Plesiosaurs were large, fully marine reptiles from the Jurassic and Cretaceous, with both fore- and hind-limbs modified into large flippers. They evolved from the Triassic Nothosaurs, Crocodile-like semi-aquatic reptiles related to Lizards, and persisted as a numerous and diverse group until the end of the Cretaceous.
In 1897-8 the French palaeontologist Henri Émile Sauvage described a partial Plesiosaur skull and mandible (specimen number MG33 at the Geological Museum in Lisbon) from the Early Jurassic São Gião Formation (technically Toarcian, 183-175.6 million years old) of Alhadas in Central Portugal, as Plesiosaurus sp., but refined from any more detailed classification.
In a paper published in the journal Acta Palaeontologica Polonica on 20 May 2012, Adam Smith of the Birmingham Science Museum, Ricardo Araújo of the Roy M. Huffington Department of Earth Sciences at Southern Methodist University and the Museu da Lourinhã and Octávio Mateus of the Centro de Investigação em Ciência e Engenharia Geológica at the Faculdade de Ciências e Tecnologia at the Universidade Nova de Lisboa and the Museu da Lourinhã, redescribe and formally name MG33.
Specimen MG33 in (A) right lateral, (B) left lateral, (C) dorsal, and (D) ventral views; (1) photographs, (2) interpretive drawings. Smith et al. (2012).
Smith et al. conclude that MG33 is an Elasmosaur, a member of a group of Plesiosaurs that evolved exceptionally long necks and reached lengths of between 3 and 14 m. They formally name the specimen as Lusonectes sauvagei, Sauvage's Portuguese swimmer.
See also An Early Jurassic Pliosaur from Normandy, A Pregnant Plesiosaur, The Weymouth Pliosaur and Reptiles on Sciency Thoughts YouTube.
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