Dynamic and synchronous changes in metazoan body size during the Cambrian Explosion

Area of Science:

• Paleontology
• Evolutionary Biology
• Geochronology

Background:

• The drivers and evolutionary dynamics of the Cambrian Explosion remain incompletely understood.
• Quantifying high-resolution changes in species body size provides insights into metazoan evolutionary responses.

Purpose of the Study:

• To analyze high-resolution body size changes in major metazoan groups during the Early Cambrian on the Siberian Platform.
• To correlate body size trends with origination rates, species diversity, and environmental events.

Main Methods:

• High-resolution body size quantification of fossil species.
• Analysis of temporal trends in body size, origination, and diversity.
• Correlation of evolutionary dynamics with known geological events like the Sinsk anoxic extinction.

Main Results:

• Archaeocyath sponges, hyoliths, and helcionelloids exhibited synchronous body size fluctuations, peaking in the late Early Cambrian and decreasing after the Sinsk anoxic event.
• These synchronous trends positively correlated with origination rates and species diversity.
• Calcitic brachiopods showed increasing body size with diversity, while phosphatic brachiopods showed a decrease; both groups recovered rapidly post-Sinsk Event.

Conclusions:

• Synchronous body size changes in some groups suggest external drivers like oxygenation or productivity shifts.
• Differential responses in brachiopods indicate varied physiological adaptations.
• These dynamics shaped the evolutionary trajectory and termination of the Cambrian Explosion.