Phylomorphospace occupation in chondrosteans. A, Relationship between the number of abdominal vertebrae and fineness ratio. B, abdominal and caudal vertebral numbers. Nodes along the backbone of the tree are indicated in black unless they are within one of the indicated higher taxonomic units; the root is indicated by a bullseye. Terminal taxa are represented by nodes connected only to a single branch; hypothetical ancestral states are represented by nodes connected to at least three branches. The placement of the hypothetical ancestral nodes was calculated using weighted squared change parsimony.