Quadrate orientation and joint reaction force underwent correlated evolution during suchian evolution.

Area of Science:

• Paleontology
• Biomechanics
• Vertebrate Anatomy

Background:

• The quadrate bone is a crucial skeletal element in the jaw joint of nonmammalian vertebrates.
• It plays a vital role in resisting joint reaction forces (JRF) during feeding.
• Previous research suggested quadrate orientation reflects muscle anatomy and JRF.

Purpose of the Study:

• To quantitatively test the hypothesis that quadrate orientation correlates with JRF orientation.
• To investigate the evolution of the quadrate and its role in the feeding system of suchians, the lineage leading to crocodiles.

Main Methods:

• Utilized detailed, three-dimensional biomechanical modeling to estimate JRF.
• Analyzed a sample of eleven fossil and extant suchians.
• Quantified the similarity between quadrate orientation and JRF orientation using the cross-product of orientation vectors.

Main Results:

• Demonstrated a tight coupling between the angle of the quadrate in the sagittal plane and JRF orientation.
• Confirmed the longstanding hypothesis regarding the correlation between quadrate orientation and JRF.

Conclusions:

• The study reveals coordinated evolution between JRF and quadrate anatomy during suchian evolution.
• Provides a framework for analyzing evolutionary changes in joint anatomy and biomechanics in extinct and extant vertebrates.