The Ediacaran frondose fossilArboreafrom the Shibantan limestone of South China

Abstract

Bituminous limestone of the Ediacaran Shibantan Member of the Dengying Formation (551–539 Ma) in the Yangtze Gorges area contains a rare carbonate-hosted Ediacara-type macrofossil assemblage. This assemblage is dominated by the tubular fossil Wutubus Chen et al., 2014 and discoidal fossils, e.g., Hiemalora Fedonkin, 1982 and Aspidella Billings, 1872, but frondose organisms such as Charnia Ford, 1958, Rangea Gürich, 1929, and Arborea Glaessner and Wade, 1966 are also present. Herein, we report four species of Arborea from the Shibantan assemblage, including the type species Arborea arborea (Glaessner in Glaessner and Daily, 1959) Glaessner and Wade, 1966, Arborea denticulata new species, and two unnamed species, Arborea sp. A and Arborea sp. B. Arborea arborea is the most abundant frond in the Shibantan assemblage. Arborea denticulata n. sp. resembles Arborea arborea in general morphology but differs in its fewer primary branches and lower length/width ratio of primary branches. Arborea sp. A and Arborea sp. B are fronds with a Hiemalora-type basal attachment. Sealing by microbial mats and authigenic cementation may have played an important role in the preservation of Arborea in the Shibantan assemblage. The Shibantan material of Arborea extends the stratigraphic, ecological, and taphonomic ranges of this genus. UUID: http://zoobank.org/554f21da-5f09-4891-9deb-cbc00c41e5f1

Following the logic behind biological interpretations of the Ediacaran biotas

“…The original example of Charnia was rescued by Germs (Germs, 1973), who named it Glaessnerina, now a junior synonym of Charnia. Then in 1978, Jenkins & Gehling (1978) synonymized Arborea with Charniodiscus and she remained in limbo until resurrected from obscurity (Laflamme et al 2018;Wang et al 2020). All of this equivocation argues for a biological relationship between Charnia and Arborea that is significant at the scale of this review.…”

Charniodiscus and Arborea Are Separate Genera Within the Arboreomorpha: Using the Holotype of C. concentricus to Resolve a Taphonomic/Taxonomic Tangle

“…Throughout the ∼35 My of evolutionary history of the Ediacaran biota we observe a contrast between highly unique morphological disparity (Shen et al, 2008) and low taxonomic diversity (Waggoner, 2003). This has led to the creation of numerous monospecific genera, a lack of unified consensus regarding higher taxonomic ranks (Xiao and Laflamme, 2009), and genus and clade-level taxonomic inconsistencies (Brasier and Antcliffe, 2009;Liu et al, 2015;Laflamme et al, 2018;Wang et al, 2020).…”

“…In the light of our work there are several bifoliate planar arboreomorphs that require further taxonomic revision, including: 1) C. longus Glaessner and Wade, 1966 (formerly Rangea longa and Glaessnerina longa;Fedonkin et al, 2007), an elongate and lanceolate frond bearing at least 40 primary branches and uniform secondary subdivisions without a preserved stem or basal disc (Glaessner and Wade, 1966;Laflamme et al, 2004;Wang et al, 2020). The branching is clearly Arborea-like and there appears to be a prominent backing sheet (Figure 2D), indicating that it should likely be considered as Arborea longa.…”

“…The Newfoundland species of Charniodiscus have remained within the genus, despite the inferred multifoliate nature of the type species (Laflamme and Narbonne, 2008), but have also been considered to be separate from Arborea based on branching criteria of Brasier et al (2012). The need to unravel this taphonomic, and taxonomic, tangle has been mentioned in the literature by numerous authors (e.g., Brasier and Antcliffe, 2009;Liu et al, 2015;Laflamme et al, 2018;Wang et al, 2020) but remains unresolved.…”

“…All other taxa hitherto attributed to Charniodiscus (C. arboreus, C. longus, C. oppositus, and C. spinosus) should likely be considered to be species of Arborea but require further study and comparison with the type species (cf. Laflamme et al, 2018;Wang et al, 2020). The branches of C. concentricus are considered to be homologous with the pea-podlike units of Arborea (cf.…”