Rhynchocephalians (beakheads) form the sister group to the squamates (lizards and snakes) and are represented by the extant single genus Sphenodon (the tuataras) today. Beakheads are often considered to represent a very conservative lineage. However, rhynchocephalians were common from the late Triassic to late Jurassic, but the clade went into rapidly declined afterwards, a decline frequently attributed to the supposedly adaptive inferiority of the beakheads to squamates and Mesozoic mammals, which radiated at that time.
Rauhut et al. (2012) report a new fossil rhynchocephalian from the late Jurassic of southern Germany, teeth of this new animal consists of massive, continuously growing plates, suggesting a device for crushing food, a previously unknown feeding adaptation in rhynchocephalians.
The evolution of the extraordinary dentition of Oenosaurus from the already highly specialized Zahnanlage generally present in derived rhynchocephalians demonstrates an unexpected evolutionary plasticity of these animals. Together with other lines of evidence, this seriously casts doubts on the assumption that rhynchocephalians are a conservative and adaptively inferior lineage. Furthermore, the new taxon underlines the high morphological and ecological diversity of rhynchocephalians in the latest Jurassic of Europe, just before the decline of this lineage on this continent. Thus, selection pressure by radiating squamates or Mesozoic mammals alone might not be sufficient to explain the demise of the clade in the Late Mesozoic, and climate change in the course of the fragmentation of the supercontinent of Pangaea might have played a major role.
Roland Pöschl, found the 146 million year old fossil, and the owners and operators of the Krautworst Naturstein quarry, Ulrich Leonhardt, Roland Pöschl and Uwe Krautworst, donated the specimen to the Staatssammlung für Paläontologie und Geologie in Munich.
