Trigonotarbid arachnids from the Lower Devonian (Lower Emsian) of Alken an der Mosel (Rhineland-Palatinate, SW Germany)

Abstract

New material of the trigonotarbids Alkenia and Archaeomartus from the Lower Devonian type locality Alken an der Mosel/Germany is described. Størmer's original description of Alkenia is essentially confirmed and supplemented. The genus is placed in Aphantomartidae. In contrast to earlier accounts, we show that Archaeomartus has an anterior diplotergite and a longitudinally threedivided posteriormost (ninth) tergite. The new family Archaeomartidae is proposed. Whether a marginal row of larger tubercles on the opisthosoma can be recognized is strongly influenced by the taphonomic history of the fossil, and sexual dimorphism may also be involved. Thus, we propose that Archaeomartus levis and A. tuberculatus, which can be discriminated solely by the presence or absence of this feature, are synonyms. Furthermore, morphological similarity suggests the possibility that archaeomartids, with their opisthosomal tergites divided into three plates, gave rise to the later (Carboniferous) anthracomartids, specifically through the division of the lateral plates and the ninth tergite. Finally, our reassessment of Archaeomartus shows that 'A.' roessleri Dunlop and Brauckmann, 2006 can no longer be adequately maintained in this genus. This younger species from the early Upper Carboniferous of Hagen-Vorhalle, Germany, is reassigned to Namurotarbus n. gen. as Namurotarbus roessleri n. comb. Kurzfassung Neue Funde der Trigonotarbiden Alkenia und Archaeomartus aus dem Unterdevon der Typuslokalität Alken an der Mosel werden bearbeitet. Størmers ursprüngliche Beschreibung von Alkenia wird im Wesentlichen bestätigt und ergänzt. Die Gattung wird in die Familie Aphantomartidae gestellt. Im Gegensatz zu früher geäußerten Ansichten können wir zeigen, dass Archaeomartus einen vorderen Diplotergit und einen dreigeteilten letzten (neunten) Tergit besitzt. Die neue Familie Archaeomartidae wird vorgeschlagen. Die Erkennbarkeit einer Reihe von größeren Tuberkeln entlang des OpisthosomaRandes variiert stark in Abhängigkeit von taphonomischen Faktoren. Zudem könnte sich in der Ausprägung dieses Merkmals ein möglicher Sexualdimorphismus abzeichnen. Archaeomartus levis und A. tuberculatus, die sich nur anhand dieses einen Merkmals unterscheiden lassen, werden folglich als synonym angesehen. Darüber hinaus legt die große morphologische Ü bereinstimmung die Möglichkeit nahe, dass sich ausgehend von den Archaeomartiden mit dreigeteilten, opisthosomalen Tergiten die jüngeren (karbonischen) Anthracomartiden entwickelt haben, was insbesondere mit einer weiteren Teilung der Lateralplatten und des neunten Tergiten einherging. Schließlich zeigt unsere Neuuntersuchung von Archaeomartus, dass ,,A.'' roessleri Dunlop and Brauckmann, 2006 nicht länger der Gattung zugeordnet werden kann. Diese Art aus dem frühen Oberkarbon von Hagen-Vorhalle, Deutschland wird in die M. Poschmann (&) Generaldirektion Kulturelles Erbe RLP, Direktion Landesarchäologie, Referat Erdgeschichte,

A timeline for terrestrialization: consequences for the carbon cycle in the Palaeozoic

“…Trigonotarbids belong to the stemgroup of Tetrapulmonata [69], the clade that includes Araneae (spiders), Amblypygi (whip spiders) and Uropygi (whip scorpions). Trigonotarbids are first known from the Přidolí, and have several Devonian members (see recent review in Poschmann & Dunlop [70]), some of which exhibit the characteristic two pairs of book lungs of Tetrapulmonata [71].…”

The youngest trigonotarbidPermotarbus schubertin. gen., n. sp. from the Permian Petrified Forest of Chemnitz in Germany

“…A comprehensive cladistic study of relationships among trigonotarbids is lacking, but the sequence of genera presented in this figure reflects recently published ideas on their phylogeny. These include a Palaeocharinidae-Archaeomartidae-Anthracomartidae group elucidated by Poschmann & Dunlop (2010, fig. 9), which retain well-developed lateral eye tubercles on a subquadrate, box-like carapace.…”

“…Near contemporary, but perhaps a little younger at Lower Emsian (ca. 405 Ma) are a series of further Rhineland genera, namely Alkenia Størmer, 1970 andArchaeomartus Størmer, 1970 from Alken an der Mosel (Størmer 1970;Poschmann & Dunlop 2010). Of these, Alkenia was recently reassigned to Aphantomartidae and Archaeomartus to a new family Archaeomartidae; the latter with characters intermediate between palaeocharinids and anthracomartids (Poschmann & Dunlop 2010).…”

Trigonotarbid arachnids from the Lower Devonian (Siegenian) of Bürdenbach (Lahrbach Valley, Westerwald area, Rhenish Slate Mountains, Germany)

“…The Rhenish Slate Mountains are certainly among the most important geographical areas yielding Lower Devonian terrestrial arthropods, including an array of trigonotarbid arachnids (Størmer 1970;Brauckmann 1987Brauckmann , 1994Schultka 1991;Poschmann et al 2005;Poschmann and Dunlop 2010). Although as yet confined to compressions, these fossils significantly contribute to our understanding of early trigonotarbid diversity and have the potential to reveal phylogenetic traits within the clade (cf.…”

“…Although as yet confined to compressions, these fossils significantly contribute to our understanding of early trigonotarbid diversity and have the potential to reveal phylogenetic traits within the clade (cf. Poschmann and Dunlop 2010). The present contribution aims at the systematic description of trigonotarbids from a newly detected locality of Siegenian age including an archaeomartid and the first palaeocharinid trigonotarbids from the Rhenish Devonian.…”