Saakshi Bangera, DY Patil School of Biotechnology and Bioinformatics
Microbial structures present on the bottom of the water body (stromatolites) provide obvious evidence of pre-Phanerozoic life. Since these structures are difficult to understand, scientists have struggled to decode their microscopic laminae and clots. The presence of trace fossils and a bilaterian body indicates the existence of metazoans by the last period of the Neoproterozoic era. Since the geochemical evidence disputes this indication, there is an ongoing search for definitive proof.
The search for evidence is backed by uncertainty about what to look for. Physical evidence of the existence of sponges could be helpful because sponges are the most basic of known animals. Evidence of the early metazoan period shows the existence of preservational products of soft-tissue sponges instead of mineralized ones. The molecular clock data suggest that sponges came into existence in the early Neoproterozoic era. It also suggests the Cambrian period witnessed the oldest undisputed sponge body.
An unusual microscopic feature of Phanerozoic reefs and was interpreted as proof of relation with protozoans or algae. This interpretation was incorrect. The vermiform structure was, on the other hand, a keratose sponge body fossil comprising cement-filled microtubules bound in carbonate microspar. Despite interrogating the credibility of this analysis, the body fossils of Phanerozoic sponges undisputedly confirm the association between vermiform microstructures and sponges.
Thin sections of sponge body fossils from around 890-million-year-old Little Dal reefs offer possible evidence of this study. Researchers found the reefs to grow in five different stages, each with a characteristic morphological feature.
Results and discussion
The vermiform structures of the samples were rarely identifiable in thin sections. In these sections, it forms millimetre-to-centimetre-scale masses of tubes filled with calcite mast and calcite microspar groundmass in the surrounding area. The shape and polygonal meshworks of the vermiform tubules of Little Dal resemble two organisms namely –
- Spongin fibre networks of modern keratose sponges
- The microstructure is interpreted to be derived from the sponge in Phanerozoic microbial rocks.
The compositional homogeneity and the texture of the microspar groundmass are indicative of an origin through permineralization of previously existing biological substances. This is in contrast to the incremental accumulation of sediments. Detailed comparison of the characteristics of vermiform structures concedes no alternative to the sponge interpretation. The study shows that Little Dal vermiform microstructure prefers environments without photosynthetic calcimicrobes such as reef flanks, and shelter voids. The study also demonstrates that these microstructures do not prefer filamentous calcimicrobial reef-framework components. This preference suggests that
- Illumination is probably not a requirement for the microstructure formation
- The organism may have been incapable of competing with reef-building photosynthesizers
The interlayer of vermiform structure supports the understanding that such organisms are incapable of competing with reef-building cyanobacteria. Instead, vermiform-microstructured organisms occupy niches that filamentous calcimicrobes do not inhabit. These organisms occupy places with poor illumination or high hydrodynamic energy.
If the vermiform-microstructures in the Little Dal reefs are acknowledged as early fossils of the sponge body, the following implications will be made
- From the Neoproterozoic oxygenation event, the emergence of metazoans was decoupled
- Neoproterozoic glacial episodes did not affect the early animal life
- Little Dal objects are older than approximately 350 million years
Conclusion
The study provides the material that represents the oldest body-fossil of animals known to date. It also provides the first physical evidence that animals survived through the Cryogenian glacial episodes. There is a strong indication that animals emerged before the Neoproterozoic oxygenation event.
Also read: GATE 2022: Examination dates and new subjects added!
Reference
Turner, E.C. Possible poriferan body fossils in early Neoproterozoic microbial reefs. Nature (2021). https://doi.org/10.1038/s41586-021-03773-z
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About the author
The author is currently pursuing MSc in Biotechnology from DY Patil School of Biotechnology and Bioinformatics. She believes that she doesn’t have a specific area of interest yet. She wishes to explore toxicology and food biotechnology. She’s quite passionate about Biotechnology and aims to grab every opportunity she comes across.
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