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Temporal fenestra in Mesosaurus

A new skull reconstruction for *Mesosaurus*, including a temporal fenestra !

Piñeiro G., Ferigolo J., Ramos A.&  Laurin M. In press. Cranial morphology
of the Early Permian mesosaurid *Mesosaurus tenuidens* and the evolution of
the lower temporal fenestration reassessed. Comptes Rendus Palevol.



The Early Permian mesosaurids are the oldest known aquatic amniotes with an
exclusively Gondwanan distribution. Although several hundred of
complete skeletons have been discovered and intensively studied, the
anatomy and taxonomic composition of the group, as well as its
phylogenetic relationships remain controversial. Several well-preserved
mesosaurid specimens found in Uruguay justify a new anatomical
reconstruction of the skull of Mesosaurus tenuidens, differing
from earlier ones especially in the presence of a lower temporal
fenestra. The significance of this structure for the evolution of
temporal fenestration in amniotes is evaluated according to the two most
 recent phylogenetic hypotheses, in which mesosaurids are basalmost
sauropsids or basalmost parareptiles. A synapsid-like fenestration may
be the primitive condition for Amniota, and it may be also a basal
condition for parareptiles, because recent phylogenies suggest a basal
position for mesosaurids and lanthanosuchoids within that group, and
both possess a lower temporal fenestra. Our results also give a
moderately strengthened support for diapsid affinities of turtles.