Occurrence of the Ordovician-type aglaspididTremaglaspisin the Cambrian Weeks Formation (Utah, USA)

Abstract

The Guzhangian Weeks Formation preserves a diverse, yet virtually unstudied, non-trilobite arthropod fauna. Here we describe Tremaglaspis vanroyi sp. nov., the oldest representative of an enigmatic group of extinct arthropods, the Aglaspidida. Tremaglaspis was previously known from the Lower Ordovician and its morphology was regarded as particularly derived within the clade. Its occurrence in the Cambrian of Utah suggests that much of the early evolutionary history of the Aglaspidida remains unknown. A review of the environmental settings of previous aglaspidid findings suggests that these arthropods preferentially inhabited shallow-water environments, which may partially explain their limited fossil record.

Arthropod appendages from the Weeks Formation Konservat-Lagerstätte: new occurrences of anomalocaridids in the Cambrian of Utah, USA

“…Relatively little is known about the non-trilobite arthropod fauna from the Weeks Formation, but taxa such as Beckwithia typa Resser, 1931(Raasch 1939, Hesselbo 1989 and Tremaglaspis vanroyi Lerosey-Aubril et al, 2013 suggest that its composition may notably differ from those of better-known Cambrian arthropod assemblages. This is further illustrated by the description of specimen BPM 1025, which exhibits an intriguing combination of characters that do not fit with the current definitions of any fossil or modern arthropod taxa.…”

“…This is supported by the fact that the non-trilobite arthropod fauna is dominated by aglaspidids or aglaspidid-like arthropods. These organisms mostly occur in proximal, relatively shallow-water deposits (Lerosey-Aubril et al 2013), such as those of the IDB lithofacies of the St. Lawrence Formation (Furongian) in the Upper Mississippi Valley. However, the trilobite fauna suggests that there was open-marine access during the time of deposition of the Weeks Formation .…”

“…However, the exoskeletons of trilobites and aglaspidids frequently show evidence of a partial silicification (Beebe 1990, Adrain et al 2009, Lerosey-Aubril et al 2013. Internal organs (e.g.…”

A rare non‐trilobite artiopodan from the Guzhangian (Cambrian Series 3) Weeks Formation Konservat‐Lagerstätte in Utah, USA

“…The only known exception to date is the phosphatic cuticle of the aglaspidid‐like arthropod Beckwithia typa Resser, , and the aglaspidid Tremaglaspis vanroyi Lerosey‐Aubril, Ortega‐Hernández et al ., ; however, it is likely that this biomineralization represents a particularity of Aglaspidida sensu lato (Lerosey‐Aubril et al . , b ). Furthermore, the trilobites from the Weeks Formation mostly retain their original calcitic composition, although many specimens show traces of diagenetic silicification (Adrain et al .…”

“…These ‘soft‐bodied’ or weakly biomineralized organisms are predominantly represented by arthropods (Lerosey‐Aubril et al . , ; Lerosey‐Aubril ) and worms (e.g. palaeoscolecids), although sponges and a possible ctenophore (i.e.…”