A late-Ediacaran crown-group sponge animal

Area of Science:

• Paleontology
• Evolutionary Biology
• Geology

Background:

• Sponges are basal metazoans crucial for understanding early animal evolution.
• Molecular clocks suggest sponge divergence in the Neoproterozoic, but fossil evidence is scarce before the Cambrian.
• Precambrian sponges may have been non-biomineralized, complicating fossil identification.

Purpose of the Study:

• To describe a new fossil organism, Helicolocellus cantori, from the late Ediacaran period.
• To investigate the early evolution and skeletal structures of Precambrian sponges.
• To re-evaluate the criteria for identifying Precambrian sponge fossils.

Main Methods:

• Fossil description and reconstruction of Helicolocellus cantori from the Dengying Formation.
• Analysis of the fossil's unique grid-like organic skeleton.
• Bayesian phylogenetic analysis to determine its evolutionary relationships.

Main Results:

• Discovery of Helicolocellus cantori, a large, stemmed, goblet-shaped organism with a fractal-patterned organic skeleton.
• Phylogenetic analysis places H. cantori within the crown-group sponges, related to Hexactinellida.
• The fossil confirms the existence of non-biomineralizing sponges with organic skeletons in the Precambrian.

Conclusions:

• Sponges existed in the Precambrian with organic skeletons, predating biomineralization.
• Biomineralized spicules may not be a universal or necessary characteristic for identifying early sponge fossils.
• This discovery impacts our understanding of early metazoan evolution and the criteria for fossil identification.