150-million-year-old sea spiders (Pycnogonida: Pantopoda) of Solnhofen

Abstract

Sea spiders (Pycnogonida) are strange arthropods characterized by a unique morphology, including reduced body, egg-carrying appendages, and a proboscis. This peculiar body plan dates at least as early as the first undoubted occurrence of the group, 425 million years ago in the Silurian. All extant species belong to the order Pantopoda, characterized by cylindrical legs and an unsegmented abdomen. Paleozoic fossils are much more diversified, and exhibit features very different from pantopod morphology such as a segmented abdomen, limbs specialized to swim, or even a flagellum. The few Mesozoic fossils from the single Jurassic palaeoenvironment of La Voulte-sur-Rhône (south-eastern France) instead have strong affinities to Pantopoda. Here, we investigate the morphology of nine sea spider fossils using a new photographic protocol to document morphology, combining focus stacking and differential colorization. We also describe two new species of fossil pycnogonids from the Late Jurassic of Solnhofen (southern Germany): Colossopantopodus nanus n. sp. is closely allied to a large species from La Voulte-sur-Rhône, but distinct in its smaller size; the other, ?Eurycyde golem n. sp., is the first known fossil representative of the extant family Ascorhynchidae. Seven additional specimens, too poorly preserved for taxonomic description, are illustrated. The comparisons reveal that the shallow lagoons of Solnhofen contained a diverse assemblage of pantopods. Altogether with the fauna of La Voulte-sur-Rhône, the results suggest that Pantopoda became the dominant pycnogonid taxon of both deep and shallow marine waters after the Jurassic.

Phylogenomic resolution of sea spider diversification through integration of multiple data classes

“…Our divergence time estimation unambiguously recovered an Ordovician age of sea spider diversification, a result that is independent of both the deployment of Haliestes dasos as a calibration prior, and the choice of clock model. Ancient diversification of Pycnogonida during the Ordovician is consistent with their fossil record (e.g., Jurassic sea spiders that are assignable to families) [30,31], and further suggests that Devonian sea spiders with opisthosomal segments (e.g., Flagellopantopus, Palaeoisopus) constitute stem lineages that diverged from extant Pycnogonida before the Ordovician and thereafter went extinct. A parallel evolutionary history has been reconstructed for spiders and their extinct sister group Uraraneida, which was recently shown to have survived at least until the Cretaceous [53].…”

Phylogenomic Resolution of Sea Spider Diversification through Integration of Multiple Data Classes

“…Sea spider crown group fossils from the Late Jurassic and La-Voulte-sur-Rhône were used to calibrate ingroup nodes: Palaeopycnogonides gracilis (Ammotheidae), Colossopantopodus boissinensis and Colossopantopodus nanus (Colossendeidae), and Palaeoendeis elmii (Endeidae) ( Charbonnier et al. 2007 ; Sabroux et al. 2019 ).…”

New insights into the sea spider fauna (Arthropoda, Pycnogonida) of La Voulte‐sur‐Rhône, France (Jurassic, Callovian)

“…Charbonnier et al . 2007a], 307, 310, 316 [phylogeny], 319 [reconstruction]. 2014 Colossopantopodus boissinensis ; Charbonnier et al ., p. 375, table 1.v2019 Colossopantopodus boissinensis ; Sabroux et al ., pp. 1933–1935 [text], figs 1 [diagram], 3D.…”

“…[non fig. 309 = MNHN.F.A52386]. 2014 Palaeoendeis elmii ; Charbonnier et al ., p. 375 [text], table 1. 2019 Palaeoendeis elmii ; Sabroux et al ., p. 1935 [text], fig. 1 [diagram].…”