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Discovery of a Late-Ediacaran Crown-Group Sponge Fossil Challenges the Conventional View of Sponge Evolution


Core Concepts
The discovery of the late-Ediacaran fossil Helicolocellus cantori, a large, stemmed benthic organism with an organic skeleton similar to hexactinellid sponges, challenges the prevailing view that sponge fossils only appear in the Cambrian period and suggests sponges diverged and existed in the Precambrian as non-biomineralizing animals.
Abstract
The content describes the discovery of a late-Ediacaran fossil, Helicolocellus cantori, from the Dengying Formation in South China, dated around 551-539 million years ago. This fossil is reconstructed as a large, stemmed benthic organism with a goblet-shaped body over 0.4 m in height, and a body wall consisting of at least three orders of nested grids defined by quadrate fields, resembling a Cantor dust fractal pattern. The lattice structure is interpreted as an organic skeleton comprising orthogonally arranged cruciform elements, architecturally similar to some hexactinellid sponges, although the latter are built with biomineralized spicules. A Bayesian phylogenetic analysis resolves H. cantori as a crown-group sponge related to the Hexactinellida. This discovery challenges the prevailing view that sponge fossils only appear in the Cambrian period, as it confirms that sponges diverged and existed in the Precambrian as non-biomineralizing animals with an organic skeleton. The authors also question the validity of biomineralized spicules as a necessary criterion for the identification of Precambrian sponge fossils, considering that siliceous biomineralization may have evolved independently among sponge classes.
Stats
The fossil Helicolocellus cantori is reconstructed as a large, stemmed benthic organism with a goblet-shaped body more than 0.4 m in height. The body wall of the fossil consists of at least three orders of nested grids defined by quadrate fields, resembling a Cantor dust fractal pattern.
Quotes
"Sponges are the most basal metazoan phylum1 and may have played important roles in modulating the redox architecture of Neoproterozoic oceans2." "Although molecular clocks predict that sponges diverged in the Neoproterozoic era3,4, their fossils have not been unequivocally demonstrated before the Cambrian period5,6,7,8, possibly because Precambrian sponges were aspiculate and non-biomineralized9."

Key Insights Distilled From

by Xiaopeng Wan... at www.nature.com 06-05-2024

https://www.nature.com/articles/s41586-024-07520-y
A late-Ediacaran crown-group sponge animal - Nature

Deeper Inquiries

How might the discovery of Helicolocellus cantori impact our understanding of the evolutionary history and ecological roles of sponges in the Neoproterozoic era?

The discovery of Helicolocellus cantori challenges previous assumptions about the timing of sponge evolution, suggesting that sponges diverged and existed in the Precambrian as non-biomineralizing organisms. This finding expands our understanding of the diversity and ecological roles of sponges in the Neoproterozoic era, indicating that these basal metazoans were present and potentially played significant roles in modulating the redox architecture of ancient oceans. By demonstrating the existence of non-biomineralized sponge fossils in the late-Ediacaran period, the discovery of H. cantori highlights the need to reconsider the criteria used to identify Precambrian sponge fossils and sheds light on the evolutionary history of these foundational organisms.

What other types of non-biomineralized sponge fossils might be present in the Precambrian fossil record, and how could researchers identify them?

In addition to Helicolocellus cantori, other types of non-biomineralized sponge fossils may be present in the Precambrian fossil record. These could include aspiculate sponges with organic skeletons similar to H. cantori, as well as other forms that lack biomineralized spicules. Researchers could identify these fossils by examining the morphological characteristics of the specimens, such as the presence of intricate lattice structures, nested grids, or other unique patterns that suggest an organic skeletal framework. Additionally, phylogenetic analyses, similar to the Bayesian analysis conducted on H. cantori, could help place these fossils within the sponge evolutionary tree and confirm their identity as non-biomineralized sponge organisms from the Precambrian era.

What insights could the fractal-like skeletal structure of Helicolocellus cantori provide into the developmental and evolutionary processes that gave rise to complex sponge body plans?

The fractal-like skeletal structure of Helicolocellus cantori offers valuable insights into the developmental and evolutionary processes that led to the formation of complex sponge body plans. The presence of nested grids and quadrate fields in the body wall of H. cantori suggests a high level of structural organization and symmetry, indicating sophisticated developmental mechanisms at play during its growth. By resembling a Cantor dust fractal pattern, the lattice structure of H. cantori hints at self-similarity and iterative growth processes that may have contributed to the evolution of larger and more intricate sponge body plans over time. Studying the developmental genetics and regulatory pathways involved in forming such fractal-like structures in sponges like H. cantori could provide valuable insights into the genetic basis of sponge body plan complexity and the evolutionary transitions that shaped early metazoan diversity.
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