Redescription of the cheloniellid euarthropod Triopus draboviensis from the Upper Ordovician of Bohemia, with comments on the affinities of Parioscorpio venator
Abstract
Cheloniellida is a rare but significant clade of artiopod euarthropods, and a major component of Vicissicaudata alongside aglaspidids. The first cheloniellid to be described wasTriopus draboviensis, based on a single specimen from the Upper Ordovician Letná Formation in Bohemia. Because this specimen was believed to be missing its anterior,Triopus draboviensishas been the subject of considerable speculation regarding its affinities, with several authors combining various isolated cephalic shields with its trunk. Notwithstanding,Triopus draboviensishas eluded detailed restudy in the 150 years since its first description. Here we provide a redescription of the holotype and hitherto only known specimen ofTriopus draboviensis, and describe a recently discovered second partial specimen asTriopussp. It is shown that the holotype ofTriopus draboviensispreserves the complete cephalic shield, while the trunk reveals a likely articulating device, which may represent an apomorphy for Cheloniellida. Further information on the trunk morphology provided by the new specimen has allowed a complete reconstruction of the dorsal exoskeleton ofTriopus. An assessment is made of fossils previously suggested to represent the cephalic shield ofTriopus draboviensis; while it is shown that none of those fossils can be attributed toTriopus, it is reaffirmed thatDrabovaspis complexalikely does belong to Cheloniellida, makingDrabovaspisthe third cheloniellid genus known from the Letná Formation, afterTriopusandDuslia. A revised diagnosis for Cheloniellida is provided, and the recently described problematic euarthropodParioscorpio venatorfrom the Silurian of Wisconsin is firmly rejected from this clade.
- Publication:
-
Geological Magazine
- Pub Date:
- September 2022
- DOI:
- 10.1017/S0016756822000292
- Bibcode:
- 2022GeoM..159.1471V