Nothosaurus is a sauropterygian taxon known by several species, whose fossils have been found in the Middle and lower Upper Triassic of Europe, China, Israel and Tunisia (Rieppel and Wild, 1996; Rieppel et al.
those from Royuela, Siles and Puente Genave-Villarodrigo), implies the presence of, at least, two different species of the sauropterygian Nothosaurus in the Middle Triassic of the Iberian Peninsula.
2003): A new species of the sauropterygian genus Nothosaurus from the lower Muschelkalk of Winterswijk, The Netherlands.
Sauropterygians are unique animals to study because they belong to a diverse taxon of aquatic reptiles that evolved from terrestrial ancestors soon after the end-Permian extinction and flourished during the Mesozoic period before they became extinct at the end of that era.
They were one of the first completely marine reptiles and different species of Sauropterygians are united by a radical adaptation of their pectoral girdle - a bone and muscle system found behind the head that supports the upper body limbs in animals - which helped the creature make powerful flipper strokes most famously recognized in species such as pliosaurs.
Mosasaurs, sauropterygians, and ichthyosaurs invaded the Mesozoic seas between 251 million and 100 million years ago.
Since the fossilized remains of pregnant mosasaurs, sauropterygians, and ichthyosaurs show that these species gave birth to live young, they must also have employed genetic sex determination, a point on which the fossil record is silent.