event.

The true identity of the supposed giant fossil spider Megarachne

Megarachne servinei from the Permo-Carboniferous Bajo de Véliz Formation of San Luis Province, Argentina (32° 17′ S, 65° 25′ E), was described as a giant mygalomorph spider (‘tarantula’) and, with its body length of 339 mm, the largest known spider ever to have lived on Earth. Its identification as a spider was based on interpretations of the shape of the carapace, the position of the eye tubercle, the anterior protrusion of the carapace as a pair of chelicerae, and the posterior circular structure as the abdomen. X-radiography revealed possible morphology hidden in the matrix: cheliceral fangs, sternum, labium and coxae, and so a reconstruction of Megarachne as a giant spider was presented. Difficulties with the interpretation (unusual cuticular ornament, suture dividing the carapace and spade-like anterior border of the chelicera), together with non-preservation of synapomorphies of Araneae, provoked debate about its interpretation as a spider. Now, the holotype and a new specimen have become available for study. Megarachne is shown to be a bizarre eurypterid (‘sea-scorpion’), similar to rare forms known from Carboniferous rocks of Scotland and South Africa, and is the most complete eurypterid so far recorded from Carboniferous strata of South America.

Eurypterids from the Viséan of East Kirkton, West Lothian, Scotland

The hibbertopteroid eurypterid genera Hibbertopterus, Dunsopterus, and Cyrtoctenus occur in the East Kirkton Limestone of Bathgate, West Lothian. Most specimens are fragmentary and appear to have been washed into the depositional area with plant debris and tuffaceous sediment. Nearly all of the identifiable material can be attributed to Hibbertopterus scouleri (Hibbert), but two isolated Cyrtoctenus combs, and a femur comparable with Dunsopterus have also been recognised. New material of Hibbertopterus scouleri (Hibbert) reveals that the posterior legs and telson resemble those of the cyrtoctenids more closely than was previously thought. It is possible that Hibbertopterus, Dunsopterus, and Cyrtoctenus are indistinguishable except by relatively minor characteristics, and that all of the material from East Kirkton Quarry might be derived from a single eurypterid species

A New Carcinosomatid Eurypterid From The Upper Silurian Of Northern Vietnam

Fearnsides Fund of the Geological Society, NERC grant GT4/92/226/G, and Leverhulme Trust grant F/82/AZ

MISSING LINKS BETWEEN ARGYRONETA AND CYBAEIDAE REVEALED BY FOSSIL SPIDERS

Abstract Argyroneta aquatica (Clerck 1757) should be included in Cybaeidae Simon 1898. There is no justification for a monotypic family Argyronetidae; differences from other cybaeids are either specializations for aquatic life or derived with respect to other cybaeids. The features of a recently described Eocene spider, Vectaraneus yulei Selden 2001 are discussed, which place it together with Argyroneta in subfamily Argyronetinae Thorell 1870 of Cybaeidae. Fossil spiders intermediate between Vectaraneus and Argyroneta are reviewed.

New morphological and host data for the ectoparasitic larva of Leptus hidakai Kawashima (Acari, Acariformes, Erythraeidae)

The larva of Leptus hidakai Kawashima is redescribed. This species, previously only known from its type-locality in Japan, is recorded for the first time from the uloborid spider Miagrammopes singaporensis Kulczynski in Singapore. Records of Leptus larvae infesting Arachnida are listed.

Der Rhynie Chert, Unter-Devon, Schottland

Die verkieselten Ablagerungen von Rhynie, der sogenannte „Rhynie Chert“, mit seinen vorzuglich erhaltenen Pflanzen und Arthropoden, wurden von Dr. W. Mackie 1912 als Steine in Mauern und als lose Blocke auf Feldern entdeckt, als er das Gebiet um Ord Hill kartierte (Mackie 1913). Der erste Bericht uber den Rhynie Chert wurde in Home et al. (1916) publiziert, nachdem D. Trait durch Grabungen das von jungeren Ablagerungen uberdeckte Vorkommen lokalisieren konnte. Die klassischen Arbeiten von Kidston et Lang (1917, 1920 a, b, 1921 a, b) basieren auf Material aus Traits Schurfen. Diesen Arbeiten sind bis heute zahlreiche Untersuchungen gefolgt, die auf Material aus weiteren Schurfen, in jungerer Zeit auch aus Bohrungen, beruhen.