The extraxial axial theory is used to investigate homology of ambulacral and oral plating because it predicts terminal branching and terminal addition of plates in the axial skeleton, although excepti
# **SHCMS:G.07547** **Crinoid holdfast.** Model of a silurian crinoid holdfast; the root-like structure that attached these animals to the sea floor. Found on wenlock Edge. Age: approx 425 million
