Addressing the Chengjiang conundrum: A palaeoecological view on the rarity of hurdiid radiodonts in this most diverse early Cambrian Lagerstätte

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

“…So far, radiodonts are restricted to the shales of the Wellsville Mountains, whereas bivalved panarthropods are also found at the High Creek and Spence Gulch localities, in shallower water carbonates (Maxey, 1958; Liddell et al, 1997; Kimmig et al, 2019b; unpublished data, Kimmig, 2021). This difference in distribution could have several explanations: (1) it might be that hurdiid radiodonts preferred deeper-water environments, an explanation indeed offered for their rarity in early Cambrian deposits (Wu et al, 2022); (2) there could be taphonomic factors that allowed radiodonts to be preserved in the Wellsville Mountains strata that were not present at other localities (Whitaker et al, 2022); or (3) this could be due to collection biases, because the Wellsville Mountains localities have been extensively excavated, whereas the other localities have not been sampled to the same extent (Whitaker and Kimmig, 2020). This difference in distribution also applies in general to the abundance of panarthropod and other species in the Spence Shale, because the Wellsville Mountain localities, especially Antimony Canyon and Miners Hollow, are the only known localities for many of the species described (Conway Morris et al, 2015; Legg and Pates, 2017; Kimmig et al, 2019b; Whitaker and Kimmig, 2020).…”

Amplectobeluid Radiodont Guanshancaris gen. nov. from the Lower Cambrian (Stage 4) Guanshan Lagerstätte of South China: Biostratigraphic and Paleobiogeographic Implications

“…The apparent decline of amplectobeluids after Cambrian Stage 4 may be related to the tectonic, climate, and geochemical changes at the Early–Middle Cambrian boundary (EMC), which is also the reason which caused the mass extinction event of archaeocyathids and redlichiid/olenellid trilobites (ROECE) [ 73 ], such as volcanically [ 74 , 75 , 76 ] or eustatically [ 76 , 77 , 78 ] associated redox, carbon negative excursions [ 73 ], and the oligotrophic environment caused by aggravated N loss, as well as enhanced P input [ 78 ]. Hurdiids thrived from the Wuliuan onwards [ 79 ], which may indicate their interspecific competitive relationship with amplectobeluids of the same ecological niche.…”

“…According to the pattern of the paleogeographic distribution of amplectobeluids, this group occurred in South China and Laurentia from Cambrian Stage 3 to Drumian, restricted to the subtropical to tropical belt ( Figure 7 ). Thus, in contrast to hurdiids [ 79 ], amplectobeluids have the preference for warm water, as seen in anomalocaridids and tamisiocaridids [ 49 , 80 ], which may be controlled by changes in sea temperatures and climate zones.…”

A large pelagic lobopodian from the Cambrian Pioche Shale of Nevada

“…A monophyletic Peytoiidae is rooted under equal weighting at two recently discovered fossils from the Chengjiang Fauna (Wu et al, 2022) attributed to Peytoiidae, but which both possess posteriorly oriented pectinate auxiliary spines, in contrast to the forward-facing or mesially oriented pectinate endites of all other peytoiids. The family name Peytoiidae is employed rather than "Hurdiidae" because, as pointed out by Greenfield (2023), the family name Hurdiidae has yet to be properly established following ICZN standards, and the name Peytoiidae (Conway Morris and Robison, 1982) is, as the oldest and only available name for the clade, the correct name to use.…”

“…These animals, known from only a small number of species, include the siberiids (three or four species), the "gilled lobopodians" (three species), and the opabiniids (three or four species). Siberiids, which essentially resemble their onychophoran-branch relatives but with more obvious adaptations for predation, may have been some of the first raptorial animals on the planet according to phylogenetic bracketing (Howard et al, 2022), while opabiniids, known only from a single species before the recent descriptions of Utaurora comosa Pates et al, 2022(Pates et al, 2022a and two specimens from the Ordovician of Wales (Pates et al, 2022b), are famously unique, even among other Cambrian taxa. The gilled lobopodians are perhaps some of the least well understood, being known only from two species from the Sirius Passet Lagerstätte of Greenland and, questionably, the recently described Utahnax vannieri Lerosey-Aubril and Ortega-Hernandez, 2022.…”