A new rhynchocephalian from the late jurassic of Germany with a dentition that is unique amongst tetrapods.

Rhynchocephalians, the sister group of squamates (lizards and snakes), are only represented by the single genus Sphenodon today. This taxon is often considered to represent a very conservative lineage. However, rhynchocephalians were common during the late Triassic to latest Jurassic periods, but rapidly declined afterwards, which is generally attributed to their supposedly adaptive inferiority to squamates and/or Mesozoic mammals, which radiated at that time. New finds of Mesozoic rhynchocephalians can thus provide important new information on the evolutionary history of the group. A new fossil relative of Sphenodon from the latest Jurassic of southern Germany, Oenosaurus muehlheimensis gen. et sp. nov., presents a dentition that is unique amongst tetrapods. The dentition of this taxon consists of massive, continuously growing tooth plates, probably indicating a crushing dentition, thus representing a previously unknown trophic 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

Comparative study of sperm ultrastructure of five species of teiid lizards (Teiidae, Squamata), and Cercosaura ocellata (Gymnophthalmidae, Squamata)

Sperm ultrastructure of five teiid lizards (Callopistes flavipunctatus, Crocodilurus amazonicus, Dicrodon guttulatum, Dracaena guianensis, and Teius oculatus), and the gymnophthalmid Cercosaura ocellata is described for the first time. Comparisons of sperm ultrastructure among these species and with those of previously examined teiids and gymnophthalmids revealed that the two groups of Teiioidea (Gymnophthalmidae and Teiidae), and the two subfamilies of Teiidae (Teiinae and Tupinambinae) could be distinguished on the basis of sperm ultrastructure data. Significant differences in sperm dimensions between Cnemidophorus and Aspidoscelis support the recent splitting of these two lineages into different genera. Our results revealed high levels of inter-generic variability in sperm ultrastructure within Teiidae, which produces a data set useful in analyzing relationships between genera and families. In phylogenetic analyses, however, sampling multiple species within teiid genera is essential and recording sperm measurements may profitably complement qualitative ultrastructural characters, maximizing the information content of these structures. (c) 2007 Published by Elsevier Ltd