O. Erik Tetlie

Giant claw reveals the largest ever arthropod

The fossil record has yielded various gigantic arthropods, in contrast to their diminutive proportions today. The recent discovery of a 46 cm long claw (chelicera) of the pterygotid eurypterid (‘sea scorpion’) Jaekelopterus rhenaniae, from the Early Devonian Willwerath Lagerstätte of Germany, reveals that this form attained a body length of approximately 2.5 m—almost half a metre longer than previous estimates of the group, and the largest arthropod ever to have evolved. Gigantism in Late Palaeozoic arthropods is generally attributed to elevated atmospheric oxygen levels, but while this may be applicable to Carboniferous terrestrial taxa, gigantism among aquatic taxa is much more widespread and may be attributed to other extrinsic factors, including environmental resources, predation and competition. A phylogenetic analysis of the pterygotid clade reveals that Jaekelopterus is sister-taxon to the genus Acutiramus, and is among the most derived members of the pterygotids, in contrast to earlier suggestions.

THE FOSSILIZATION OF EURYPTERIDS: A RESULT OF MOLECULAR TRANSFORMATION

Abstract The fossil remains of eurypterid cuticles in this study yield long-chain (<C9 to C22) aliphatic components similar to type II kerogen during pyrolysis–gas chromatography/mass spectrometry, in contrast to the chitin and protein that constitute the bulk of modern analogs. Structural analysis (thermochemolysis) of eurypterid cuticles reveals fatty acyl moieties (derived from lipids) of chain lengths C7 to C18, with C16 and C18 components being the most abundant. The residue is immune to base hydrolysis, indicating a highly recalcitrant nature and suggesting that if ester linkages are present in the macromolecule, they are sterically protected. Some samples yield phenols and polyaromatic compounds, indicating a greater degree of aromatization, which correlates with higher thermal maturity as demonstrated by Raman spectroscopy. Analysis (including thermochemolysis) of the cuticle of modern scorpions and horseshoe crabs, living relatives of the eurypterids, shows that C16 and C18 fatty acyl moieties likewise dominate. If we assume that the original composition of the eurypterid cuticle is similar to that of living chelicerates, fossilization likely involves the incorporation of such lipids into an aliphatic polymer. Such a process of in situ polymerization accounts for the fossil record of eurypterids.

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.

Phylogeny and palaeoecology of the Adelophthalmoidea (Arthropoda; Chelicerata; Eurypterida)

Synopsis A phylogenetic analysis of the monophyletic superfamily Adelophthalmoidea suggests that there is a basal, hitherto unrecognised genus, Eysyslopterus gen. nov., in the clade, on the basis of carapace shape, anterior ornament and eye position. The two comparatively poorly known genera Pittsfordipterus and Bassipterus form a relatively basal clade and are united by their shared possession of elongated eyes and a type A genital appendage consisting of two articles forming a complex distal termination. The genera Parahughmilleria and Nanahughmilleria are represented in the analysis by only one well‐known species each and the monophyly of these two genera remains untested. The geologically long‐lasting Adelophthalmus is monophyletic and supported by a number of synapomorphies. The clade probably had a marine origin. Most known representatives are brackish (estuarine‐deltaic) or freshwater (laminated lacustrine‐fluvial) inhabitants, but with a marine influence commonly encountered within the sequences. The fossil record of the clade is relatively poor with a Relative Completeness Index value of between 31 and 34%. However, the fit between phylogeny and stratigraphical occurrences of the taxa analysed is very good (Stratigraphic Consistency Index = 0.73; Gap Excess Ratio = 0.96–0.97). The sister group of Adelophthalmus, the genus Parahughmilleria, is reported for the first time from the Silurian of Lesmahagow, Scotland and these specimens are questionably referred to P. cf. hefteri, previously known only from the Siegenian and Emsian of western Germany and Luxembourg.

Geralinura Carbonaria (Arachnida; Uropygi) from Mazon Creek, Illinois, USA, and the Origin of Subchelate Pedipalps in Whip Scorpions

Abstract The whip scorpions (Arachnida: Uropygi) from the Pennsylvanian Coal Measures of Mazon Creek, Illinois, USA are restudied. Four Mazon Creek uropygid specimens have previously been described and a fifth is added here. Contrary to earlier reports, none of the specimens lack eyes and the sternum is similarly shaped in all the specimens. Consequently, the two younger names, Geralinura similis Petrunkevitch, 1913 and G. gigantea Petrunkevitch, 1913 are here treated as junior synonyms of G. carbonaria Scudder, 1884. The morphology of the pedipalps is more like those of some modern amblypygids, being spiniferous and non-chelate, suggesting the subchelate palps found in all Recent whip scorpions is an apomorphy not yet incorporated into the bodyplan of G. carbonaria. Indeed, subchelate palps also seem to be absent in other species of this age. For completeness, we summarise here the six Pennsylvanian whip scorpions currently recognised—including sketch reconstructions—with comments on further differences between the Paleozoic and living taxa. Geralinura Scudder, 1884 is reserved for G. carbonaria and the British species G. britannica Pocock, 1911. Prothelyphonus Frič, 1904 is reinstated for the Czech species P. bohemicus (Kušta, 1884). Parageralinura gen. nov. is proposed for the widely overlooked Dutch species P. neerlandica (Laurentiaux-Vieria and Laurentiaux, 1961) and the German species P. naufraga (Brauckmann and Koch, 1983). All the Coal Measures whip scorpion genera are treated here as plesion taxa, basal to the Thelyphonidae, which can be defined as whip scorpions with a fully subchelate pedipalp, the chelae formed from large and distinct patellar and tibial apophyses.

Two new Silurian species of Eurypterus (Chelicerata: Eurypterida) from Norway and Canada and the phylogeny of the genus

Synopsis A new species of Eurypterus from the Wenlock of Ringerike, Norway is described as E. hankeni sp. nov., based on fine pustular ornament on the carapace and opisthosoma, an enlarged distal podomere of the swimming leg and long angular epimera on the pretelson. Eurypterus species are reviewed: the oldest species, E. minor Laurie, 1898 from the Llandovery of the Pentland Hills in Scotland is redescribed and diagnosed as having eyes with large palpebral lobes, posterior second order opisthosomal differentiation, a coarse pustular ornament on both carapace and tergites and lacking the rows of raised scales found in other representatives of the genus. Material described previously and left in open nomenclature from the Late Ludlow of Somerset Island, Canada, is here named E. leopoldi sp. nov. It is relatively similar to E. pittsfordensis, but differs in the rhombiovate outline of the metastoma. An overview of morphological features carrying phylogenetic information in Eurypterus is provided. A phylogenetic analysis indicates that the earlier‐used gen us, Baltoeurypterus Størmer, 1973, is not monophyletic and even use of the name for its type species only (and its sister taxon) will render Eurypterus paraphyletic, unless assigning most terminals to new genera. This is not considered appropriate and the genus name Eurypterus is here proposed for use for all species, including the three previously assigned to Baltoeurypterus.

On the Emsian (Early Devonian) arthropods of the Rhenish Slate Mountains: 4. The eurypteridsAlkenopterus andVinetopterus n. gen. (Arthropoda: Chelicerata)

Recently collected material of Early Devonian eurypterids (Chelicerata: Eurypterida) from the Rhenish Slate Mountains is described and compared to the reexamined type material ofDrepanopterus struveiStørmer, 1974 andAlkenopterus brevitelsonStørmer, 1974, both from the Emsian of Alken an der Mosel.Vinetopterus martini n. gen., n. sp., from Siegenian strata of the newly detected eurypterid localities Burglahr and Hombach in the Westerwald, is described.D. struvei is transferred toVinetopterus n. gen.Vinetopterus n. gen. is diagnosed as having short prosomal appendage VI ofDrepanopterus-type A, and a first order opisthosomal differentiation. A second species from the Siegenian of Burglahr is described asAlkenopterus burglahrensis n. sp. The new family Alkenopteridae, diagnosed by possessing at least two pairs of non-spiniferous legs, V ofDrepanopterus-type B and VI ofAlkenopterus-type, is proposed to accomodateAlkenopterus. The palaeoecology of Burglahr and Hombach is briefly discussed and the habitat of these eurypterids is interpreted as representing a shallow water environment in a deltaic setting with marine or brackish influence.KurzfassungNeu aufgefundene Eurypteriden aus dem Unterdevon des Rheinischen Schiefergebirges werden beschrieben und mit dem Typusmaterial zuDrepanopterus struveiStørmer, 1974 andAlkenopterus brevitelsonStørmer, 1974 aus dem Emsium von Alken an der Mosel verglichen.Vinetopterus martini n. gen., n. sp. aus dem Siegenium von Burglahr und Hombach im Westerwald wird beschrieben.D. struvei wird zu der GattungVinetopterus n. gen. gestellt, die durch folgende Merkmale diagnostiziert wird: Eine kurze prosomale Extremität VI vomDrepanopterus-Typ A und eine opisthosomale Differenzierung ersten Grades. Eine zweite Art, ebenfalls aus dem Siegenium von Burglahr, wird alsAlkenopterus burglahrensis n. sp. beschrieben. Die hinteren prosomalen Beinpaare (V–VI) vonAlkenopterus sind unbestachelt, aber so unterschiedlich gebaut, dass sie sich zwei getrennten Typen zuordnen lassen. Die neue Familie Alkenopteridae, diagnostiziert durch den Besitz einer 5. prosomalen Extremität vomDrepanopterus-Typ B und einer 6. Extremität vomAlkenopterus-Typ, wird vorgeschlagen. Paläoökologische Aspekte hinsichtlich der beiden neu entdeckten Eurypteriden-Fundpunkte werden kurz andiskutiert und der Lebensraum dieser Eurypteriden als ein Flachwasser-Habitat innerhalb eines Delta-Komplexes, mit marinem oder brackischem Einfluss, interpretiert.

The first Silurian chasmataspid, Loganamaraspis dunlopi gen. et sp. nov. (Chelicerata: Chasmataspidida) from Lesmahagow, Scotland, and its implications for eurypterid phylogeny

A new chasmataspid (Chelicerata: Chasmataspidida) is described from the Early Silurian (Late Llandovery-Early Wenlock) of Lesmahagow, Scotland, as Loganamaraspis dunlopi gen. et sp. nov. It is distinguished from related forms by the low tapering ratio of the postabdomen, pediform sixth prosomal appendage and a heart-shaped metastoma. Additionally, a genital operculum with a genital appendage is preserved. The recognisable morphology of L. dunlopi gen. et sp. nov. bridges some of the gap between the Ordovician Chasmataspididae and the Devonian Diploaspididae. Traces of the gut are reported for the first time from a chasmataspid. Chasmataspids are regarded as sister group to the eurypterids: an anterior opercular plate anterior to the genital appendage in L. dunlopi gen. et sp. nov. is regarded as homologous to the anterior opercular plate of the three-segmented genital operculae of Dolichopterus and Stylonurina. This is considered a plesiomorphic character within Eurypterida, whilst the two-segmented genital operculum (with deltoid plates) of Eurypterina is considered apomorphic.

The systematics and phylogeny of the Stylonurina (Arthropoda: Chelicerata: Eurypterida)

The first well-resolved phylogeny of stylonurine eurypterids (30 taxa, 58 characters) is presented, prompting a taxonomic revision at the familial and superfamilial levels. The monophyletic suborder Stylonurina consists of four superfamilies: Rhenopteroidea, Stylonuroidea, Kokomopteroidea and Hibbertopteroidea. The enigmatic hibbertopterids – large sweep-feeding forms from the Carboniferous to end-Permian – are therefore demonstrated to be an in-group Stylonurina clade, within Eurypterida, in contrast to some earlier hypotheses. Furthermore, the genus Drepanopterus is shown to be polyphyletic: ‘Drepanopterus’ bembycoides is transferred to Moselopteridae fam. nov. along with Moselopterus and Vinetopterus at the base of the Eurypterina, defined by their possession of a pediform appendage VI bearing a modified podomere 7a. Evolution towards a sweep-feeding mode of life occurred independently in stylonuroids and hibbertopteroids, involving either multiple rows of fixed spines on the prosomal appendages (in stylonuroids) or paired movable flattened spines (‘blades’) on the prosomal appendages alongside a posteriorly cleft metastoma and coxal laden (in hibbertopteroids). The Stylonurina have a relatively poor fossil record (RCI 15%), when compared to more derived Eurypterina clades (e.g. Adelophthalmoidea RCI 66%; Pterygotoidea RCI 53%), but is relatively more complete than basal Eurypterina clades (RCI -21%). The fit between phylogeny and stratigraphical occurrences of stylonurid taxa is good (SCI 0.65 and GER 0.77, with only 0.3% of 1000 randomisation tests yielding greater congruence; GER* 0.995), and generic-level collector curves of the Stylonurina and Eurypterina show no major discrepancies in their sampling histories. These differences could be explained by geographic collection bias, taxa having different habitat preferences (and hence fossilisation potential), and ontogenetic factors: these results support previous suggestions that stylonurine eurypterids are oversplit.

Phylogeny of the basal swimming eurypterids (Chelicerata; Eurypterida; Eurypterina)

Synopsis The phylogeny of a broad selection of taxa at the base of the monophyletic Eurypterina (swimming eurypterids) is analysed. The results suggest that Onychopterella is the most basal of these forms, in agreement with its early stratigraphic occurrence. One step up from Onychopterella is a split between the superfamily Eurypteroidea and a clade comprising the four other clades in Eurypterina: Mixopteroidea, Waeringopteroidea, Adelophthalmoidea and Pterygotoidea. Eurypteroidea is composed of two major clades; the Eurypteridae consists of most species of Eurypterus and North American representatives of Erieopterus. The Dolichopteridae, numerically less species‐rich, but more morphologically diverse, consists of Dolichopterus, Ruedemannipterus, Buffalopterus, Strobil‐opterus, Syntomopterus and most likely ’Eurypterus’ minor. Polyphyly of Eurypterus and paraphyly of Onychopterella differ from present taxonomic assignments. Not surprisingly, the fossil record of the clade is shown to be very poor as expected for animals lacking a mineralised exoskeleton. This is reflected in a low Relative Completeness Index (RCI) value of -41%.