Figure 5. Ontogram of one Tylosaurus sp. specimen and 22 Tylosaurus proriger specimens based on a quantitative cladistic analysis.

The ontogram is a single tree and tree statistics are summarized in the upper left. Character states that define each growth stage are shown along the main branch, and the exemplar specimens are to the left of the main branch; the most mature individual, identified by the analysis with an artificial adult, is indicated by an arrow. The encircled numbers on the nodes are the growth stages, and the numbers to the right of them are the bootstrap and jackknife values, respectively (1,000 replicates, <50% not shown). Unambiguous character reversals are shown in red. “Immature” specimens were recovered in the lower third of the tree, “intermediate” specimens were recovered in the middle third of the tree, and “mature” specimens were recovered in the upper third of the tree. The ontogram supports the assignment of all specimens to T. proriger and does not show evidence of sexual dimorphism. Specimen photographs are not to scale; FHSM VP-14845 is a neonate only referable to Tylosaurus sp.; KUVP 5033 is included in the analysis with all three Tylosaurus taxa, but not in the individual T. proriger ontogram; the photographs of the skull of KUVP 1032 and the quadrate of FMNH UR902 have been inverted to face left.