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Pellet microfossils: Possible evidence for metazoan life in Early Proterozoic time

E I Robbins1, K G Porter, K A Haberyan

  • 1U.S. Geological Survey, National Center MS 956, Reston, VA 22092.

Proceedings of the National Academy of Sciences of the United States of America
|September 1, 1985
PubMed

Insights

Microfossils resembling fecal pellets provide evidence of early animal life. These ancient pellets suggest a complex food chain existed 1.9 billion years ago, predating other complex life forms.

Area of Science:

  • Paleontology
  • Geology
  • Biogeochemistry

Background:

  • Microfossils are key to understanding early life.
  • Fecal pellets are indicative of animal activity and food chain complexity.
  • Sedimentary rocks preserve evidence of ancient environments and life.

Purpose of the Study:

  • To investigate the occurrence and significance of microfossils resembling fecal pellets in ancient sedimentary rocks.
  • To determine the age and environmental context of these microfossil occurrences.
  • To assess the implications for the early evolution of animal life and food webs.

Main Methods:

  • Analysis of acid-resistant residues from shale samples.
  • Examination of thin sections of sedimentary rocks.
  • Geological dating and facies analysis of rock formations.

Main Results:

  • Microfossils resembling fecal pellets (50 x 110 µm) were found in Middle Cambrian to Early Proterozoic shale (0.53–1.9 Gyr).
  • These pellets were found in dark gray/black rocks deposited in environments analogous to modern pellet preservation sites.
  • Archean rocks (2.68–3.8 Gyr) of similar lithology were barren of these microfossils.

Conclusions:

  • The Proterozoic microfossils, if interpreted as fecal pellets, indicate metazoan life and complex food chains at 1.9 Gyr ago.
  • This finding potentially predates macroscopic metazoan body fossils (0.67 Gyr) and animal trace fossils (0.9–1.3 Gyr).
  • The absence in Archean rocks suggests a significant evolutionary threshold was crossed in the Proterozoic Eon.

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