266-1 Redescription of China’s first named Ediacara-type macrofossil

Session: The Neoproterozoic Earth and Life Co-evolution (Posters)

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Abstract:

Paracharnia dengyingensis, an elongated, unipolar frond with a seemingly wide stalk and bifoliate leaf-like petalodium tapering towards its bent apex, was discovered in 1978 in the organic-rich limestone Shibantan Member (~551–543 Ma) of the Dengying Formation in the Yangtze Gorges area of South China. This discovery represented the first Ediacara-type macrofossil found in China. Since its initial description (1) and subsequent re-examination (2), extensive research has been conducted to define taxonomic characters used to classify Ediacaran fronds. In addition to new nomenclature, it is now understood that Ediacaran fronds display four distinct branching arrangements (Arborea-, Charnia-, Rangea-, andSwartpuntia-type) and grouping these organisms accordingly enhances understanding of phylogenetic relationships. In light of these advancements, we reanalyzed Paracharnia dengyingensis. Paracharnia dengyingensis is at least 22 cm long and 2 cm wide at its maximum width. It has parallel, possibly furled primary branches that diverge from the straight portion of the stalk at angles generally increasing from the base to the apex of the petalodium (~30°–80°). The specimenhas at least 64 identifiable primary branches attached on both sides of the stalk and is inferred to have more than 40 primary branches on each foliate. A basal disc and stem are not observed because of taphonomic loss or primary morphology. Putative second-order branches are poorly preserved, and if present, diverge ~90° from the axis of the primary branch. Tertiary branching is not observed. Recrystallization of the carbonate cement, which is responsible for fossil preservation, may have obscured these finer details. Based on these angular branching relationships, Paracharnia dengyingensis is inferred to demonstrate Arborea-type branching. The high number of primary branches and elongate petalodium distinguishes Paracharnia dengyingensis from known Arborea in South China and is most comparable with Trepassia (rangeomorph) and Akrophyllas (arboreomorph). This implies that the elongated, narrow petalodium of Paracharnia dengyingensis is a convergent morphology observed across different ‘clades’ of Ediacaran fronds. Redescription of Paracharnia dengyingensis using updated taxonomic characters ensures this taxon can be properly incorporated into the global dataset of Ediacaran fronds and informs ongoing discussion on their taxonomy.

1. Q Ding, Y Chen. Earth Science (Journal of China University of Geoscience), 15, 53-57 (1981).

2. S Weiguo. Precambrian Research, 31, 361-375 (1986). 

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-5157

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