When paleontologists picture the earliest animals, they tend to imagine something with at least a rudimentary skeleton: a lattice of glassy needles, perhaps, or a mesh of calcium carbonate. But a fossil sponge pulled from late Ediacaran rocks in southern China is challenging that assumption. The organism, called Helicolocellus cantori, lived roughly 551 to 539 million years ago and appears to have been completely soft, with no mineralized skeleton whatsoever. Paired with a sweeping new evolutionary analysis published in June 2026, the discovery suggests that the very first animals on Earth were boneless, spineless, and skeletonless in the most literal sense, and that hard structures evolved independently in different sponge lineages much later.
A sponge with no spicules
Sponges alive today build their bodies around tiny structural elements called spicules, stiff rods made of silica or calcium carbonate that interlock to form a scaffold. Glass sponges, the group known as Hexactinellida, are famous for their intricate silica skeletons, some of which inspired 19th-century architects. So when a team led by Xiaopeng Wang described Helicolocellus cantori in Nature, the specimen stood out immediately. Recovered from the Dengying Formation in South China, it is a large, stalked organism with a body plan consistent with sponges, yet it preserves no trace of mineral spicules. Bayesian phylogenetic analysis places it within the crown group of Hexactinellida, meaning it sits among the ancestors and relatives of modern glass sponges, not on some distant, ambiguous branch of the tree of life.
That placement is striking. If Helicolocellus really is a glass sponge relative, then the iconic silica skeleton that defines the group today was absent in at least some of its earliest members. The organism apparently held itself together with organic fibers alone, a scaffold that would have decayed rapidly after death and left almost nothing for the fossil record to capture.
A broader pattern across all sponges
The fossil alone would be noteworthy. But a second study, published in Science Advances by a team including Maria Rossi, Ana Riesgo, Joseph Keating, and Martin Dohrmann, scales the question up to the entire phylum Porifera. Using a dated molecular phylogeny and model-based ancestral-state reconstruction for skeletal traits, the researchers concluded that the common ancestor of all living sponges was soft-bodied. Mineralized skeletons, they found, evolved independently multiple times in separate sponge lineages rather than arising once and being inherited by all descendants.
Their molecular clock estimates place the origin of sponges at roughly 600 to 615 million years ago, deep in the Precambrian and tens of millions of years before the oldest unambiguous sponge spicules appear in rock. That gap has long puzzled researchers. If sponges are as ancient as DNA evidence implies, where are the fossils? The new answer: the earliest sponges had nothing hard to fossilize.
Solving the ‘missing fossil’ problem
The two studies reinforce each other in a way that neither could achieve alone. Helicolocellus provides a physical specimen of a skeleton-free sponge from the Ediacaran period, the geological interval just before the Cambrian explosion of animal diversity. The Science Advances phylogeny provides the statistical framework showing that such a body plan was likely the ancestral condition for all sponges, not an oddity confined to one lineage.
Together, they offer a coherent explanation for one of paleontology’s most persistent gaps. If early sponges were entirely soft, they would have been nearly invisible in the geological record. Only when lineages independently acquired mineralized spicules, likely in response to shifting ocean chemistry and ecological pressures near the Precambrian-Cambrian boundary, would sponges have begun leaving durable fossils in any numbers.
Supporting evidence comes from Cambrian-age material as well. Specimens of Vasispongia delicata, described in a 2019 Nature Communications study, show that even some sponges living well into the Cambrian had only weakly biomineralized spicules or entirely organic skeletal components. These fragile structures degrade quickly after death, dramatically reducing fossilization potential. The finding bridges the gap between the fully soft Ediacaran forms and the robustly mineralized sponges that dominate later fossil assemblages, suggesting a prolonged interval during which sponge skeletons were patchy, fragile, or absent.
What ocean chemistry has to do with it
Geobiological research on Precambrian oceans adds another layer. Studies of silica cycling and ocean oxygenation near the Precambrian-Cambrian transition show that seawater chemistry was changing dramatically during the window when sponge mineralization appears to have arisen. Dissolved silica concentrations, oxygen levels, and nutrient availability were all in flux, creating conditions that may have favored organisms capable of building mineral skeletons.
In that context, the independent emergence of biomineralized skeletons in multiple sponge clades looks less like a coincidence and more like parallel responses to the same environmental pressures. The new fossil and phylogenetic results fit this picture by placing soft-bodied sponges at the root of the animal tree, with mineralization as a later, environmentally driven development rather than a single, once-and-for-all innovation.
Where the debate stands
None of this is settled. The phylogenetic placement of Helicolocellus rests on Bayesian analysis of morphological characters, a method sensitive to which traits are coded and how character models are specified. Alternative analytical approaches, different outgroup choices, or revised interpretations of key anatomical features could shift the fossil’s position on the sponge family tree. If it turns out to sit on a more distant stem lineage rather than within the crown group of glass sponges, the implications for skeletal evolution would change.
Older sponge fossil claims, some reaching far beyond 550 million years, have a long and contentious history. Purported sponge spicules from the Ediacaran Doushantuo Formation, for example, have been scrutinized with nanoscale analytical techniques, and some researchers argue those structures can be explained as abiotic mineral growths or microbial precipitates rather than genuine sponge remains. Diagnostic criteria for identifying early sponges remain actively debated.
The soft-body hypothesis also creates a new problem even as it solves an old one. If the first sponges lacked mineralized skeletons, paleontologists must rely on subtle impressions of soft tissue, organic films, or indirect geochemical signatures to identify them, all of which are far more ambiguous than a three-dimensional spicule array. Some Ediacaran fossils currently classified as “problematic” organisms might eventually be reclassified as sponges, but the risk of over-interpretation also rises when clear skeletal markers are absent.
The molecular clock dates of 600 to 615 million years carry their own uncertainties around substitution rates, gene sampling, and fossil calibration points. Different datasets or clock models can shift origin estimates by tens of millions of years. And no physical specimen yet captures the transition from organic to mineralized skeleton in progress, such as a sponge with partially mineralized spicules from the Ediacaran interval.
There is also the broader question of where sponges sit relative to other early animal groups. The long-running debate over whether sponges or comb jellies (ctenophores) represent the earliest-diverging animal lineage remains unresolved, and the answer affects how scientists interpret the ancestral animal body plan. If ctenophores diverged first, the implications of a soft-bodied sponge ancestor would be somewhat different than if sponges hold that position.
What one fossil can and cannot tell us
A single fossil taxon, however well preserved, cannot represent the full diversity of early sponges. It is possible that some of Helicolocellus‘s contemporaries experimented with incipient mineralization or alternative skeletal strategies that simply have not been found. Until a wider range of Ediacaran sponge fossils is discovered, inferences about the “typical” early sponge will remain provisional.
Still, the combination of a well-dated, skeleton-free sponge fossil and a global phylogenetic analysis of sponge evolution has shifted the balance of evidence. The most parsimonious reading of the current data is that the first animals were soft, fragile, and largely invisible in the geological record they helped inaugurate. Future discoveries, whether new fossils capturing intermediate skeletal stages, refined molecular clocks, or improved criteria for recognizing ancient sponge remains, will test how durable that picture turns out to be. For now, the rocks in southern China have offered a rare glimpse of a world before bones, before shells, before spicules: a world where the earliest animals held together with nothing more than organic fiber and, presumably, sheer evolutionary tenacity.
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*This article was researched with the help of AI, with human editors creating the final content.
