Disc-shaped fossils resembling porpitids or eldonids from the early Cambrian (Series 2: Stage 4) of western USA

Abstract

The morphology and affinities of newly discovered disc-shaped, soft-bodied fossils from the early Cambrian (Series 2: Stage 4, Dyeran) Carrara Formation are discussed. These specimens show some similarity to the Ordovician Discophyllum Hall, 1847; traditionally this taxon had been treated as a fossil porpitid. However, recently it has instead been referred to as another clade, the eldonids, which includes the enigmatic Eldonia Walcott, 1911 that was originally described from the Cambrian Burgess Shale. The status of various Proterozoic and Phanerozoic taxa previously referred to porpitids and eldonids is also briefly considered. To help ascertain that the specimens were not dubio- or pseudofossils, elemental mapping using energy dispersive X-ray spectroscopy (EDS) was conducted. This, in conjunction with the morphology of the specimens, indicated that the fossils were not hematite, iron sulfide, pyrolusite, or other abiologic mineral precipitates. Instead, their status as biologic structures and thus actual fossils is supported. Enrichment in the element carbon, and also possibly to some extent the elements magnesium and iron, seems to be playing some role in the preservation process.

New soft-bodied panarthropods from diverse Spence Shale (Cambrian; Miaolingian; Wuliuan) depositional environments

“…Remarks. — Tuzoia guntheri has been previously reported from the Cambrian (Wulian to Drumian) of the Great Basin and the Drumian Rockslide Formation of northern Canada (Robison and Richards, 1981; Liebermann, 2003; Vannier et al, 2007; Kimmig and Pratt, 2015), but this is its first record in the Spence Shale.…”

“…The Great Basin of the western United States preserves numerous Cambrian (Stage 3 to Guzhangian) Burgess Shale-type (BST) deposits (Robison et al, 2015; Foster and Gaines, 2016; Lieberman et al, 2017; Kimmig, 2021). The best known examples are the Pioche Formation of Nevada (Lieberman, 2003; Kimmig et al, 2019a), the Spence Shale Lagerstätte (Spence Shale from here on) of Utah and Idaho (Kimmig et al, 2019b; Whitaker and Kimmig, 2020), the Drum Mountains and House Range Wheeler Formation Lagerstätten (Robison et al, 2015; Lerosey-Aubril et al, 2020a), the Marjum Formation (Robison et al, 2015; Leibach et al, 2021; Pates et al, 2021a), and the Weeks Formation (Lerosey-Aubril et al, 2018).…”

Stranger than a scorpion: a reassessment of Parioscorpio venator, a problematic arthropod from the Llandoverian Waukesha Lagerstätte

“…A similar phenomenon has been seen on Ottoia fossils from Burgess‐Shale‐type deposits (Broce & Schiffbauer 2017) and in the patchy light kerogenization of visibly carbonaceous discoidal fossils from the early Cambrian Carrara Formation (Lieberman et al . 2017). Indeed, attempts to elementally map the composition of the dark film of UWGM2764 (Fig.…”

A hydrozoan from the eurypterid-dominated Silurian Bertie Group Lagerstätten of North America

“…Disc-shaped fossils are often difficult to assign to a taxonomic group (Stanley, 1986; Lieberman et al, 2017; Landing et al, 2018; MacGabhann et al, 2019) as they normally represent soft-bodied organisms that have undergone modification during decay and fossilization. Most such fossils are assigned to one of three groups: cnidarian medusae (Young and Hagadorn, 2010, 2020), eldonids (MacGabhann et al, 2019), or capitate hydrozoans (Fryer and Stanley, 2004).…”

“…They are characterized by a coiled sac at their center that is interpreted as a coelom surrounding the gut (MacGabhann et al, 2019). The disc comprises internal lobes and radial fibers that bifurcate in a regular pattern (Lieberman et al, 2017; MacGabhann et al, 2019). The nature of their preservation indicates that the disc was composed of decay-resistant carbonaceous material (MacGabhann et al, 2019).…”