Emydid Shell Kinesis: Biomechanics and Evolution

Abstract

Mechanisms of shell closure in box turtles of the family Emydidae have been analyzed with respect to functional anatomy, evolution and phylogenetic significance. Structural requirements essential to the box turtle morphotype are: 1) plastral kinesis; 2) mechanisms for displacement (accommodation) of the limb girdles as the shell is closed; 3) additional space in the shell for displacement of the forelimbs; 4) musculature to effect shell closure. Girdle accommodation is structurally and evolutionarily the most difficult requirement; plastral kinesis is the least.