The phylogeny of fossil whip spiders

Abstract

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. 315 Ma) 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. 52 Ma) Cambay amber, and Kronocharon prendinii Engel & Grimaldi, 2014 from Cretaceous (ca. 99 Ma) Burmese amber. We recovered relationships of the form ((Graeophonus (Paracharonopsis + Paracharon)) + (Charinus (Stygophrynus (Kronocharon (Charon (Musicodamon + Paraphrynus)))))). 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 (= Paracharonopsis + Paracharon). 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.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-017-0931-1) contains supplementary material, which is available to authorized users.

Sexual dimorphism in the size and shape of the raptorial pedipalps of Giant Whip Spiders (Arachnida: Amblypygi)

“…Amblypygids are represented by c. 190 species from five families (Garwood et al, 2017) and occur on six continents. Although amblypygids are more prevalent in tropical forests, having achieved a near pantropical distribution, they have also colonized other environments such as caves, savannahs and semi-desert regions (Weygoldt, 2000).…”

“…Adults develop a number of additional smaller spines. The two distal most spines on the tibia also grow towards each other in mature individuals, creating a distal catching basket thought to be important in capture prey (Weygoldt, 2000;Garwood et al, 2017).…”

“…1). In several families, the terminal tibial spines create a 'catching basket' (Weygoldt, 1996;Prendini, Weygoldt & Wheeler, 2005;Garwood et al, 2017). Pedipalp size and shape is markedly different between species and is often taxonomically informative (Weygoldt, 1996(Weygoldt, , 2000.…”

Origin of spiders and their spinning organs illuminated by mid-Cretaceous amber fossils

“…Arthropoda; Chelicerata; Arachnida; Serikodiastida; Uraraneida (total group) Phylogenetic analyses. Following the recommendations of Prendini 17 we coded individual species instead of a terminal called "Uraraneida" that combined information from multiple species in the original data matrix of Garwood, et al 13 , which in turn evolved from prior matrices 7,11,18 (See Suppl. Information for the list of characters and codings).…”

“…A third fossil, Idmonarachne brasieri, from the Late Carboniferous of Montceau-les-Mines, France, was recently described 7 as a spider-like arachnid with spider chelicerae, a pedicel separating prosoma and opisthosoma, and a segmented opisthosoma lacking spinnerets or a flagellum. While Uraraneida was not tested for its monophyly (the two uraraneid fossils were combined into a single composite terminal), phylogenetic analyses based on an extensive morphological data matrix for living and extinct arachnids 11,12 have suggested a sister group relationship of Araneae + Idmonarachne 7,13 , with uraraneids branching earlier, giving the impression that Uraraneida and Idmonarachne are some sort of stem group Araneae that became extinct around the time that spiders started diversifying.…”