Gregarious behaviour in Carboniferous cyclidan crustaceans.

Area of Science:

• Paleontology
• Marine Biology
• Evolutionary Biology

Background:

• Gregarious behaviors in arthropods are linked to defense, mass molting, and reproduction.
• Crustacean fossil records of gregariousness are rare, hindering understanding of its evolutionary history.
• Extinct pancrustaceans, Cyclida, offer a potential avenue for studying gregarious behavior due to limited prior research.

Purpose of the Study:

• To investigate gregarious behavior in the extinct crustacean order Cyclida.
• To identify and analyze aggregations of fossil crustaceans to understand their ecological significance.
• To expand the fossil record of crustacean gregariousness and its evolutionary origins.

Main Methods:

• Excavation and analysis of fossil specimens from the Bear Gulch Limestone, Montana, USA.
• Detailed examination of articulated specimens, including appendages and potential gill preservation.
• Paleoecological interpretation of fossil clusters to infer behavior and environmental conditions.

Main Results:

• Discovery of a significant cluster comprising 50 individuals of *Schramine montanaensis*.
• The cluster's preservation suggests rapid burial, preserving articulated specimens.
• This finding represents one of the oldest documented instances of crustacean gregariousness.

Conclusions:

• The *Schramine montanaensis* cluster likely represents either a mass molting event or individuals clustering for shelter.
• This discovery offers crucial insights into the life modes and ecological interactions of Cyclida during the Carboniferous period.
• The findings contribute significantly to understanding the early evolution of gregariousness in crustaceans.