Fig. 5
From: Developmental transformations in Jurassic driftwood crinoids
Crowns grew by accretionary enlargement of ossicles and by the introduction of new ones at the arm tips (axillaria drawn in black). The switch from iso-to-heterotomous branching was not sudden: Arm sections following the last isotomies are longer in the outer versus the inner branches. The finer pinnulae (not drawn) filled spaces between the parallel ramuli. As indicated by numbers, new ramuli were constantly introduced in proportion to the length of the stem