Table 4. Optimized synontomorphies supporting the growth stages of Tylosaurus kansasensis/nepaeolicus.

Growth Stage	Unambiguous	Ambiguous
1	n/a	n/a
2	None	Quadrate tympanic ala thick**, quadrate alar concavity shallow**
3	Premaxilla-maxilla suture u-shaped	None
4	Premaxillary rostrum foramina small**, quadrate mandibular condyle rounded	Frontal-parietal suture flanges small**, jugal ascending ramus thick, pterygoid ectopterygoid process thick, basioccipital ossified
5	QH ≥13% TSL, quadrate ala rim defined, dorsal ridge of dentary predental process present	Quadrate suprastapedial process intermediate length**, parietal posterior pegs absent*
6	QH between 50 and 99 mm, quadrate mandibular condyle ossified	TSL between 400 and 800 mm, quadrate infrastapedial process present**, frontal-parietal suture flanges large*
7	Premaxillary rostrum foramina large**	Dentary deep
8	Jugal posteroventral angle obtuse**, coronoid posteroventral process present as bump*	None
9	None	Parietal lateral borders straight**
10	Quadrate suprastapedial process thick, coronoid anterolateral notch present and shallow	None
11	Premaxillary rostrum distinctly knobbed, frontal posterolateral processes thick, increase in dentary teeth* (13 to 14)	Frontal dorsal crest absent**
12	QH between 150 and 199 mm	TSL between 800 and 999 mm, premaxillary rostrum ≥5% TSL, premaxilla-maxilla suture rectangular

Note:

Reversals are bold, phylogenetic characters are indicated by an asterisk, and characters that are purportedly diagnostic of T. kansasensis or T. nepaeolicus are indicated by two asterisks.