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Anguanax, new plesiosaur from Jurassic of Italy



Ben Creisler
bcreisler@gmail.com


A new paper:


Andrea Cau & Federico Fanti (2015)
High evolutionary rates and the origin of the Rosso Ammonitico
Veronese Formation (Middle-Upper Jurassic of Italy) reptiles.
Historical Biology (advance online publication)
DOI:10.1080/08912963.2015.1073726
http://www.tandfonline.com/doi/full/10.1080/08912963.2015.1073726#abstract


The fossil record of metriorhynchids and plesiosaurians from the Rosso
Ammonitico Veronese Formation (RAVFm, Middle–Upper Jurassic, Italy) is
represented by elements collected between the eighteenth and twentieth
centuries. All the metriorhynchid material is referred to the genus
Neptunidraco. The first RAVFm plesiosaurian material was collected in
the nineteenth century and referred to Plesiosaurus: elements are here
described and interpreted as a chimerical association of
crocodylomorph and plesiosaurian bones, providing the first
co-occurrence of these clades in the RAVFm. The second plesiosaurian
is the associated skeleton that we refer to Anguanax zignoi gen. et
sp. nov. Bayesian phylogenetic analysis confirms the basal geosaurine
affinities of Neptunidraco resulted by parsimony analysis. Using both
methods, Anguanax was recovered as a basal pliosaurid, sister group of
the clade including Marmornectes and Thalassophonea. Bayesian
inference methods indicate that both Italian lineages diverged from
other known lineages between 176 and 171 Mya, also showing divergence
rates significantly higher than any other representative of their
respective clades. We suggest a phase of rapid evolutionary adaptation
to deeper marine environments in the ancestors of the Rosso Ammonitico
Veronese reptiles as a response to the latest Liassic regressive
regime in Northern Tethys.