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

Abstract

Radiodonta, an extinct stem-euarthropod group, has been considered as the largest predator of Cambrian marine ecosystems. As one of the radiodont-bearing Konservat-Lagerstätten, the Guanshan biota (South China, Cambrian Stage 4) has yielded a diverse assemblage of soft-bodied and biomineralized taxa that are exclusive to this exceptional deposit. “Anomalocaris” kunmingensis, the most abundant radiodont in the Guanshan biota, was originally assigned to Anomalocaris within the Anomalocarididae. Despite this taxon being formally assigned to the family Amplectobeluidae more recently, its generic assignment remains uncertain. Here, we present new materials of “Anomalocaris” kunmingensis from the Guanshan biota, and reveal that the frontal appendages possess two enlarged endites; all endites bear one posterior auxiliary spine and up to four anterior auxiliary spines; three robust dorsal spines and one terminal spine protrude from the distal part. These new observations, allied with anatomical features illustrated by previous studies, allow us to assign this taxon to a new genus, Guanshancaris gen. nov. Brachiopod shell bearing embayed injury and incomplete trilobites, associated with frontal appendages in our specimens, to some extent confirm Guanshancaris as a possible durophagous predator. The distribution of amplectobeluids demonstrates that this group is restricted to Cambrian Stage 3 to Drumian, and occurs across South China and Laurentia within the tropics/subtropics belt. Moreover, the amount and abundance of amplectobeluids evidently decreases after the Early–Middle Cambrian boundary, which indicates its possible preference for shallow water, referring to its paleoenvironmental distribution and may be influenced by geochemical, tectonic, and climatic variation.

The significance of Anomalocaris and other Radiodonta for understanding paleoecology and evolution during the Cambrian explosion

“…Amplectobelua symbrachiata has been described from the Niutitang Formation (Cambrian Stage 3-South China) (Steiner et al, 2005). The Guanshan Biota (Cambrian Stage 4-South China) is the only locality in which we find Guanshancaris kunmingensis (previously called "Anomalocaris" kunmingensis) (Wang et al, 2013;Zeng et al, 2018;Jiao et al, 2021;Zhang et al, 2023). The Latham Shale, also Stage 4 (Laurentia), has yielded Ramskoeldia cf.…”

“…Computational modelling has shown that such motions are not possible with Anomalocaris appendages (De Vivo et al, 2021), nor was their sclerotised cuticle capable of tearing a mineralised exoskeleton (Bicknell et al, 2023). Damages preserved in trilobite and nektaspid exoskeletons (Conway Morris, 1985;Nedin, 1999) and large coprolites found in Cambrian lagerstätten that contain fragments of trilobites (Nedin, 1999;Vannier and Chen, 2005) had previously been attributed to durophagous predation by radiodonts (Nedin, 1999;Klug et al, 2017;Vinn, 2018;Zong, 2021;Zhang et al, 2023). Based on the unsuitability of the frontal appendage (De Vivo et al, 2021;Bicknell et al, 2023) and oral cone (Daley and Bergström, 2012) for durophagy, Anomalocarididae are no longer considered to have been predators of mineralized shelly taxa, and instead these coprolites and damages are attributed to Redlichia and other Cambrian trilobites (Daley et al, 2013b) or gnathobase-bearing artiopodan euarthropods (Bicknell et al, 2018;2022).…”

“…Based on the unsuitability of the frontal appendage (De Vivo et al, 2021;Bicknell et al, 2023) and oral cone (Daley and Bergström, 2012) for durophagy, Anomalocarididae are no longer considered to have been predators of mineralized shelly taxa, and instead these coprolites and damages are attributed to Redlichia and other Cambrian trilobites (Daley et al, 2013b) or gnathobase-bearing artiopodan euarthropods (Bicknell et al, 2018;2022). The Amplectobeluidae taxon Guanshancaris has been suggested to have been capable of durophagy, based on its flexible proximal endites and the stout nature of the endites on intermediate podomeres, with suggested prey being trilobites and brachiopods, which show damage to their exoskeleton in specimens found closely associated with Guanshancaris (Zhang et al, 2023). Anomalocarididae and most Amplectobeluidae taxa likely consumed soft-bodied and lightly sclerotized prey items (Daley and Bergström, 2012;De Vivo et al, 2021;Bicknell et al, 2023), with Guanshancaris potentially being capable of durophagy (Zhang et al, 2023).…”

“…The Amplectobeluidae taxon Guanshancaris has been suggested to have been capable of durophagy, based on its flexible proximal endites and the stout nature of the endites on intermediate podomeres, with suggested prey being trilobites and brachiopods, which show damage to their exoskeleton in specimens found closely associated with Guanshancaris (Zhang et al, 2023). Anomalocarididae and most Amplectobeluidae taxa likely consumed soft-bodied and lightly sclerotized prey items (Daley and Bergström, 2012;De Vivo et al, 2021;Bicknell et al, 2023), with Guanshancaris potentially being capable of durophagy (Zhang et al, 2023).…”

Raptorial appendages of the Cambrian apex predatorAnomalocaris canadensisare built for soft prey and speed

“…Many radiodonts possess frontal appendages that are considered to have been raptorial and able to capture, manipulate and perhaps even masticate prey, before passing food items to the mouth for further processing [ 6 , 17 – 22 ]. In this context, select radiodonts are hypothesized to have been capable of shell-crushing (durophagous) predation [ 21 – 23 ], but there is still uncertainty as to whether breaking biomineralized prey was achievable using the frontal appendages, paired gnathobase-like structures affiliated with segments transitional between the head and trunk, the oral cone, or a combination of these, depending on the taxon [ 5 , 6 , 24 – 26 ].…”