ALT Cumulative disparity (Procrustes variance) of trilobite cephalic structures across Cambrian Series 2 (c. 521–509 Ma). Cumulative disparity on left vertical axis; cumulative diversity (families) on the right; horizontal axis indicates time. Analysed configurations are shown with landmarks (red) and sliding semi-landmarks (grey). Black squares indicate observed disparity; light blue circles indicate randomized disparity with 95% confidence intervals. Taxonomic diversity (number of families) is also shown (black line). Disparity quickly achieves a maximum and generally decreases thereafter, suggesting rapid filling to the extremes of morphospace.