Agriodontosaurus
Agriodontosaurus is an extinct genus of early rhynchocephalian reptiles known from the Middle Triassic Helsby Sandstone Formation of England. The genus contains a single species, Agriodontosaurus helsbypetrae, known from a partial skull and skeleton. It is the oldest known definitive rhynchocephalian and currently the oldest known member of Lepidosauria, the broader group including the modern tuatara and snakes and lizards.
Discovery and naming
The Agriodontosaurus holotype specimen, BRSUG 29950-14, was discovered excavated by Robert A. Coram in 2015 in a sandstone bed representing the Pennington Point Member of the Helsby Sandstone Formation in Sidmouth, Devon, South West England. Natural weathering had exposed part of the specimen's dorsal surface when it was collected, and later physical preparation was carried out to reveal more of the anatomy. The specimen, which remains fully contained in the sandstone block it was collected in, is well preserved and partially articulated. It comprises much of the mandible and skull, although it is distorted and missing the rostrum and much of the right side, in addition to an articulated series of eight cervical vertebrae and the succeeding few dorsal vertebrae, various disarticulated dorsosacral, sacral, and caudal vertebrae, a complete left pectoral girdle and parts of the right one, forelimb bones, most of the pelvic girdle, and hindlimb bones.In 2025, Marke and colleagues described Agriodontosaurus helsbypetrae as a new genus and species of early rhynchocephalians based on these fossil remains. The generic name, Agriodontosaurus, combines a reference to Agrionius, an Ancient Greek epithet of the god Dionysus, with the Greek words donto, meaning, and σαῦρος, meaning. The specific name, helsbypetrae, references the discovery of the specimen in the Helsby Sandstone Formation, combined with the latinized Greek petra, meaning.