Cranial anatomy of a Maastrichtian (Upper Cretaceous) mosasaur (Squamata, Mosasauridae) from north-east Mexico

Aug 27, 2026

First mosasaur known from Mexico with significant cranial remains is reported from the late Early Maastrichtian Méndez Formation of Nuevo León in north-east Mexico. The specimen includes a fragmentary skull and mandibular parts, with anatomical traits indicating a juvenile individual. The skull shows a rostral tuberosity on the premaxilla and a distinctive combination of cranial characters, yet its affinities to other mosasaurs remain unclear due to incomplete material and limited understanding of the biological significance of classification characters in Mosasauridae.

LanguageEnglish

CategoryResearch & Report

FormatPDF

Pages15

Reading Time38 min

AccessFree to download

Abstract

Introduction

Background on mosasaurs and classification

Regional context: Mexico and prior finds

Material from the Méndez Formation

Revista Mexicana de Ciencias Geológicas, v. 24, núm. 1, 2007, p. 89-103 89 Cranial anatomy of a Maastrichtian (Upper Cretaceous) mosasaur (Squamata, Mosasauridae) from north-east Mexico Marie-Céline Buchy1,*, Eberhard Frey2, Wolfgang Stinnesbeck3, and José Guadalupe López-Oliva4 1 Universität Karlsruhe, Geologisches Institut, Postfach 6980, D-76128 Karlsruhe, Germany. Current address: Museo del Desierto, Apartado Postal 307, 25000 Saltillo, Coahuila, Mexico. 2 Geowissenschaftliche Abteilung, Staatliches Museum für Naturkunde, Erbprinzenstrasse 13, D-76133 Karlsruhe, Germany. 3 Universität Karlsruhe, Geologisches Institut, Postfach 6980, D-76128 Karlsruhe, Germany. 4 Universidad Autónoma de Nuevo León, Facultad de Ciencias de la Tierra, Apartado Postal 104, 67700 Linares, N.L., Mexico. * [mcbuchy@myway.com](mcbuchy@myway.com) ABSTRACT We here describe the first mosasaur from Mexico known by significant cranial remains, from the late Early Maastrichtian Méndez Formation of Nuevo León, north-east Mexico. The specimen comprises a fragmentary skull and parts of the mandibles. Some anatomical features suggest a juvenile animal. The skull possesses a rostral tuberosity on the premaxilla, as well as a combination of features known from different mosasaur genera, like its frontopremaxillary suture situated caudal to the external naris, its prefrontal and postorbitofrontal being in contact lateral to the orbit, associated with the supra-and infrastapedial processes of its quadrate which almost contact one another. Despite being clearly distinct from any hitherto described mosasaur, the affinities of this specimen with other mosasaurs remain obscure, not only because of incompleteness, but also because of the poorly understood biological significance of the characters used for the classification of Mosasauridae. Key words: Mosasauridae, Early Maastrichtian, Méndez Formation, north-east Mexico. RESUMEN Se describe el primer mosasauro conocido por restos de cráneo deMéxico, de la FormaciónMéndez, del final del Maastrichtiano Temprano, de Nuevo León, noreste de México. El espécimen comprende un cráneo fragmentado y partes de las mandíbulas. Diversas estructuras anatómicas sugieren que este era un animal joven. El cráneo tiene una protuberancia rostral en la premaxila, así como una combinaciónde estructuras conocidas de diferentes géneros de mosasauros, entre ellas, la sutura frontopremaxilarsituada caudalmente a su nariz, el prefrontal y postorbitofrontal están en contacto lateral con la órbita, asociados con los procesos supra e infrastapedial desu cuadrado, los cuales tienen un ligero contacto entre sí. Apesar de ser claramente distintos de cualquier otro mosasauro descrito hasta ahora, las afinidades de este espécimen con otros mosasauros permanecen inciertas, no solamente debido a lo incompleto, sino tambiénporque la significancia biológica de los caracteres utilizados para la clasificación de los mosasauros (Mosasauridae) está pobremente entendida. Palabras clave: Mosasauridae, Maastrichtiano Temprano, Formación Méndez, noreste de México. 90 Buchy et al. INTRODUCTION Mosasaurs were Upper Cretaceous marine lizards with possible varanoid affinities (De Braga and Carroll, 1993; Caldwell et al., 1995; Bell, 1997a; Zaher and Rieppel, 1999; Evans et al. , 2006) . Currently, all mosasaurs are grouped within Mosasauridae (Bell, 1997b). Until recently, Mosasauridae was conceived of as a morphologically homogeneous group, and the classification of Williston (1895, 1897) separating three subfamilies had not been profoundly modified by subsequent analyses (Russell, 1967; De Braga and Carroll, 1993; Bell, 1997b). However, Bell and Polcyn (2005) recently suggested that fin-like limbs evolved at least twice within mosasauroids. Should their results be supported by further analyses, our understanding of the relationships within the group might change drastically. Mosasaurs are known worldwide and are especially ab

FAQs

Where and from which formation was the mosasaur specimen discovered?

The specimen comes from the late Early Maastrichtian Méndez Formation in Nuevo León, north-east Mexico.

What parts of the mosasaur are included in the study?

The fossil comprises a fragmentary skull and parts of the mandibles.

Why are the specimen’s relationships to other mosasaurs still unclear?

Affinities remain obscure because the material is incomplete and because the biological significance of characters used for Mosasauridae classification is poorly understood.

Aug 27, 2026

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