LAUSR

Abstract The reassessment of a lower jaw fragment of a mosasaur from the upper Maastrichtian of central Chile (Q.3105) indicates that the specimen does not belong to Plotosaurus, as previously suggested by Frey et al. in 2016. The specimen does not show the characteristics of Plotosaurus, such as the long projection anterior to the anteriormost tooth socket of the dentary, the ventrally positioned Meckelian canal, nor does it possess teeth with enamel coarsely striated at the base of the crown and a smooth apex. We continue in agreement to the previous assignment to Halisaurinae indet. proposed by Jimenez-Huidobro et al. in 2015. Even more, tooth morphologies such as the curvature pattern and the smooth and finely striated enamel, plus dentary characters such as the curvature of that bone, and the medially located Meckelian canal, support the assignment of the specimen Q.3105 to Halisaurus sp. Affinities of Q.3105 with the halisaurine genus Eonatator are discarded, due to the shape in cross section and size of marginal teeth that decreases distally in the latter, traits not seen in the specimen Q.3105. This specimen represents the fourth halisaurine described from South America, and the second Maastrichtian halisaurine from the southernmost part of the continent. This record contributes to the understanding of the broad distribution that halisaurines reached during the Late Cretaceous.