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The two phases of the Cambrian Explosion
Andrey Yu Zhuravlev1, Rachel A Wood2
1Department of Biological Evolution, Faculty of Biology, Moscow State University named after M.V. Lomonosov, Moscow GSP-1, 119991, Russia.
Scientific Reports
|November 11, 2018
Summary
The Cambrian Explosion involved two phases: stem group diversification in the Ediacaran and early Cambrian, followed by crown group radiation after the Sinsk extinction event. This reveals distinct evolutionary dynamics of early animal life.
Area of Science:
- Paleontology and Evolutionary Biology
- Study of early metazoan diversification and the Cambrian Explosion
Background:
- The Cambrian Explosion, a period of rapid metazoan diversification, remains incompletely understood.
- Understanding the evolutionary dynamics of lophotrochozoan skeletal species is key to deciphering this event.
Purpose of the Study:
- To quantitatively analyze the temporal distribution of lophotrochozoan skeletal species from the Ediacaran to Cambrian Stage 5.
- To distinguish between stem and crown groups using morphological traits and determine their diversification patterns.
Main Methods:
- Quantitative analysis of fossil occurrence data for 430 lophotrochozoan skeletal species from the Siberian Platform.
- Utilized morphological traits to differentiate between stem and crown group taxa.
- Examined temporal distribution across geological time intervals, including the Ediacaran, Cambrian Stages, and the Sinsk extinction event.
Main Results:
- Skeletal stem group lophophorates, brachiopods, and molluscs appeared in the terminal Ediacaran (~542 Ma) and diversified, but were decimated by the Sinsk extinction event (~513 Ma).
- Crown group brachiopod and mollusc species emerged later (~537 Ma), radiated in Cambrian Stage 3, and persisted through the Sinsk Event with minimal diversity loss.
- The diversification of these groups occurred across the Ediacaran/Cambrian boundary and the Basal Cambrian Carbon Isotope Excursion (BACE) interval.
Conclusions:
- Propose two distinct phases of the Cambrian Explosion separated by the Sinsk extinction event.
- Phase 1 (Ediacaran to early Cambrian Stage 4) was dominated by stem group diversification.
- Phase 2 (post-Sinsk Event) was characterized by the radiation of bilaterian crown group species, extending into the Ordovician.
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