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A study in Current Biology traces collagen-digesting enzymes across 700 bacterial genomes and finds that collagenases spread into oxygen-using bacteria around the Ediacaran-Cambrian transition. The researchers propose that faster microbial decay may help explain why soft-bodied fossils became less common, but the study presents an explanation, not proof that this was the sole cause.
A Cambridge-led study proposes that the spread of collagen-digesting enzymes among oxygen-using bacteria around the Ediacaran-Cambrian transition may help explain why soft-bodied animal fossils became less common. The research, published in Current Biology, links the microbial change to the decline in preservation, but does not establish it as the only cause of gaps in the fossil record.
Collagen is a structural protein in animal tissues. After an animal dies, microbes with collagenases can break down collagen, potentially shortening the time available for the remains to be buried and fossilised. The study’s authors say that before collagen-degrading enzymes were widespread in oxygen-using microbes, collagen in dead animals could persist longer in some settings.
Lead author Philip Vixseboxse, who completed the work as a PhD candidate in Cambridge’s Department of Earth Sciences, and co-authors traced collagenase genes across 700 bacterial genomes and compared their distribution with a time-dated tree of life. They report that collagenases are older than animals and were initially found in anaerobic microbes, which cannot tolerate oxygen. Later, the genes spread into a wider range of microbial groups, including aerobic bacteria associated with modern decay.
The researchers place that spread around the transition from the late Ediacaran Period, 579 million to 539 million years ago, into the Cambrian. They argue that the timing corresponds with a marked decline in soft-bodied fossils. The paper’s interpretation is that collagen-degrading microbes may have made decay faster, so remains needed to be buried more quickly to survive long enough to fossilise.
How Microbes Could Change Fossil Preservation
The proposed mechanism offers a biological explanation for a longstanding puzzle: some late Ediacaran animals had no hard parts, yet their fossils can preserve detailed body forms and entire communities. Fossilisation is not a direct census of past life; it records which remains survived decay and geological processes. If microbes altered the rate at which soft tissue broke down, changes in the fossil record could partly reflect changing preservation conditions rather than only changes in animal abundance.
The study also connects microbial evolution to the quality of evidence available to reconstruct early animal life. If soft tissues became harder to preserve as collagenases spread, researchers may have fewer fossils from later periods even where soft-bodied organisms were present. That possibility can inform how scientists interpret apparent disappearances or shifts in ancient ecosystems, though it does not by itself identify which organisms were missing.
The authors draw a limited analogy with modern plastic: both collagen and some polymers can persist until organisms evolve or acquire ways to break them down. Vixseboxse said microbes may someday exploit enzymes that degrade plastic, but described that as a possibility far in the future. The study does not show that plastic-degrading enzymes will evolve or predict when they might.
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Why Ediacaran Fossils Stand Out
The fossil record is incomplete because hard parts such as shells, bones and teeth generally have better chances of preservation than skin, muscles and organs. Most fossils known today are mineralised remains, while soft tissues usually decay before fossilisation can occur.
Late Ediacaran sites are an exception. They preserve some of the oldest known complex animal life, despite the animals’ lack of hard body parts. Researchers have proposed several explanations for these exceptional fossils, including distinctive ocean chemistry, differences in tissue composition and a microbial layer on the seafloor. The Cambridge team says those explanations may apply in some locations but do not account for every case. Its enzyme hypothesis is intended as a broader biological mechanism that could operate across different settings.
Soft tissues can still be preserved in younger rocks under exceptional circumstances. For example, rapid burial by sediment may protect a body from decay. The study therefore does not suggest that collagenases made later soft-bodied fossilisation impossible; rather, the researchers argue that faster decay may have made preservation less likely unless burial occurred quickly.
“Around this critical time when these soft-bodied animals stopped fossilising, we start seeing the appearance of collagenases in aerobic bacteria.”
— Philip Vixseboxse, lead author
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Limits of the Enzyme Evidence
The findings support a proposed link, not proof that collagenases alone caused the decline in soft-bodied fossils. The study compares the history of enzyme genes with fossil-record timing; the source report does not establish that microbial enzyme spread was the sole driver or quantify how much it affected preservation. Other factors, including the conditions at a burial site, remain relevant.
It is also unclear how consistently the proposed process operated across different marine environments. The authors note that earlier explanations may work in some locations, and younger soft-bodied fossils are known where circumstances favoured rapid preservation. The available account does not identify a single mechanism that explains every Ediacaran fossil site or every gap in the record.
The research traces collagenase genes through bacterial genomes, but the report does not provide a detailed breakdown of how many genomes belonged to each group or how directly gene histories map onto the activity of ancient microbial communities. Those limits mean the timing and ecological effect should be understood as the researchers’ interpretation of multiple lines of evidence.
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Testing the Preservation Hypothesis
The study does not announce a specific follow-up experiment or a scheduled next milestone. Further tests would need to compare the proposed enzyme history with evidence from fossil sites and assess whether the timing holds across different environments. Researchers could also examine how burial conditions and local microbial communities affected the preservation of soft tissues.
For now, the central development is the authors’ proposed explanation, published in Current Biology: as collagenases spread into aerobic bacteria, decay may have become more effective in settings where oxygen was available. Whether this mechanism can account for a substantial share of the fossil-record change, alongside other environmental and geological factors, remains open.
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Key Questions
What did the study find?
The researchers traced collagenase genes across 700 bacterial genomes and report that these enzymes spread into a wider range of microbes, including oxygen-using bacteria, around the Ediacaran-Cambrian transition. They propose that this helped speed the decay of collagen-rich animal tissues.
What are collagenases?
Collagenases are enzymes that break down collagen, a structural protein found in animal tissues. The study focuses on microbes that carry genes for producing these enzymes.
Does the research prove why soft-bodied fossils became rarer?
No. It presents a proposed link between the spread of collagenases and declining soft-tissue preservation. The findings do not establish that enzyme spread was the only cause of the change.
Why were some Ediacaran animals preserved without hard parts?
The late Ediacaran fossil record includes detailed remains of animals that lacked shells or bones. Scientists have considered several explanations, including ocean chemistry and seafloor microbial layers. The new study adds microbial collagen breakdown as a possible broad factor.
Can soft-bodied animals still fossilise today?
Soft tissues can be preserved in younger rocks in exceptional conditions, such as rapid burial that limits decay. The study’s hypothesis concerns reduced preservation chances, not an absolute end to soft-tissue fossilisation.
Source: hn
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