Lyall I. Anderson

A harvestman (Arachnida: Opiliones) from the Early Devonian Rhynie cherts, Aberdeenshire, Scotland

A harvestman (Arachnida: Opiliones) is described from the Early Devonian (Pragian) Rhynie cherts, Aberdeenshire, Scotland. Eophalangium sheari gen. et sp. nov. is the oldest known harvestman. The material includes both males and a female preserving, respectively, a cuticle-lined penis and ovipositor within the opisthosoma. Both these structures are of essentially modern appearance. The Rhynie fossils also show tracheae which are, again, very similar to those of living harvestmen. This is the oldest unequivocal record of arachnid tracheal respiration and indicates that E. sheari was terrestrial. An annulate, setose ovipositor in the female suggests that it can be excluded from the clades Dyspnoi and Laniatores, in which the ovipositor lacks such annulations. However, the penis shows evidence of two muscles, a feature of uncertain polarity seen in modern Troguloidea (Dyspnoi). The presence of median eyes and long legs excludes Cyphophthalmi, and thus, E. sheari is tentatively referred to the suborder Eupnoi. Therefore, this remarkable material is implicitly a crown-group harvestman and is one of the oldest known crown-group chelicerates. It also suggests an extraordinary degree of morphological stasis within the eupnoid line, with the Devonian forms differing little in gross morphology – and perhaps in reproductive behaviour – from their modern counterp

How many species of fossil arachnids are there

Abstract The species-level diversity of fossil Chelicerata is summarized for each order. 1952 valid species of fossil chelicerates are currently recognized, of which 1593 are arachnids. In order of abundance they are: Araneae (979 fossil species), Actinotrichida (283), Eurypterida (241), Scorpiones (111), Xiphosura (96), Trigonotarbida (71), Pseudoscorpiones (38), Phalangiotarbida (30), Opiliones (25), Ricinulei (15), and Anactinotrichida (11). Other groups are represented by ten fossil species or fewer. Based on published descriptions, spiders thus appear to dominate the fossil arachnid species assemblage, making up a greater proportion of paleodiversity than their Recent diversity would predict. Scorpions are also overrepresented, particularly in the Paleozoic, compared to their modern diversity. By contrast, groups like mites, harvestmen, pseudoscorpions and solifuges are noticeably under-represented as fossils when compared to modern patterns of diversity.

A redescription of Chasmataspis laurencii Caster & Brooks, 1956 (Chelicerata: Chasmataspidida) from the Middle Ordovician of Tennessee, USA, with remarks on chasmataspid phylogeny

The type material of Chasmataspis laurencii Caster & Brooks, 1956 (Chelicerata: Chasmataspidida) from the Middle Ordovician (Tremadoc to Caradoc) of Sevier County, Tennessee, USA, is redescribed, and comparisons are drawn with recently discovered Devonian chasmataspids from Scotland, Germany and Russia. The depositional setting of the C. laurencii fossils is reinterpreted as an ash fall into shallow marine/tidal sediments. Chasmataspis laurencii confirms the presence of 13 opisthosomal segments in Chasmataspidida, a character of unresolved polarity. The phylogenetic position of C. laurencii is difficult to resolve. A monophyletic Chasmataspidida has one convincing autapomorphy in the nine-segmented postabdomen, but C. laurencii shares a number of characters with xiphosurans (i.e. cardiac lobe, pre-abdomen with axial region, biramous and chelate limbs), while the Devonian taxa more closely resemble eurypterids (i.e. through pediform limbs and a genital appendage). Earlier interpretations of the respiratory system in C. laurencii appear unconvincing in the light of new evidence from Devonian forms with opisthosomal opercula. Resting impressions of a Chasmataspis -like animal from the Upper Cambrian Hickory Sandstone of Texas, USA, also appear to show evidence of opercula. These Texan fossils could represent the oldest record of Euchelicerata. Two chasmataspid families are recognised, and C. laurencii is placed in the monotypic Chasmataspididae Caster & Brooks, 1956, redefined here on the fused pre-abdominal buckler with an axial region and the narrow, elongate post-abdomen ending in a long, lanceolate telson.

Xiphosurans from the Westphalian D of the Radstock Basin, Somerset Coalfield, the South Wales Coalfield and Mazon Creek, Illinois

Euproops kilmersdonensis Ambrose & Romano, 1972 is proposed as a synonym of Euproops danae ( Meek & Worthen, 1865 ) from Mazon Creek, Illinois. Five other species attributed to Euproops Meek, 1867 and one species attributed to Prestwichianella nitida Dix & Pringle, 1929 , from the Westphalian D of the South Wales Coalfield, described by Dix & Pringle (1929, 1930) are also synonymized with E. danae . In addition, six species described by Raymond (1944) from Mazon Creek are synonymized with E. danae . The taphonomic processes acting upon xiphosuran body fossils produce spurious morphological differences between specimens, which have been used in the past to define species. It is concluded that species diversity within the Carboniferous Xiphosura was low, contrary to previous reports ( Fisher, 1984 ). The mode of life of E. danae is re-evaluated in the light of trace fossils recently described by Pollard & Hardy (1991) from Writhlington Geological Nature Reserve, and from palaeophysiological considerations.

CHELICERATE ARTHROPODS, INCLUDING THE OLDEST PHALANGIOTARBID ARACHNID, FROM THE EARLY DEVONIAN (SIEGENIAN) OF THE RHENISH MASSIF, GERMANY

Abstract A relatively diverse chelicerate fauna has been detected in Early Devonian, Siegenian strata of the Westerwald area, Rhineland-Palatinate, Germany. The arachnids, comprising trigonotarbids and the oldest phalangiotarbids, are described and figured here along with the chasmataspidids. To accomodate the phalangiotarbid a new genus and species in the family Architarbidae, Devonotarbus hombachensis, is raised. Devonotarbus n. gen. is characterized by an approximately straight posterior carapace margin, abbreviated and undivided anterior tergites, a large sixth tergite, and fused posterior tergites. The chasmataspidid closely resembles Diploaspis casteri from the Emsian assemblage of Alken an der Mosel, but is readily discernible as a new species, D. muelleri, by a strong tuberculation of its dorsal integument. With only fragmentary opisthosomal remains available, the trigonotarbids cannot be placed in known taxa with any certainty at this time.

A NEW SYNZIPHOSURINE (CHELICERATA: XIPHOSURA) FROM THE LATE LLANDOVERY (SILURIAN) WAUKESHA LAGERSTÄTTE, WISCONSIN, USA

Abstract A new synziphosurine (Chelicerata:Xiphosura) is described from the Late Llandovery (Silurian) Konservat-Lagerstätte of Waukesha, Wisconsin, USA. Venustulus waukeshaensis n.gen. and sp. is characterized by a semicircular carapace with a slightly procurved posterior margin lacking genal spines and an opisthosoma composed of 10 freely articulating segments, divided into a preabdomen of seven segments with blunt pleurae and a postabdomen of three segments lacking pleurae. The tail spine is short and styliform. This is the earliest known unequivocal synziphosurine, extending their fossil record from the Wenlock to the Llandovery, and only the second species to be described with prosomal appendages; the presence of six pairs (a pair of chelicerae and five pairs of walking legs) contrasts with the seven in the synziphosurine Weinbergina opitzi, but is comparable to the number in modern horseshoe crabs. V. waukeshaensis n. gen. and sp. is not assigned to a family here pending a wider revision, but it bears most resemblance to the Weinberginidae.

An Upper Carboniferous eurypterid trackway from Mostyn, Wales

A trackway previously attributed to the activities of an ambulatory fish (Buckland (1843) Proceedings of the Geological Society , 4 , 204) is reinterpreted as that of a large heteropodous arthropod utilizing a hexapodous gait, the most likely candidate being a eurypterid. The trackway is assigned to Palmichnium pottsae ichnosp. nov.

Kiaeropterus (Eurypterida; Stylonurina) recognized from the Silurian of the Pentland Hills

Synopsis Eurypterus cyclophthalmus Laurie, 1892 from the Llandovery of the Pentland Hills, Scotland, is redescribed and assigned to the stylonurid eurypterid genus Kiaeropterus Waterston. 1979, previously only known from Kiaeropterus ruedemanni (Størmer, 1934) from the Wenlock of Norway. Another species previously assigned to Kiaeropterus, K. otisius Clarke 1907, is reassigned to the previously monotypic genus Clarkeipterus Kjellesvig-Waering 1966. The genus Kiaeropterus shares a previously unrecognized synapomorphy with the genus Brachyopterus Størmer 1951, namely a large bulbous ‘ocellar area’. In Kiaeropterus this area is cardioid whereas it is triangular in Brachyopterus. The two genera also share a number of less significant characters such as large anteriorly converging crescentic eyes, a lack of cuticular ornament and podomeres of the prosomal appendages with pronounced ridges, supporting a phylogenetic relationship between Kiaeropterus and Brachyopterus.

Bembicosoma re-examined: a xiphosuran from the Silurian of the North Esk Inlier, Pentland Hills, Scotland

The Silurian arthropod Bembicosoma pomphicus Laurie, 1899 is re-studied in relation to other Palaeozoic chelicerate taxa. All three known specimens of Bembicosoma originate from the Silurian (late Llandovery) Eurypterid Bed of the Gutterford Burn Flagstones, Reservoir Formation, Pentland Hills, Scotland. Bembicosoma is removed from its previous tentative assign- ment to Eurypterida and re-assigned to Xiphosura. A morphological reconstruction of this taxon is presented for the first time. This work continues a reappraisal of the systematics of a number of taxa that belong within the synziphosurines, a loose grouping of early Palaeozoic chelicerate arthropods aligned with the Xiphosura (horseshoe crabs), but which have been mistakenly identified as eurypterids in the past. Bembicosoma is significant as it is one of the earliest known synziphosurines.

On the Emsian (Early Devonian) arthropods of the Rhenish Slate Mountains: 3. The chasmataspididDiploaspis

New specimens of the chasmataspidDiploaspis casteriStørmer, 1972 (Chelicerata: Chasmataspidida) are described from the late Lower Emsian of Alken an der Mosel, Germany. Chasmataspidids represent a distinct clade within Chelicerata, sharing characters with both xiphosurans and eurypterids.Diploaspis is significant in having the most complete appendage series of any known chasmataspidid, while we question previous interpretations of the ventral preabdominal plate.Diploaspis has unmineralized cuticle and is therefore preserved with a number of different morphologies. Study of both our new fossils andStørmer’s type material suggests that the co-occurring Alken fossilHeteroaspis novojiloviStørmer, 1972 is a preservational variant, which is regarded here as a junior synonym, ofD. casteri.KurzfassungNeufunde vonDiploaspis casteriStørmer, 1972 (Chelicerata: Chasmataspidida) aus dem oberen UnterEmsium von Alken an der Mosel werden beschrieben. Die Chasmataspididen repräsentieren eine eigenständige Gruppe innerhalb der Chelicerata, welche Merkmalsübereinstimmungen sowohl mit Xiphosuren als auch mit Eurypteriden aufweist.Diploaspis kommt unter allen bekannten Chasmataspididen eine besondere Bedeutung zu, da seine Extremitäten am besten bekannt sind. Allerdings bezweifeln wir die früheren Interpretationen des ventralen praeabdominalen Schildes. Aufgrund der nicht-mineralisierten Cuticula lassen die Funde vonDiploaspis verschiedene Erhaltungszustände und damit morphologische Unterschiede erkennen. Die Untersuchung der Neufunde unter Einbeziehung vonStørmer’s Typusmaterial lässt den Schluss zu, dass der ebenfalls von Alken beschriebeneHeteroaspis novojiloviSt0ørmer, 1972 eine erhaltungsbedingte Variante und folglich ein jüngeres Synonym vonD. casteri darstellt.