The diverse radiodont fauna from the Marjum Formation of Utah, USA (Cambrian: Drumian)

Abstract

Radiodonts have long been known from Cambrian deposits preserving non-biomineralizing organisms. In Utah, the presence of these panarthropods in the Spence and Wheeler (House Range and Drum Mountains) biotas is now well-documented. Conversely, radiodont occurrences in the Marjum Formation have remained scarce. Despite the large amount of work undertaken on its diverse fauna, only one radiodont (Peytoia) has been reported from the Marjum Biota. In this contribution we quadruple the known radiodont diversity of the Marjum fauna, with the description of the youngest members of two genera, Caryosyntrips and Pahvantia, and that of a new taxon Buccaspinea cooperi gen. et sp. nov. This new taxon can be identified from its large oral cone bearing robust hooked teeth with one, two, or three cusps, and by the unique endite morphology and organisation of its frontal appendages. Appendages of at least 12 podomeres bear six recurved plate-like endites proximal to up to four spiniform distal endites. Pahvantia hastata specimens from the Marjum Formation are particularly large, but otherwise morphologically indistinguishable from the carapace elements of this species found in the Wheeler Formation. One of the two new Caryosyntrips specimens can be confidently assigned to C. camurus. The other bears the largest spines relative to appendage length recorded for this genus, and possesses endites of variable size and unequal spacing, making its taxonomic assignment uncertain. Caryosyntrips, Pahvantia, and Peytoia are all known from the underlying Wheeler Formation, whereas isolated appendages from the Spence Shale and the Wheeler Formation, previously assigned to Hurdia, are tentatively reidentified as Buccaspinea. Notably, none of these four genera occurs in the overlying Weeks Formation, providing supporting evidence of a faunal restructuring around the Drumian-Guzhangian boundary. The description of three additional nektonic taxa from the Marjum Formation further documents the higher relative proportion of free-swimming species in this biota compared to those of the Wheeler and Weeks Lagerstätten. This could be related to a moderate deepening of the basin and/or changing regional ocean circulation at this time.

Furongian (Jiangshanian) occurrences of radiodonts in Poland and South China and the fossil record of the Hurdiidae

“…The Burgess Shale biota shows the greatest generic diversity of hurdiids in the Wuliuan (four genera: Cambroraster, Hurdia, Peytoia, Stanleycaris; Daley & Budd, 2010 and references therein;Daley, Budd & Caron, 2013a;Pates, Daley & Ortega-Hernández, 2018a). Similar generic diversities, but incomparably lower abundances are observed in the Drumian Wheeler-House Range (Buccaspinea, Pahvantia, Peytoia, Stanleycaris) and Marjum (Buccaspinea, Cambroraster, Pahvantia, Peytoia) biotas of Utah (Pates, Daley & Ortega-Hernández, 2018a;Pates, Daley & Lieberman, 2018b;Lerosey-Aubril et al, 2020;Pates et al, 2021a). This greater taxonomic diversity of the group in the Miaolingian is all the more remarkable that it is almost exclusively documented by Laurentian biotas.…”

“…The insufficient preservation of the new Chinese specimen prevents a confident assignment at a lower systematic rank, but it remains easily distinguishable from most representatives of the Hurdiidae (Table 1). The family includes the genera Aegirocassis, Buccaspinea, Cambroraster, Cordaticaris, Hurdia, Pahvantia, Peytoia, Stanleycaris, Ursulinacaris, and possibly Schinderhannes and Zhenghecaris (Pates et al, 2021a). The endites of the frontal appendage from Guole are laminiform, unlike in Ursulinacaris, and narrowly-spaced, unlike in both Stanleycaris and Ursulinacaris (Pates, Daley & Ortega-Hernández, 2017;Pates, Daley & Ortega-Hernández, 2018a;Pates, Daley & Butterfield, 2019;Moysiuk & Caron, 2021).…”

“…The overwhelming majority of Cambrian Konservat-Lagerstätten, including the most studied ones (Caron & Rudkin, 2009;Zhao et al, 2011;Hu et al, 2013;Hou et al, 2017;Pates, 2018;Liu et al, 2018;Moysiuk & Caron, 2019). Radiodonts are iconic of Cambrian Epoch 2-Miaolingian Burgess Shale-type biotas, each of which typically include several species (Pates et al, 2021a). Yet, their fossil record extends to the Ordovician, possibly the Devonian (Kühl, Briggs & Rust, 2009), although only one of the four families composing the group-the Hurdiidae-is known to occur in post-Miaolingian strata.…”

“…Traditionally regarded as free-swimming apex predators ( Paterson et al, 2011 ), these organisms have proved remarkably diverse in size (millimetric to metric) and morphology, and are now reconstructed as having played various ecological roles in the early animal-dominated marine ecosystems ( Daley & Budd, 2010 ; Daley & Edgecombe, 2014 ; Vinther et al, 2014 ; Van Roy, Daley & Briggs, 2015 ; Lerosey-Aubril & Pates, 2018 ; Liu et al, 2018 ; Moysiuk & Caron, 2019 ). Radiodonts are iconic of Cambrian Epoch 2–Miaolingian Burgess Shale-type biotas, each of which typically include several species ( Pates et al, 2021a ). Yet, their fossil record extends to the Ordovician, possibly the Devonian ( Kühl, Briggs & Rust, 2009 ), although only one of the four families composing the group—the Hurdiidae—is known to occur in post-Miaolingian strata.…”

New opabiniid diversifies the weirdest wonders of the euarthropod lower stem group

“…Following a renaissance in radiodont research, it has been recognised that radiodonts display impressive variation in body size (milimetre to metre scale), body shape (rectangular to diamond shape in outline), inferred feeding ecology (raptorial predators, sediment sifters, filter feeders), and niche differentiation where species co-occur (e.g. Daley and Budd, 2010; Daley, Budd and Caron, 2013; Daley and Edgecombe, 2014; Vinther et al , 2014; Van Roy, Daley and Briggs, 2015; Lerosey-Aubril and Pates, 2018; Liu et al , 2018; Moysiuk and Caron, 2019; Lerosey-Aubril et al , 2020; Pates et al , 2021). In contrast, opabiniids show limited evidence for adaptations to different niches.…”