Brittle stars from the British Oxford Clay: unexpected ophiuroid diversity on Jurassic sublittoral mud bottoms

Abstract

Abstract.-Three new ophiuran species, Enakomusium whymanae n. sp., Aspidophiura? seren n. sp., and Ophiotitanos smithi n. sp., and an unnamed specimen assignable to the genus Dermocoma are described from the Callovian to Oxfordian Oxford Clay Formation of Great Britain. These determinations are based on new finds and a critical reassessment of historic specimens. The Oxford Clay ophiuroids represent two loose assemblages, one from the middle Callovian Peterborough Member and the other from the lower Oxfordian Weymouth Member. Both assemblages accord well with coeval midshelf mud bottom ophiuroid communities in terms of taxonomic composition and relative abundance of taxa. The British Oxford Clay ophiuroids are particularly significant as they are one of the rare instances where multiple species are represented, almost exclusively, by exceptionally preserved articulated skeletons. This provides an important window into the understanding of mid-Upper Jurassic ophiuroid paleobiology.

New fossils of Jurassic ophiurid brittle stars (Ophiuroidea; Ophiurida) provide evidence for early clade evolution in the deep sea

“…nov., in contrast, has a more crownward position within the family Ophiuridae. Our analyses also included previously known fossil ophiuroids with assumed ophiurid affinities: Palaeocoma milleri and Aspidophiura seren both fall within the Ophiopyrgidae, and are in line with previous studies [6,32], whereas Ophioculina hoybergia belongs to the Ophiuridae, rather than the Ophiopyrgidae as suggested in the original description of the taxon [26]. The two species of Enakomusium are phylogenetically close to the Ophiosphalmidae and Ophiomusaidae, thus corroborating their inclusion in the suborder Ophiomusina, but our results are uncertain with respect to the relationships on family level.…”

New fossils of Jurassic ophiurid brittle stars (Ophiuroidea; Ophiurida) provide evidence for early clade evolution in the deep sea

“…nov., in contrast, has a more crownward position within the family Ophiuridae. Our analyses also included previously known fossil ophiuroids with assumed ophiurid affinities: Palaeocoma milleri and Aspidophiura seren both fall within the Ophiopyrgidae, and are in line with previous studies (6, 25), whereas Ophioculina hoybergia belong to the Ophiuridae, rather than the Ophiopyrgidae as suggested in the original description of the taxon (26). The two species of Enakomusium are phylogenetically close to the Ophiosphalmidae and Ophiomusaidae, thus corroborating their inclusion in the suborder Ophiomusina, but our results are uncertain with respect to the relationships on family level.…”

“…Aspidophiura? seren Ewin & Thuy, 2017 from the Callovian of Great Britain has much larger spine articulations placed directly at the outer distal edge, and lacks spurs along the outer proximal edge. Ophioculina hoybergia Rousseau & Thuy, 2018 from the Tithonian of Spitsbergen has a fully developed arm comb, i.e.…”

Brittle stars from the Lower Cretaceous of Patagonia: first ophiuroid articulated remains for the Mesozoic of South America

“…Specimens with articulated and largely complete skeleton are extremely rare (Spencer and Wright, 1966;Aronson, 1989;Kerr and Twitchett, 2004;Martínez et al, 2010). Systematic assessment of fossil ophiuroids has recently received increasing attention (Ewin and Thuy, 2017). Yet, knowledge of the fossil record of ophiuroids, particularly in the Lower Cretaceous, is still limited (Thuy et al, 2014).…”