The earliest sponge spicule tufts from the Cambrian Lower Yanjiahe Formation, Three Gorges area, South China
(2025) In Palaeoworld 34(6).- Abstract
As phylogenetically basal metazoans, sponges (phylum Porifera) provide crucial insights into the origins of animal biomineralization and early body plan innovation. However, articulated sponge fossils remain exceptionally rare in Ediacaran–Cambrian transition strata, with most records limited to isolated spicules or ambiguous biomineralized structures. This study reports siliceous and phosphatically preserved sponge spicule tufts from the lower Yanjiahe Formation (∼535 Ma, Fortunian Stage) at the Muyangxi section (eastern Three Gorges area, South China). Dominated by monaxons, with co-occurring pentactine spicules, two morphotypes are distinguished: Type 1 tufts comprise slender, hollow monaxons (mean value of the maximum width: ∼15.9... (More)
As phylogenetically basal metazoans, sponges (phylum Porifera) provide crucial insights into the origins of animal biomineralization and early body plan innovation. However, articulated sponge fossils remain exceptionally rare in Ediacaran–Cambrian transition strata, with most records limited to isolated spicules or ambiguous biomineralized structures. This study reports siliceous and phosphatically preserved sponge spicule tufts from the lower Yanjiahe Formation (∼535 Ma, Fortunian Stage) at the Muyangxi section (eastern Three Gorges area, South China). Dominated by monaxons, with co-occurring pentactine spicules, two morphotypes are distinguished: Type 1 tufts comprise slender, hollow monaxons (mean value of the maximum width: ∼15.9 µm, n = 37) with uniform near-parallel alignment, while Type 2 tufts consist of sturdier phosphatized monaxons (mean value of the maximum width: ∼91.1 µm, n = 135) arranged as subparallel bundles, slightly radially oriented arrangements, and sometimes semi-randomly in single layers, occasionally with perpendicular alignments to the adjacent layers. Small curved oxeas in the Type 2 tufts suggest incipient hierarchical organization. Although fragmentary preservation limits taxonomic resolution, these tufts likely represent the earliest unequivocal biomineralized sponges, potentially corresponding to stem-group Demospongiae and/or Hexactinellida (Silicea). In combination with the previous evidences found from the Ediacaran–Cambrian transition, we hypothesize that early sponge biomineralization was likely monaxon-dominated, with hexactines arising via axial fusion or increased axis number, culminating in hexactinellid diversification by Terreneuvian Stage 2. Integrated with Small Shelly Fossil Zone 1 biochronology, our findings indicate rapid pre-Fortunian to Fortunian-stage spicule enlargement (≤ 200 μm to ≥ 500 μm) and architectural complexification, aligning with early Cambrian ecological escalation. Alternatively, it is possible that the divergence between Hexactinellida and Demospongiae may predate biomineralization, as their last common ancestor may have lacked siliceous spicules. The Yanjiahe spicules illuminate a critical prelude to the Cambrian sponge explosion, bridging Ediacaran soft-bodied ancestors and later diverse, mineralized clades.
(Less)
- author
- organization
- publishing date
- 2025-12
- type
- Contribution to journal
- publication status
- published
- subject
- keywords
- Cambrian, phosphate, silica, spicule tufts, Yanjiahe Formation
- in
- Palaeoworld
- volume
- 34
- issue
- 6
- article number
- 200995
- publisher
- Elsevier
- external identifiers
-
- scopus:105020977371
- ISSN
- 1871-174X
- DOI
- 10.1016/j.palwor.2025.200995
- language
- English
- LU publication?
- yes
- id
- daca9013-9d30-497c-b288-4965e287237c
- date added to LUP
- 2025-12-09 13:16:13
- date last changed
- 2025-12-10 08:43:49
@article{daca9013-9d30-497c-b288-4965e287237c,
abstract = {{<p>As phylogenetically basal metazoans, sponges (phylum Porifera) provide crucial insights into the origins of animal biomineralization and early body plan innovation. However, articulated sponge fossils remain exceptionally rare in Ediacaran–Cambrian transition strata, with most records limited to isolated spicules or ambiguous biomineralized structures. This study reports siliceous and phosphatically preserved sponge spicule tufts from the lower Yanjiahe Formation (∼535 Ma, Fortunian Stage) at the Muyangxi section (eastern Three Gorges area, South China). Dominated by monaxons, with co-occurring pentactine spicules, two morphotypes are distinguished: Type 1 tufts comprise slender, hollow monaxons (mean value of the maximum width: ∼15.9 µm, n = 37) with uniform near-parallel alignment, while Type 2 tufts consist of sturdier phosphatized monaxons (mean value of the maximum width: ∼91.1 µm, n = 135) arranged as subparallel bundles, slightly radially oriented arrangements, and sometimes semi-randomly in single layers, occasionally with perpendicular alignments to the adjacent layers. Small curved oxeas in the Type 2 tufts suggest incipient hierarchical organization. Although fragmentary preservation limits taxonomic resolution, these tufts likely represent the earliest unequivocal biomineralized sponges, potentially corresponding to stem-group Demospongiae and/or Hexactinellida (Silicea). In combination with the previous evidences found from the Ediacaran–Cambrian transition, we hypothesize that early sponge biomineralization was likely monaxon-dominated, with hexactines arising via axial fusion or increased axis number, culminating in hexactinellid diversification by Terreneuvian Stage 2. Integrated with Small Shelly Fossil Zone 1 biochronology, our findings indicate rapid pre-Fortunian to Fortunian-stage spicule enlargement (≤ 200 μm to ≥ 500 μm) and architectural complexification, aligning with early Cambrian ecological escalation. Alternatively, it is possible that the divergence between Hexactinellida and Demospongiae may predate biomineralization, as their last common ancestor may have lacked siliceous spicules. The Yanjiahe spicules illuminate a critical prelude to the Cambrian sponge explosion, bridging Ediacaran soft-bodied ancestors and later diverse, mineralized clades.</p>}},
author = {{Zhang, Lei and Wu, Ying and Zhai, Fan and Duan, Chen Zhang and Fu, Shan Shan and Chang, Shan and Ye, Yan and Chen, Can and Wang, Xia and Lang, Xian Guo and Feng, Qing Lai and Forel, Marie Béatrice}},
issn = {{1871-174X}},
keywords = {{Cambrian; phosphate; silica; spicule tufts; Yanjiahe Formation}},
language = {{eng}},
number = {{6}},
publisher = {{Elsevier}},
series = {{Palaeoworld}},
title = {{The earliest sponge spicule tufts from the Cambrian Lower Yanjiahe Formation, Three Gorges area, South China}},
url = {{http://dx.doi.org/10.1016/j.palwor.2025.200995}},
doi = {{10.1016/j.palwor.2025.200995}},
volume = {{34}},
year = {{2025}},
}