Collagen is the structural backbone of animal bodies. It weaves through skin, muscle, organs and connective tissue, giving even the squishiest organisms a measure of internal scaffolding. In the absence of enzymes capable of cutting it apart, collagen is remarkably stubborn. Philip Vixseboxse, lead author of the study, who completed the work as a PhD candidate in Cambridge’s Department of Earth Sciences, compares it to modern plastic: a biopolymer that simply sits there until something evolves the biochemical machinery to digest it. Once an organism dies, however, and collagen-degrading enzymes known as collagenases are present, that scaffolding can be dismantled rapidly, collapsing the tissues long before sediment can entomb them in a form capable of surviving hundreds of millions of years.

The contrast between eras is what makes the new findings so compelling. During the late Ediacaran Period, between roughly 579 and 539 million years ago, Earth hosted its first known communities of complex animal life. None of these organisms possessed hard parts, yet at sites around the world their fossils are preserved with extraordinary fidelity — in some places entire ecosystems, complete with the soft anatomy of animals that would otherwise have left nothing behind. For decades, researchers have wrestled with how this was possible. Proposed explanations have included unusual ocean chemistry, distinctive tissue compositions in Ediacaran animals, and the presence of a pervasive microbial mat or slime layer that blanketed the seafloor and sealed remains beneath it. Each of these mechanisms can account for preservation at particular localities, but none of them works universally, and the debate has remained unresolved.

To test whether biology itself might hold the answer, Vixseboxse and his colleagues turned to genomics. They traced the evolutionary history of collagenase genes across 700 bacterial genomes and mapped those genes onto a time-dated tree of life, allowing them to reconstruct when and in which microbial groups the ability to degrade collagen first appeared and then spread. The results revealed that collagenases are far older than animals themselves. Crucially, however, the earliest collagenases belonged exclusively to anaerobic microbes — organisms that cannot tolerate oxygen. In the oxygenated waters of the Ediacaran oceans, that limitation mattered enormously.

The logic of the preservation window follows directly from that biochemical constraint. When an Ediacaran animal died and sank into the sediment, aerobic decay processes would consume the oxygen in the surrounding sediments relatively quickly. Once that oxygen was gone, the anaerobic collagen-degrading microbes could go to work — but only slowly, and only after a substantial delay. In the interim, the animal’s collagen-rich tissues remained intact, giving mineralisation and impression-forming processes time to operate. In effect, the microbial community of the Ediacaran seafloor imposed a built-in lag between death and destruction, and that lag was exactly what fragile, soft-bodied animals needed to enter the fossil record. The ‘bags of goo’ of the Ediacaran were, paradoxically, protected by the very limitations of the microbes that would eventually consume them.

That protection did not last. As the team’s genomic timeline shows, around the transition between the Ediacaran and Cambrian Periods, collagenase genes began to spread far more widely through the microbial world. Through horizontal gene transfer, the enzymes moved into a much broader range of bacterial groups, including aerobic bacteria — the oxygen-using microbes that drive much of the decay we observe today. Once collagen degradation became possible in oxygenated environments, the protective lag disappeared. Tissues could begin breaking down immediately after death, in oxygen-rich settings, dramatically shortening the window in which fossilisation could occur. This shift, the researchers note, coincides with a pronounced decline in the abundance and quality of soft-tissue fossils in the rock record.

‘Around this critical time where these soft-bodied animals stopped fossilising, we start seeing the appearance of collagenases in aerobic bacteria, meaning the ability to break down collagen-bearing tissues could start to spread into new environments as animal diversity accelerated,’ said Vixseboxse. ‘Now that collagen could be degraded, you needed ever-faster fossilisation processes to outpace decay, which is likely why we start to see a big drop in the abundance and quality of the fossil record, in terms of the preservation of soft tissue.’ The timing is significant because the Cambrian was also the period in which animal diversity exploded, filling the oceans with new body plans and, implicitly, with vastly more collagen — a fresh and abundant food resource for any microbe equipped to exploit it.

The new model does not mean that soft tissues vanished from the fossil record entirely after the Ediacaran. Exceptional circumstances can still deliver exquisite preservation in younger rocks, and palaeontologists have documented many such Lagerstätten, from the Burgess Shale to Chengjiang. The key variable, according to the study, is speed. An animal buried almost instantaneously — beneath an avalanche of sediment triggered by a storm or a slump, for example — can be sealed away from oxygen and decay agents before its collagen is dismantled. But such rapid burial is inherently rare, which is why soft-tissue fossils from the Cambrian onward are celebrated exceptions rather than the norm. The baseline probability of preservation collapsed once aerobic collagen degradation became widespread.

‘These results suggest there may be an overarching biological mechanism that has shaped the fossil record of soft tissues across Earth’s history,’ said co-author Professor Alex Liu, also of the Cambridge Department of Earth Sciences. ‘The acquisition of key enzymes by microbes to exploit a growing food resource may have decreased the preservation potential of soft tissues.’ Framed this way, the gaps in the fossil record are not simply an artefact of incomplete sampling or unlucky geology. They reflect an evolutionary arms race of sorts: as animals diversified and flooded the environment with collagen, microbes evolved the tools to exploit it, and in doing so they rewrote the rules of what could survive the passage of deep time.

The study, published in the journal Current Biology, also carries a provocative modern echo. Vixseboxse points out that plastic behaves in the environment much as collagen once did — a persistent biopolymer that accumulates because nothing has yet evolved to break it down efficiently. ‘Bacteria had no reason to efficiently degrade collagen when it didn’t exist,’ he said. ‘But once collagen became more abundant, and provided a new food source for these microbes, collagenases proliferated. Perhaps someday, microbes will exploit similar enzymes to break down the increasing abundance of plastic polymers we are putting into the environment, but that will be long after we’re gone.’ The research was supported in part by the Leverhulme Trust, the Natural Environment Research Council and the Biotechnology and Biological Sciences Research Council, part of UK Research and Innovation. If the analogy holds, the same evolutionary logic that erased the soft-bodied Ediacaran world may one day reshape the Anthropocene’s most durable litter — a reminder that in biology, no polymer stays indigestible forever.

Subject of Research: Evolution of microbial collagenase enzymes and its impact on the preservation of soft-bodied animals in the fossil record

Article Title: Rise of collagen-eating microbes may help explain gaps in the fossil record

Article References: Rise of collagen-eating microbes may help explain gaps in the fossil record. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: fossil record, collagen, collagenase, Ediacaran, Cambrian, soft-tissue preservation, microbial evolution, palaeontology, taphonomy, bacteria, University of Cambridge, Current Biology

The West African Craton is one of Earth’s great stable blocks of continental crust, and its northern margin has long been a battleground for geologists trying to understand how it was assembled into Gondwana. The Anti-Atlas belt preserves two major orogenic cycles: the roughly 2.2-billion-year-old Eburnean Orogeny in the west, and the Neoproterozoic Pan-African Orogeny, which culminated around 650 million years ago with the accretion of oceanic arc and ophiolite complexes such as those at Bou Azzer and Sirwa. A major structure called the Anti-Atlas Major Fault has traditionally been drawn as the boundary between the ancient Eburnean basement and the younger Pan-African terranes. Whether Paleoproterozoic crust extends north of that fault, however, has remained one of the most contested questions in the region, and it is precisely here that the new detrital zircon data deliver their most striking result.

The team analyzed a fine- to medium-grained greenish sandstone collected near the entrance of the Zgounder silver mine, part of the Imghi Formation of the Saghro Group. This unit consists of thick-bedded greywackes and graded turbidites, the classic deposits of deep-water sediment gravity flows. Of 138 laser-ablation analyses on 93 zircon grains, 90 were concordant, and the age spectrum turned out to be remarkably narrow. The youngest coherent cluster of grains yielded a maximum depositional age of 2025 million years, while the overall distribution is dominated by a single sharp peak at about 2100 million years, with one lone grain as old as 3700 million years. Crucially, not a single zircon younger than 1600 million years was found, despite the fact that Pan-African igneous rocks between 883 and 640 million years old are abundant in the surrounding Sirwa inlier and are commonly reported in Saghro Group sediments elsewhere.

That absence is the key. The narrow gap between the 2100-million-year peak and the 2025-million-year maximum depositional age suggests that the sediments were dumped into a basin flanked by an uplifted, pristine block of Eburnean basement that acted as the exclusive sediment source. The basin received no volcanic ash or erosional debris from the Ediacaran magmatism that was raging elsewhere in the belt. In other words, the Saghro Group basin in the Sirwa area was walled by 2.1-billion-year-old continental crust. Because the number of grains analyzed is well above the thresholds normally considered adequate for provenance work, the authors argue the result is robust rather than a sampling artifact. The implication is that Paleoproterozoic crust of the West African Craton extends beneath the Sirwa massif and continues northward beyond the Anti-Atlas Major Fault, possibly as far as the South Atlas Fault, which would shift the location of the definitive craton-margin suture zone significantly to the north.

The magmatic rocks tell an equally compelling story, in two acts. The first act belongs to the Saghro Group, whose mafic volcanic and intrusive rocks, basalts, basaltic andesites, dolerites, and a gabbro from the Tittalt Formation, define a calc-alkaline suite with a within-plate geochemical signature. On normalized multi-element diagrams they show enrichment in large-ion lithophile elements such as cesium, rubidium, barium, and potassium relative to high-field-strength elements, together with the negative niobium-tantalum and titanium anomalies that are the classic fingerprint of subduction-zone influence. Yet tectonic discrimination diagrams place them in the fields of continental tholeiites adjacent to back-arc basin basalts. The combination points to an early Ediacaran extensional phase in which advanced lithospheric thinning allowed asthenospheric decompression melting of a sub-continental lithospheric mantle that had been chemically fertilized, or metasomatized, by an earlier Cryogenian subduction event.

Isotopes reinforce this picture of a young, mantle-dominated magma system. The Saghro Group samples yield strongly positive initial epsilon-neodymium values of +3.2 to +4.6, calculated at a reference age of 620 million years, with depleted-mantle model ages of 1.02 to 0.91 billion years. A binary mixing model, using a metasomatized mantle end-member and a Paleoproterozoic crustal end-member with an epsilon-neodymium of about -16, indicates that the Saghro magmas contain 88 to 92 percent mantle-derived material and only 8 to 12 percent crustal input. These are among the most juvenile signatures known from the Ediacaran of the Anti-Atlas, and they suggest the back-arc basin was opening above a mantle source that had been only lightly contaminated by older crust, consistent with the thinning lithosphere of a maturing basin behind the Cadomian subduction zone that fringed the Gondwanan margin.

The second act is the Ouarzazate Group, and it could hardly be more different. New U-Pb zircon ages of 575 plus or minus 3 million years for a rhyolitic dike and 564 plus or minus 2 million years for a granite intersected in a drill hole at 555 to 568 meters depth bracket roughly 11 million years of post-collisional magmatism. These ages match, within uncertainty, a suite of previously dated intrusions in the Sirwa massif, including the Askaoun granodiorite, the Tikhfist rhyolite, and the Imourkhssen granite, indicating a rapid succession of intrusive events. Geochemically, the Ouarzazate rocks form a high-K calc-alkaline to shoshonitic, felsic-to-intermediate series with silica contents reaching nearly 80 weight percent, pronounced negative europium anomalies, and strong depletion in strontium, phosphorus, niobium, tantalum, and titanium, the hallmarks of extensive plagioclase and accessory-mineral fractionation combined with a strongly crustal source.

The isotopic contrast between the two groups is stark. Ouarzazate Group rocks cluster near or below the chondritic reference line, with initial epsilon-neodymium values between -0.8 and +1.1 and model ages of 1.30 to 1.15 billion years, far older than their crystallization ages. The mixing model quantifies the shift: crustal contributions rise from about 15 percent in a granodiorite to 25 percent in a rhyolite. Without such contamination, a purely mantle-derived magma at 570 million years ago would be expected to show epsilon-neodymium values of +7 to +8, so the near-zero values represent a major isotopic pull from ancient basement. A single inherited zircon grain of 2156 plus or minus 54 million years in the granite provides direct physical evidence of that reworking, matching widespread Paleoproterozoic inheritance reported in Ouarzazate ignimbrites and granites across the Anti-Atlas.

Putting the pieces together, the authors propose a coherent geodynamic sequence. Around 630 to 600 million years ago, the Saghro Group sediments and their associated calc-alkaline mafic magmas accumulated in a back-arc basin whose shoulders were built of uplifted 2.1-billion-year-old Eburnean crust. As the basin matured, magmas progressively tapped deeper, less contaminated asthenospheric reservoirs, a transition mirrored by the rift-tholeiite, ocean-island-basalt, and mid-ocean-ridge-basalt signatures seen in basalts higher in the Saghro stratigraphy at Sidi Flah and Boumalne. Then, in the late Ediacaran, the tectonic regime flipped. Lithospheric delamination and possible slab break-off injected a thermal pulse into the lower continental crust, triggering widespread melting of both the crust and a subduction-modified lithospheric mantle. The result was a massive flare-up of silicic volcanism and plutonism, part of a Silicic Large Igneous Province recognized across the Anti-Atlas, whose A2-type granites and shoshonitic ignimbrites record post-collisional crustal collapse on the fractured, metacratonic margin of the craton.

Beyond rewriting the tectonic map of northwest Gondwana, the study has practical resonance. The Zgounder deposit, one of Morocco’s most important silver mines, sits within exactly this Ediacaran magmatic framework, and the same extensional structures that channeled deep-sourced magmas upward also focused mineralizing fluids. More broadly, the work demonstrates how a single handful of detrital zircons, when read carefully, can relocate a continental suture by hundreds of kilometers and reveal that the craton beneath modern Morocco is far more extensive than its surface outcrops suggest. As similar isotopic and geochronological toolkits are applied to other contested craton margins around the world, hidden blocks of ancient crust may well continue to surface from the sedimentary record itself.

Subject of Research: Petrogenesis and geodynamic setting of Ediacaran sedimentary and magmatic rocks in the Sirwa massif, Central Anti-Atlas, Morocco

Article Title: Petrogenesis and geodynamic setting of Ediacaran rocks from the Sirwa massif, Central Anti-Atlas of Morocco

Article References: Ben-Tami, A., Belkacim, S., El Kabouri, J., Baidada, B., Davies, J. H. F. L., Perrot, M. G., Bhilisse, M., Assalmi, M., Ferraq, M., & Bouabdellah, M. (2026). Petrogenesis and geodynamic setting of Ediacaran rocks from the Sirwa massif, Central Anti-Atlas of Morocco. Solid Earth, 17(9), 1063-1086. https://doi.org/10.5194/se-17-1063-2026

Image Credits: AI Generated

DOI: 10.5194/se-17-1063-2026

Keywords: Anti-Atlas, Morocco, Ediacaran, detrital zircons, U-Pb geochronology, West African Craton, Pan-African Orogeny, back-arc basin, post-collisional magmatism, Sm-Nd isotopes, Saghro Group, Ouarzazate Group

GRIND itself was born in 2014, when 44 scientists from 14 countries gathered at the British Geological Survey to design a core archive spanning the entire Neoproterozoic Era, from 1000 to 538.8 million years ago. The era witnessed extraordinary upheaval: a supercontinent broke apart and another assembled, marine oxygen climbed toward modern levels, the global carbon cycle swung through wild fluctuations, and ice sheets twice engulfed the planet during the Snowball Earth glaciations. Against that turbulent backdrop, the first animals emerged, marine planktonic algae rose to prominence, and biomineralization, the ability to build skeletons, became widespread. The International Continental Scientific Drilling Program accepted the proposal in 2018, dividing it into three phases: GRIND-TON for the Tonian, GRIND-CRY for the Cryogenian, and GRIND-ECT for the Ediacaran–Cambrian Transition. The team unanimously chose to begin with GRIND-ECT, targeting the interval that Darwin himself found so troubling that he called the sudden appearance of Cambrian fossils one of the gravest objections to his theory of evolution.

The scientific stakes are considerable. The appearance and diversification of animals between about 650 and 500 million years ago constitute one of the most profound episodes in the evolution of Earth’s ecosystems, yet the causes of the so-called long fuse leading to the Cambrian Explosion remain among science’s great unresolved challenges. GRIND-ECT is designed to answer several fundamental questions: What were the temporal and spatial patterns of marine oxygenation, and do they collectively represent a Neoproterozoic oxygenation event? What drove the large-amplitude carbon isotope excursions that mark Ediacaran and early Cambrian strata? How quickly did the Ediacaran biota appear, expand, and disappear? And is the Ediacaran–Cambrian boundary a synchronous worldwide biological event or a lengthy episode of progressive innovation? Answering these questions requires rock records with exceptional stratigraphic completeness, broad palaeogeographic distribution, and fine temporal resolution, which is precisely what the chosen drilling sites promised.

Three successions were identified as ideal targets: the Nama Group in Namibia, the Corumbá Group in Brazil, and the Yangtze Platform of South China. All preserve thick, laterally continuous sequences with minimal structural disturbance and, crucially, datable volcanic ash horizons that allow high-resolution correlation. The Namibian and Brazilian phases are now complete, while the Chinese phase, delayed by COVID-19 restrictions, began drilling in 2024. In Namibia, the contractor Günzel Drilling recovered more than 2379 metres of HQ-diameter core in six overlapping cores, achieving over 95 percent recovery while averaging 50 metres of core per day. The team used only re-circulated water as a lubricant, avoiding chemical drilling fluids that could contaminate geochemical analyses, and restored drill sites to exceptional environmental condition. In Brazil, the contractor Roquesonda drilled two cores totalling 306 metres with similarly high recovery. Boreholes were drilled perpendicular to bedding, so measured depth corresponds closely to true stratigraphic thickness.

The Namibian cores target the Kuibis and Schwarzrand sub-groups of the Nama Group, a mixed sandstone-shale-carbonate succession two to three kilometres thick deposited in a foreland basin that formed during the collision of the Congo, Rio de la Plata, and Kalahari cratons as Gondwana assembled. These strata, known since the early twentieth century, contain a rich record of Ediacaran life, including the tubular calcifying fossil Cloudina, related small shelly fossils, impressions of large soft-bodied organisms, and trace fossils ranging from simple burrows to complex networks that document the activities of some of the earliest mobile animals. The environments sampled span shorelines to deeper-marine ramps. Equally important for the project’s success was the geology itself: the strata in the Witpütz Sub-basin are flat-lying to gently dipping, with deformation limited to widely spaced sub-vertical normal faults that could be identified and avoided, and excellent surface outcrops adjacent to the drill sites allow the cores to be tied directly to mapped geological features.

The six Namibian cores form an overlapping stratigraphic ladder through the succession. Core 1G at Anib, 272.48 metres long, recovers the oldest strata, from the basal unconformity on the 1.3 to 1.0 billion-year-old Namaqua metamorphic complex up through fluvial sandstones and shallow-marine limestones bearing soft-bodied macrofossils and calcitized small shelly fauna. Core 1A at Tierkloof, at 563.78 metres the longest, samples the deeper-water shales and storm-influenced sandstones of the Nudaus Formation and Nasep Member, including pyritic black shales that may prove ideal for rhenium-osmium dating. Cores 1B, 1D, 1F, and 1H span the youngest units, the fossil-rich Huns and Spitskop members, whose limestones, microbialites, and interbedded volcanic tuffs hold the key to dating the Ediacaran–Cambrian boundary. The youngest dated tuff in the region has a uranium-lead zircon age of 538.57 million years, while the oldest known tuff in the wider basin dates to 547.36 million years, and tuffs recovered in the cores are expected to refine these age models considerably.

The carbon isotope story embedded in these carbonates is equally compelling. Late Ediacaran carbon isotope records show several globally recognized excursions, most notably the Basal Cambrian Excursion, in which the carbon isotope ratio of seawater plunges by roughly 5 to 10 per mil before recovering, coinciding with major biotic turnover just before the formally defined boundary at about 541 million years ago. Intriguingly, the lack of a clear BACE signal in the Schwarzrand Sub-group has led some researchers to suggest that the Ediacaran–Cambrian boundary may lie higher in the Nama succession than traditionally assumed. The continuous, unweathered core record now offers a means of building a finely resolved chemostratigraphy anchored by radiometric ages, testing whether these excursions are truly global signals or regional phenomena, and constraining the mass balance between organic productivity and carbon burial during a time of rising atmospheric oxygen.

In Brazil, the two cores drilled near Corumbá in Mato Grosso do Sul sample the Corumbá Group, a carbonate platform succession deposited along the southeastern margin of the Amazon Craton. The Tamengo Formation is South America’s premier Ediacaran fossil locality, hosting Cloudina lucianoi, the enigmatic Corumbella werneri, conulariids, macroalgae, and bilaterian trace fossils, while the overlying Guaicurus Formation contains vendotaenid fossils. Ash beds in the Tamengo Formation have yielded uranium-lead zircon ages of 542.37 and 541.85 million years, placing the unit firmly in the terminal Ediacaran, and its carbon isotope profile records the rising limb of the Shuram excursion. Core 3A at the Sobramil site, 183.1 metres long, captures microbialites, oncoids, and breccias of the Bocaina Formation before crossing an erosive boundary into the black shales and grainstones of the Tamengo. Core 3B at the Corcal Mine, 122.6 metres long, shows the same transition and ends in weathered siltstones of the Guaicurus Formation. Together the facies record a major change from a rimmed shelf to a distally steepened ramp, punctuated by storm-dominated deposition.

All cores were shipped to the Bundesanstalt für Geowissenschaften und Rohstoffe core archive in Berlin-Spandau, where they were split, scanned, and logged into the International Continental Scientific Drilling Program’s database. Under the GRIND agreement, split halves will eventually be returned to Namibia and Brazil for in-country training and study, with archive material also held at the Ministry of Mines in Windhoek and the Universidade de São Paulo. Three sampling parties have so far collected 2823 samples from the Namibian cores and 267 from the Brazilian ones, targeting an extraordinary analytical suite: stable isotopes of carbon, nitrogen, sulfur, strontium, uranium, calcium, boron, chromium, and other elements; organic and inorganic carbon contents; major, trace, and rare earth element geochemistry; iron and phosphorus speciation; uranium-lead and rhenium-osmium geochronology; palaeomagnetism; and micropalaeontology. The first characterization party alone involved 28 researchers and 2794 samples.

Early results are already reshaping understanding of the interval. Spectral analysis of magnetic susceptibility data from the lower Schwarzrand Sub-group has identified orbital cycles that allow sedimentation rates to be calculated, yielding an updated age-depth model that refines the timing of the earliest major radiation of bilaterian animals. Palaeomagnetic work has identified a primary magnetic component recording an unstable geomagnetic field at 540 million years ago, the youngest such evidence from the Ediacaran and the first from the Kalahari Craton. High-precision uranium-lead dating of tuffs has revealed a cryptic structural repetition in the Spitskop Member, sparking active debate about the chronostratigraphy of the terminal Ediacaran. Perhaps most significantly, current age models indicate exceptionally high sedimentation rates in the Schwarzrand Sub-group, producing an expanded Ediacaran–Cambrian succession that likely preserves a higher-resolution record of evolutionary change than is available anywhere else on Earth. As isotope geochemistry, geochronology, and facies analysis converge on these cores, GRIND-ECT is delivering the data needed to test, at last, what triggered the greatest biological revolution in Earth history, and the Berlin archive will serve as a legacy resource for decades to come.

Subject of Research: Scientific drilling of late Ediacaran rocks in Namibia and Brazil to reconstruct the environmental and biogeochemical context of early animal evolution across the Ediacaran–Cambrian transition

Article Title: GRIND-ECT: geological research through integrated Neoproterozoic drilling – Ediacaran–Cambrian transition

Article References: Rose, C. V., Kasemann, S. A., Macdonald, F. A., Mesli, M., Nduutepo, A., Trindade, R., Zhu, M., & Prave, A. R. (2026). GRIND-ECT: geological research through integrated Neoproterozoic drilling – Ediacaran–Cambrian transition. Scientific Drilling, 35(2), 171-192. https://doi.org/10.5194/sd-35-171-2026

Image Credits: AI Generated

DOI: 10.5194/sd-35-171-2026

Keywords: GRIND-ECT, Ediacaran, Cambrian Explosion, scientific drilling, Nama Group, Corumbá Group, Cloudina, Namibia, Brazil, chemostratigraphy, ICDP, early animal evolution

The mystery at the centre of the study is a familiar one to palaeontologists. Animals appear relatively suddenly in the fossil record just before the Cambrian Period, which ran from 539 to 487 million years ago, yet a growing body of indirect evidence suggests their evolutionary history began much earlier. Molecular clock analyses, which compare genetic differences between living species and work backwards using fossil dates as calibration points, have repeatedly hinted at a deep pre-Ediacaran origin. But many recent studies have constrained those estimates using a seemingly straightforward argument drawn from the fossil record itself, and it is precisely that argument which the new work dismantles.

The argument hinges on an exceptionally well-preserved fossil deposit in China known as the Weng’an Biota, found in rocks of Ediacaran age and dated to roughly 590 million years ago. The Weng’an Biota preserves microscopic organisms in extraordinary cellular detail, yet none of the fossils it contains can be definitively identified as animals. Researchers have therefore inferred that the first animals must have originated after Weng’an, reasoning that a deposit capable of preserving such delicate structures would certainly have captured animal embryos or larvae if animals existed at the time. In effect, Weng’an has been treated as a maximum age constraint, a hard ceiling on how old animals could possibly be.

The Oxford-led team, which included researchers from the University of California Berkeley, ETH Zürich and Yale University, tested that logic by surveying a younger deposit with comparable preservation quality: the Kheseen Biota of Mongolia. The Kheseen Biota is more than 40 million years younger than Weng’an, yet the two deposits share some species, and by the time Kheseen was laid down animal fossils were already known from sites elsewhere in the world, including Namibia and South China. The researchers examined more than 140 samples, some from previously undocumented localities, using scanning electron microscopy to resolve fine anatomical detail at the microscopic scale.

The results were striking. The Mongolian material yielded exquisite new microfossil species, including acritarchs, tiny spherical organisms adorned with spines and branching projections, as well as embryo-like fossils preserving internal cells. The quality of preservation rivals anything seen in the Ediacaran record. Yet despite this remarkable fidelity, not a single specimen could be confidently assigned to the animal kingdom. Animals were demonstrably alive when the Kheseen Biota formed, but they left no trace within it, a direct contradiction of the preservation-based reasoning applied to Weng’an.

Senior author Associate Professor Ross Anderson of the Museum of Natural History at Oxford University explained the significance of the finding. The Kheseen Biota, he said, breaks the argument that the exceptional microfossils of Weng’an mean animal fossils would have been seen in the assemblage had they existed at the time. The Kheseen microfossils are just as well-preserved, yet animals continue to be absent, despite the fact that they are known to have existed by that point. The most plausible explanation is that early animals lived in environments different from those that preserved the Kheseen fossils, or that the local chemical conditions after death simply failed to preserve animal remains.

With the Weng’an ceiling removed, the team rebuilt their molecular clock analyses using much older geological constraints. They turned to fossil-rich deposits dating from roughly 850 to 730 million years ago, including the Svanbergfjellet Formation in Norway, the Bitter Springs Group in Australia and the Chuar Group in Arizona. These deposits have the potential to preserve animals even though definitive animal fossils have eluded discovery within them, and they have previously served as maximum dates for animal origins in other studies. When the molecular clock was anchored to these older formations rather than to the Ediacaran Weng’an deposit, the estimated origin of animals shifted backwards by around 200 million years, landing between 800 and 700 million years ago.

That timeline is not without independent support. Chemical fossils, known as biomarkers, preserved in ancient rocks provide evidence consistent with sponges living at least 650 million years ago, tens of millions of years before the oldest definitive macroscopic animal fossils appear. The molecular clock estimate also raises a provocative possibility: animals may already have evolved before Earth entered the Cryogenian glaciations, or even emerged during that inhospitable interval. The Cryogenian Period began around 720 million years ago, when enormous glaciers spread across the planet in episodes commonly known as Snowball Earth. The new study reopens the question of whether the dramatic environmental conditions associated with those global ice ages played a role in the origin and early evolution of animal life, a possibility that had been closed off under the younger Ediacaran timeline.

First author Orin Lole Durbin, who conducted the work as an undergraduate at Oxford and is now at Virginia Tech, cautioned that the analysis does not prove animals existed 800 million years ago. Pre-Ediacaran animal body fossils still elude researchers, and the molecular clock provides an estimate rather than a direct observation. However, the new fossil evidence from Mongolia undermines one of the main arguments for restricting animal origins to the Ediacaran interval, while the molecular-clock analyses show how much further back their evolutionary history could extend. The distinction matters: the study does not claim to have found ancient animals, but it removes a key obstacle to the idea that they existed far earlier than the rocks currently reveal.

Part of the reason early animals remain so elusive lies in their biology. The first animals would have been small and soft-bodied, lacking the shells, bones and other hard structures that make later animals so much easier to fossilise. Whether such creatures were preserved at all depended on their environment and on an unusual combination of chemical conditions after death, conditions that evidently failed in the Kheseen setting even as exquisite microfossils of other organisms formed. The researchers argue that future work should therefore explore fossil deposits from different parts of the world, representing different environments and modes of fossilisation, in the search for animals. Such searches should also weigh all available lines of evidence, including body fossils, traces of animal activity and chemical biomarkers, rather than relying on any single signal. Until that evidence becomes available, as Anderson noted, the precise birth date of the animal kingdom remains uncertain, but the window of possibility has now swung dramatically open toward the deep Neoproterozoic.

Subject of Research: Re-evaluating fossil calibration constraints on the molecular clock timing of animal origins

Article Title: New study suggests animals may have evolved vastly earlier than fossil evidence suggests

Article References: New study suggests animals may have evolved vastly earlier than fossil evidence suggests. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: animal origins, molecular clock, Ediacaran, Neoproterozoic, Weng'an Biota, Kheseen Biota, Snowball Earth, Cryogenian, microfossils, sponges, Cambrian explosion, fossil record

The research, led by scientists at Nanjing University in collaboration with David Fike, the Glassberg/Greensfelder Distinguished University Professor of Earth, Environmental, and Planetary Sciences at Washington University in St. Louis, was published in the Proceedings of the National Academy of Sciences. The team examined tubular fossils of soft-bodied Ediacaran animals and found geochemical signatures consistent with the same kind of sulfide-based microbial partnership that sustains modern tube worms. The finding pushes credible evidence for chemosymbiosis back to the dawn of multicellular life, addressing a question that has lingered in evolutionary biology for decades: did these partnerships arise recently, as animals diversified into complex ecosystems, or were they present from the very beginning?

Chemosymbiosis is difficult to study in the deep past because it leaves almost no conventional fossil evidence. Symbiotic bacteria live inside soft tissues, and soft tissues rarely survive the rigors of burial, compression, and geological time. The fossil record of animal-microbe symbiosis is therefore, as Fike describes it, sketchy. Most of what paleontologists know about ancient symbiosis comes from rare windows of exceptional preservation, where delicate anatomies are captured in fine-grained sediments. But even in those cases, distinguishing true internal symbiosis from surface contamination or opportunistic colonization is notoriously difficult. The new study sidesteps this limitation by targeting not the animal tissue itself but the mineral that replaced it during fossilization.

Pyrite, iron sulfide, is the key. When organic remains decay in oxygen-poor seafloor sediments, sulfate-reducing bacteria generate hydrogen sulfide, which reacts with iron in the surrounding sediment to precipitate pyrite. In many Ediacaran fossils, this process preserved three-dimensional casts of tubular organisms entirely in pyrite. Crucially, the isotopic composition of the sulfur inside that pyrite records the chemistry of the microenvironment in which the animal lived and decayed. If an animal hosted sulfur-metabolizing bacteria, the local sulfur cycle around its body would have been dramatically altered compared with the open seawater. Those alterations, encoded in sulfur isotope ratios, can survive hundreds of millions of years in the rock record.

The Ediacaran Period, spanning roughly 635 to 540 million years ago, was a strange and pivotal chapter in Earth history. It followed the severe glaciations of the Cryogenian and preceded the Cambrian explosion, the rapid diversification event that produced most major animal body plans. Ediacaran oceans were chemically hostile by modern standards: oxygen was scarce in deeper waters, while hydrogen sulfide accumulated in sediments and much of the water column. The first multicellular animals evolved in this challenging setting, and one long-standing hypothesis holds that microbial partnerships may have helped make these toxic oceans more hospitable, effectively extending the habitable space available to early animal life.

The animals at the center of the new study were tubular organisms, often described as proto-worms, that lived on or in the seafloor. By analyzing the sulfur isotope composition of pyrite within and around these fossil tubes, the researchers detected patterns that are difficult to explain by normal seawater chemistry alone. Instead, the data point to intense, localized sulfur cycling consistent with the activity of sulfide-oxidizing microbes associated with the animal, mirroring the geochemical footprint produced by chemosymbiotic relationships in modern marine ecosystems. In effect, the fossils preserve a chemical echo of the same metabolic bargain struck today between tube worms and their bacterial tenants.

Fike emphasized the broader evolutionary significance of the result. Rather than being a relatively recent innovation that emerged as animals diversified into complex Cambrian ecosystems, chemosymbiosis appears to have been a very early evolutionary strategy, one that helped animals survive and spread throughout the ocean. That timing matters because it reframes the role of microbes in the origin of animal life. If the first multicellular organisms were already relying on bacterial partners to detoxify their surroundings and supplement their nutrition, then symbiosis was not an accessory to animal evolution but potentially one of its enabling conditions.

The technical achievement underlying the study lies in the precision of modern isotope geochemistry. High-resolution secondary ion mass spectrometry and related analytical techniques allow researchers to measure isotope ratios at micrometer scales within individual fossils, resolving spatial variations that bulk analyses would average away. Applied to pyritized Ediacaran tubes, these methods can distinguish sulfur derived from open seawater from sulfur processed through microbial metabolisms. Multiple sulfur isotopes provide particularly strong constraints, because different microbial pathways, including sulfate reduction and sulfide oxidation, leave characteristically different isotopic signatures. The convergence of these signals within the fossils forms the core of the evidence for ancient chemosymbiosis.

The implications extend beyond the Ediacaran. Chemosymbiosis remains a cornerstone of modern deep-sea ecosystems, sustaining hydrothermal vent communities, cold seep faunas, and other chemosynthetic habitats that flourish independently of sunlight. If this strategy was already established more than half a billion years ago, it suggests remarkable evolutionary continuity: the metabolic machinery that powers vent ecosystems today may have been assembled in the Proterozoic oceans where animal life first took hold. It also raises new questions about how many other Ediacaran organisms harbored microbial partners, and whether symbiosis helped early animals tolerate the low-oxygen, high-sulfide conditions that characterized their world.

For now, the study stands as a vivid demonstration of what geochemistry can recover from fossils that preserve no anatomy at all. A tubular animal that left behind no bones, shells, or soft tissues still recorded its way of life in the isotopic architecture of the pyrite that entombed it. The old friends that sustain tube worms on the modern seafloor, it turns out, were old already when the first animals appeared, quietly reshaping a toxic ocean into a place where complex life could take root and eventually flourish.

Subject of Research: Geochemical evidence for chemosymbiosis in Ediacaran tubular animals

Article Title: Get by with a little help from (old) friends

Article References: Get by with a little help from (old) friends. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: chemosymbiosis, Ediacaran, pyrite fossils, sulfur isotopes, tube worms, Cambrian explosion, symbiosis, geochemistry, early animal evolution, sulfide oxidation, paleontology, Nanjing University