Overview of variability in Fineness Ratio and regional vertebral count data within the analyzed data sets. A, Range of Fineness Ratio (FR) values calculated for species sampled within the chondrostean, esociform, beloniform, and lepisosteiform data sets, including outgroup taxa. Species with the smallest and largest values for FR are illustrated for each clade: Birgeria groenlandica and Saurichthys striolatus (chondostreans); Callipurbeckia minor and Lepisosteus osseus (Lepisosteiformes); Palaeoesox weileri and Esox tiemani (Esociformes); Oryzias profundicola and Pseudotylosurus (Beloniformes). FR measures the relationship between body length and depth (right, inset). B, Bar graph illustrating the range in abdominal and caudal vertebral counts for species sampled within each dataset, including outgroup taxa. Note the greater range of abdominal counts than caudal counts in the lepisosteiform, beloniform and esociform data sets. The large range of caudal counts seen in the ‘Sphyraenidae’ data set stems from the inclusion of Pleuronectiformes as an outgroup.