How are hinge and tooth types used to classify articulate lamp shells?

Articulate lamp shells (brachiopods) are classified based on the presence of teeth and sockets that allow their valves to articulate. Within this group, the specific morphology of the hinge teeth is a key diagnostic feature used to distinguish between different types.12

Teeth are categorized into two primary types:

• Deltidiodont teeth: These teeth grow anteriorly along with the palintrope (a shelf between the beak and the hinge line). As they develop, they leave a distinct growth path along the edge of the delthyrium, which is the triangular opening for the pedicle.12
• Cyrtomatodont teeth: These are knoblike structures found in shells that lack a hinge line. While they also grow anteriorly, they are maintained in their knoblike shape through a process of posterior resorption.1

These tooth types, along with other structural characteristics such as the presence of dental plates or a spondylium (united dental plates), help paleontologists identify and classify various genera and orders of articulate brachiopods.12