A “beaded” sphenodontian (Diapsida: Lepidosauria) from the Early Cretaceous of central Mexico

ABSTRACT

The Albian sphenodontian Pamizinsaurus tlayuaensis, gen. et sp. nov., from the Tlayua Quarry, Central Mexico, is described. The holotype is a posthatchling characterized by the presence of rows of small rounded osteoderms transversally oriented, relatively few hatchling teeth each with well-developed ridges, and a posteriorly displaced ventral process of the mandibular symphysis at an early ontogenetic stage. A small retroarticular process, long central region of the pterygoid, and the narrowness of the posterior end of the interpterygoid vacuity suggest sister-group relationships with sphenodontines + eilenodontines. The conspicuous dermal skeleton is similar to that of helodermatids, suggesting that it could have served to protect against predation in open environments. This unique structure argues against the idea of low morphological diversity within sphenodontians. Pamizinsaurus is the latest occurring fossil sphenodontian.