Jason A. Dunlop

A minute fossil phoretic mite recovered by phase-contrast X-ray computed tomography

High-resolution phase-contrast X-ray computed tomography (CT) reveals the phoretic deutonymph of a fossil astigmatid mite (Acariformes: Astigmata) attached to a spiders carapace (Araneae: Dysderidae) in Eocene (44–49 Myr ago) Baltic amber. Details of appendages and a sucker plate were resolved, and the resulting three-dimensional model demonstrates the potential of tomography to recover morphological characters of systematic significance from even the tiniest amber inclusions without the need for a synchrotron. Astigmatids have an extremely sparse palaeontological record. We confirm one of the few convincing fossils, potentially the oldest record of Histiostomatidae. At 176 µm long, we believe this to be the smallest arthropod in amber to be CT-scanned as a complete body fossil, extending the boundaries for what can be recovered using this technique. We also demonstrate a minimum age for the evolution of phoretic behaviour among their deutonymphs, an ecological trait used by extant species to disperse into favourable environments. The occurrence of the fossil on a spider is noteworthy, as modern histiostomatids tend to favour other arthropods as carriers.

A redescription of some poorly known Rotliegend arachnids from the Lower Permian (Asselian) of the Ilfeld and Thuringian Forest Basins, Germany

Two poorly known trigonotarbids (Arachnida: Trigonotarbida),Eophrynus schärftScharf, 1924 andEophrynus ilfeldicusScharf, 1924 from the Lower Permian (Asselian) Ilfeld Basin in the Harz Region of Germany are redescribed. The latter is transferred to the genusAphantomartusPocock, 1911. The former resembles members of Lissomartidae, but given its incompleteness it is assigned here to Trigonotarbida incertae sedis. A phalangiotarbid (Arachnida: Phalangiotarbida) from Ilfeld described asOpiliotarbus elongatus (Scudder, 1890) represents the youngest record of this group. With respect to the genusOpiliotarbusPocock, 1910,Architarbus hoffmanniGuthörl, 1934 — one of three names erected for a lost specimen from the Upper Carboniferous of the Saar region of Germany — represents the senior synonym ofOpiliotarbus kliveriWaterlot, 1934 andGoniotarbus sararmGuthörl, 1965. The Lower Permian fossilRhabdotarachnoides simoni Haupt, 1957 from the Rotliegend of the Thuringian Forest Basin, Germany was described as an arachnid and tentatively referred to Opiliones. Since it is identified here as a coalified plant remain, this species is regarded as nomen dubium.KurzfassungZwei wenig bekannte Trigonotarbiden (Arachnida: Trigonotarbida),Eophrynus scharfiScharf, 1924 undEophrynus ilfeldicusScharf, 1924 aus dem unteren Perm (Asselian) des Ilfelder Beckens (Harz, Deutschland) werden neu bearbeitet. Die letztgenannte Art wird zur GattungAphantomartusPocock, 1911 gestellt, erstere ähnelt Vertretern der Lissomartidae, wobei die Unvollständigkeit und ungünstige Einbettungsiage des Fossilrestes eine Zuordnung zu den Trigonotarbida incertae sedis erfordern. Eine Phalangiotarbide (Arachnida: Phalangiotarbida) von Ilfeld, die gleichzeitig den jüngsten Vertreter dieser Gruppe darstellt, wird alsOpiliotarbus elongatus (Scudder, 1890) beschrieben. Innerhalb der GattungOpiliotarbusPocock, 1910, wirdArchitarbus hoffmanniGuthörl, 1934 — einer von drei Bezeichnungen, die für ein verloren gegangenes Stück aus dem Oberkarbon der Saar-Senke, Deutschland, errichtet wurden, hier Priorität geschenkt gegenüber den SynonymenOpiliotarbus kliveriWaterlot, 1934 undGoniotarbus saranaGuthörl, 1965. Das unterpermische FossilRhabdotarachnoides simoni Haupt, 1957 aus dem Rotliegend von Thüringen (Thüringer Wald-Senke, Deutschland), ehemals als Arachnidenrest beschrieben und zu den Opiliones gestellt, ist unzweifelhaft als inkohlter Pflanzenrest erkennbar und somit als nomen dubium einzustufen.

Segmentation and tagmosis in Chelicerata.

Patterns of segmentation and tagmosis are reviewed for Chelicerata. Depending on the outgroup, chelicerate origins are either among taxa with an anterior tagma of six somites, or taxa in which the appendages of somite I became increasingly raptorial. All Chelicerata have appendage I as a chelate or clasp-knife chelicera. The basic trend has obviously been to consolidate food-gathering and walking limbs as a prosoma and respiratory appendages on the opisthosoma. However, the boundary of the prosoma is debatable in that some taxa have functionally incorporated somite VII and/or its appendages into the prosoma. Euchelicerata can be defined on having plate-like opisthosomal appendages, further modified within Arachnida. Total somite counts for Chelicerata range from a maximum of nineteen in groups like Scorpiones and the extinct Eurypterida down to seven in modern Pycnogonida. Mites may also show reduced somite counts, but reconstructing segmentation in these animals remains challenging. Several innovations relating to tagmosis or the appendages borne on particular somites are summarised here as putative apomorphies of individual higher taxa. We also present our observations within the concept of pseudotagma, whereby the true tagmata - the prosoma and opisthosoma - can be defined on a fundamental change in the limb series while pseudotagmata, such as the cephalosoma/proterosoma, are expressed as divisions in sclerites covering the body without an accompanying change in the appendages.

Amblyomma birmitum a new species of hard tick in Burmese amber

Amblyomma birmitum sp. nov. is formally described as a new record from 99 Ma old Burmese amber from Myanmar. This confirms the presence of the extant hard tick genus Amblyomma C.L. Koch, 1844 (Ixodida: Ixodidae) in the Late Cretaceous. This discovery is placed in its wider context and some reports of fossil hard ticks, such as a Hyalomma C.L. Koch, 1844 in Eocene Baltic amber, are misidentifications. The genus Amblyomma belongs to the clade Metastriata, a group which probably also accommodates two extinct genera, Cornupalpatum Poinar and Brown, 2003 and Compluriscutata Poinar and Buckley, 2008, also found in Burmese amber. All three fossils are thus only a little younger than published molecular divergence time estimates (ca. 124 ± 17 Ma) for the Metastriata lineage. Amblyomma has a largely Gondwanan distribution today. However, in some biogeographical scenarios, e.g. the Samafrica model, its predicted radiation time postdates the dissolution of the original Gondwana supercontinent raising questions about how its current distribution pattern was achieved.

Smaridid Mites in Baltic and Bitterfeld Amber, with Notes on the Fossil Record of Terrestrial Parasitengona (Trombidiformes: Prostigmata)

Abstract. Three species of fossil smaridid mites (Parasitengona, Smarididae) are described based on postlarval forms. Fessonia wunderlichi sp. nov., Fessonia grabenhorsti sp. nov. and Fessonia groehni sp. nov. were discovered in Eocene (ca. 44–50 Ma) Baltic amber and the former two also in the probably younger Oligocene (ca. 23–25 Ma) Bitterfeld amber. Although Smarididae has been reported from Baltic (and other) Cenozoic amber localities, these are the first species from this group to be formally described. Fessonia wunderlichi sp. nov. and Fessonia grabenhorsti sp. nov. are also the first named mites from Bitterfeld amber, and at the same time the first examples of mite species common to both the Baltic and Bitterfeld deposits. Fessonia groehni sp. nov. is known from a single specimen originating from the Baltic deposit. Although the thickened hindlimbs seen in Fessonia wunderlichi sp. nov. resemble the modern smaridid genus Kraussiana Southcott, 1961, the structure of the crista metopica implies another extant genus — Fessonia von Heyden, 1826 — which we redefine here to accommodate the morphology of the amber species. An outline of previous findings of terrestrial Parasitengona in amber is also provided.

A Middle Devonian chasmataspid arthropod from Achanarras Quarry, Caithness, Scotland

Synopsis A new fossil of the rare and little known arthropod group Chasmataspida (Chelicerata), is described as Achanarraspis reedi gen. et sp. nov. from the Middle Devonian (late Eifelian) of Achanarras Quarry, Caithness, Scotland. This is the first known occurrence of arthropod remains from this locality. Chasmataspids appear to be closely related to eurypterids and fossils of these groups have been confused with each other in the past. Achanarraspis resembles Lower Devonian chasmataspids from Germany, the Midland Valley of Scotland and the Severnya Zemlya Archipeligo, Siberia, but is distinguished from these taxa in possessing a carapace which is distinctly longer than the preabdomen, sharp lateral epimera on all postabdominal tergites, and a distinctive telson morphology. The Middle Devonian age makes Achanarraspis the youngest chasmataspid yet known and significantly extends the known stratigraphical range of the group. Other occurrences of arthropods from the Caithness Flags are reviewed and include conchostracan crustaceans, incomplete eurypterids and a now lost xiphosuran specimen collected in the late 1800s.

A redescription of the Carboniferous arachnid Plesiosiro madeleyi Pocock, 1911 (Arachnida: Haptopoda)

Plesiosiro madeleyi Pocock, 1911, the monotypic representative of the fossil order Haptopoda Pocock, 1911 from the British Middle Coal Measures (Upper Carboniferous, Westphalian B) of Coseley, Staffordshire, is redescribed. A specimen from Sparth Bottoms, Lancashire is not a Plesiosiro and is referred to Arthropoda incertae sedis. Plesiosiro was probably a predator, having tooth-like projections on the femora for prey capture, and shows adaptations of the limbs for crawling in narrow spaces. The uncertain nature of the chelicerae, eyes and respiratory organs makes resolving the phylogenetic position of Plesiosiro difficult, though Haptopoda deserves its status as a separate order. Plesiosiro resembles both cythophthalmid and trogulid opilionids. Its broad prosoma–opisthosoma junction could be interpreted as a synapomorphy for Plesiosiro + Opiliones, but this character is not unique to these orders. Alternatively, Plesiosiro has a large, ventral opisthosomal sclerite. This is interpreted here as a genital operculum, a synapomorphy for Tetrapulmonata, and Plesiosiro is tentatively referred to this clade. Based on the synapomorphies of a divided sternum and subdivided telotarsi a relationship of the form: (Plesiosiro (Amblypygi (Thelyphonida + Schizomida))) is proposed.

The phylogeny of fossil whip spiders

BackgroundArachnids are a highly successful group of land-dwelling arthropods. They are major contributors to modern terrestrial ecosystems, and have a deep evolutionary history. Whip spiders (Arachnida, Amblypygi), are one of the smaller arachnid orders with ca. 190 living species. Here we restudy one of the oldest fossil representatives of the group, Graeophonus anglicus Pocock, 1911 from the Late Carboniferous (Duckmantian, ca. 315xa0Ma) British Middle Coal Measures of the West Midlands, UK. Using X-ray microtomography, our principal aim was to resolve details of the limbs and mouthparts which would allow us to test whether this fossil belongs in the extant, relict family Paracharontidae; represented today by a single, blind species Paracharon caecus Hansen, 1921.ResultsTomography reveals several novel and significant character states for G. anglicus; most notably in the chelicerae, pedipalps and walking legs. These allowed it to be scored into a phylogenetic analysis together with the recently described Paracharonopsis cambayensis Engel & Grimaldi, 2014 from the Eocene (ca. 52xa0Ma) Cambay amber, and Kronocharon prendinii Engel & Grimaldi, 2014 from Cretaceous (ca. 99xa0Ma) Burmese amber. We recovered relationships of the form ((Graeophonus (Paracharonopsisu2009+u2009Paracharon))u2009+u2009(Charinus (Stygophrynus (Kronocharon (Charon (Musicodamonu2009+u2009Paraphrynus)))))). This tree largely reflects Peter Weygoldt’s 1996 classification with its basic split into Paleoamblypygi and Euamblypygi lineages; we were able to score several of his characters for the first time in fossils. Our analysis draws into question the monophyly of the family Charontidae.ConclusionsOur data suggest that Graeophonus is a crown group amblypygid, and falls within a monophyletic Paleoamblypgi clade, but outside the family Paracharontidae (= Paracharonopsisu2009+u2009Paracharon). Our results also suggest a new placement for the Burmese amber genus Kronocharon, a node further down from its original position. Overall, we offer a broad phylogenetic framework for both the fossil and Recent whip spiders against which future discoveries can be tested.

Penis morphology in a Burmese amber harvestman

A unique specimen of the fossil harvestman Halitherses grimaldii Giribet and Dunlop, 2005 (Arachnida: Opiliones) from the Cretaceous (ca. 99xa0Ma) Burmese amber of Myanmar reveals a fully extended penis. This is the first record of a male copulatory organ of this nature preserved in amber and is of special importance due to the age of the deposit. The penis has a slender, distally flattened truncus, a spatulate heart-shaped glans and a short distal stylus, twisted at the tip. In living harvestmen, the penis yields crucial characters for their systematics. Male genital morphology in H. grimaldii appears to be unique among the wider Dyspnoi clade to which this fossil belongs. The large eyes in the fossil differ markedly from other members of the subfamily Ortholasmatinae to which H. grimaldii was originally referred. Based on recent data, it has been argued that large eyes may be plesiomorphic for Palpatores (i.e. the suborders Eupnoi and Dyspnoi), potentially rendering this character plesiomorphic for the fossil too. Thus, the unique structure of the penis seen here, and the probable lack of diaphanous teeth, present in all other extant non-acropsopilionid Dyspnoi, suggest that H. grimaldii represents a new, extinct family of large-eyed dyspnoid harvestmen, Halithersidae fam. nov.; a higher taxon in amber diagnosed here on both somatic and genital characters.

Scorpion Fragments from the Silurian of Powys, Wales

Summary Fragments of a fossil scorpion collected from Silurian (Ludfordian, c. 420 Ma) strata near Trecastle in Powys, Wales, are described. They represent one of the oldest records of Scorpiones, of which only five other species are known from the Silurian. Given the incomplete nature of the new material, which includes a largely complete carapace with anteriorly positioned median eyes, we cannot assign it to any particular family or genus. However, the pustulate carapace ornament and preserved pattern of sulci are reminiscent of certain, much larger, fossil scorpions such as the Devonian Praearcturus gigas Woodward, 1871 and the Carboniferous Gigantoscorpio willsi Størmer, 1963.