LATE EARLY JURASSIC MAMMALIAFORMS FROM HUIZACHAL CANYON, TAMAULIPAS, MEXICO

Previous reports of the fossil vertebrates from the upper Lower Jurassic La Boca Formation of Tamaulipas, Mexico, presented descriptions of a tritylodontid therapsid, a burrowing diapsid, crocodyliforms, a pterosaur and sphenodontians. Mammaliaform material is rare, consisting primarily of partial lower jaws, some of which are extremely small. Five partial dentaries and one maxilla all have molars of triconodont morphology. Two lower jaws clearly show the internal mandibular trough, suggesting attachment of postdentary bones, another two do not possess a trough, and in another its presence or absence cannot be determined. This diversity of forms suggests that during the late Early Jurassic variations on the primitive triconodont molar patterns and in lower jaw morphology took place. The mammaliaform specimens from Tamaulipas appear to represent new taxa, but, because of the incomplete preservation of most of the material, only three new genera and species are erected: Bocaconodon tamaulipensis, Victoriaconodon inaequalis, and Huasteconodon wiblei.