Grouping behavior in a Triassic marine apex predator.

Area of Science:

• Paleontology
• Marine Biology
• Evolutionary Biology

Background:

• Marine tetrapods play key ecological roles and often form aggregations.
• Grouping behaviors in marine tetrapods are driven by prey, social factors, or oceanography.

Purpose of the Study:

• To investigate early marine tetrapod grouping behaviors.
• To document evidence of aggregation in the giant ichthyosaur Shonisaurus.

Main Methods:

• Analysis of numerous Shonisaurus specimens from the Luning Formation, Nevada.
• Examination of fossil distribution, abundance, and demographic composition.
• Integration of geological evidence from the Late Triassic marine environment.

Main Results:

• A large, monotaxic assemblage of Shonisaurus fossils spanning extensive area and time.
• Disproportionate abundance of large individuals and neonatal/embryonic specimens, lacking intermediate juveniles.
• Evidence suggests Shonisaurus formed dense aggregations in a tropical marine environment for millennia.

Conclusions:

• Philopatric grouping behavior in marine tetrapods is at least 230 million years old.
• Shonisaurus aggregations were potentially linked to reproductive activities.
• This study reveals ancient social behaviors in early marine vertebrates.