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Oenosaurus, new sphenodontian from Jurassic in Germany
From: Ben Creisler
Non-dino in PLoS ONE:
Oliver W. M. Rauhut, Alexander M. Heyng, Adriana López-Arbarello &
Andreas Hecker (2012)
A New Rhynchocephalian from the Late Jurassic of Germany with a
Dentition That Is Unique amongst Tetrapods.
PLoS ONE 7(10): e46839.
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.
Principle Findings [s/b Principal Findings]
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.