Developmental and functional controls on enrolment in an ancient, extinct arthropod

Area of Science:

• Paleontology
• Developmental Biology
• Arthropod Evolution

Background:

• The trilobite *Aulacopleura koninckii* is a key model organism for studying ancient arthropod development.
• Understanding exoskeletal enrolment mechanics is crucial for reconstructing ancient arthropod behavior and development.

Purpose of the Study:

• To investigate changes in exoskeletal enrolment mechanics during the development of *Aulacopleura koninckii*.
• To correlate developmental changes with variations in segment number and environmental factors.

Main Methods:

• Utilized three-dimensional models to analyze exoskeletal enrolment.
• Examined changes in segment number, size, and allocation during growth.

Main Results:

• Identified a shift in enrolment style from sphaeroidal in early growth to non-sphaeroidal in later growth.
• Observed that later-stage enrolment involved the posterior trunk extending beyond the head.
• Linked this enrolment change to the species' known variation in mature segment number.

Conclusions:

• The transition in enrolment style facilitated adaptation to varying trunk segment numbers during development.
• This developmental plasticity may have been influenced by challenging environmental conditions, such as low oxygen levels.
• The study provides insights into how precisely controlled early development allows for later life adaptations in trilobites.