A small part of the anterior end of the basisphenoid and two short fragments of a narrow parasphenoid are visible through the posterior interpterygoid vacuity; their morphology remains unclear (Figure 3B).
The internal nares are located halfway between the anterior end of the snout and the anterior margin of the posterior interpterygoid vacuity.
They enclose an anterior interpterygoid vacuity, as in M.
The right one is located ventrally over the posterior interpterygoid vacuity and the left one is moved to the right edge of the cranium (Figure 3B).
The Barremian pliosaurid genera known in Colombia, Stenorhynchosaurus and Acostasaurus, are smaller in size and clearly differ from the new specimen MP111209-1: Stenorhynchosaurus has a more elongated snout, isodont dentition, and longer mandibular symphysis (Paramo-Fonseca et al., 2016); and Acostasaurus has a shorter preorbital rostrum, large nasal present in contact with the parietal, anterior interpterygoid vacuity absent, longer mandibular symphysis, different arrangement of the heterodont dentition (Gomez-Perez and Noe, 2017), cervical rib facets in ventrolateral position and double-headed cervical ribs (Gomez-Perez, 2001).
Both of the diagnoses include significant characters than cannot be observed in "K." boyacensis": in the definition of Kronosaurus, Kear (2003) includes premaxilla with four large caniniform teeth, anterior interpterygoid vacuity absent, ectopterygoid and pterygoid forming lateral flanges united in a short dished contact ventrolateral to the posterior interpterygoid vacuity, and mandibular symphysis extended back to sixth tooth position; and in the definition of K.