Duba wurin da ke ƙasa sannan ka amsa tambayar daga baya a cikin harshe ɗaya kamar yadda wurin yake:  Passage: Sauropterygians na farko sun bayyana kimanin shekaru miliyan 245 da suka gabata (Ma), a farkon zamanin Triassic: sauropterygian na farko da ke da cikakkiyar ma'auni na stratigraphic yana cikin rarrabuwa na Spathian na zamanin Olenekian a Kudancin China. Misalai na farko sun kasance ƙananan (kimanin 60 cm), dabbobi masu kama da lizard-kamar dabbobi tare da dogon lokaci (pachypleurosaurs), amma sun yi girma da sauri zuwa tsawon mita da yawa kuma sun yada cikin ruwa mai zurfi (nothosaurs). Triassic-Jurassic extinction event ya shafe su duka sai dai plesiosaurs. A lokacin farkon Jurassic, waɗannan sun bambanta cikin sauri zuwa duka plesiosaurs masu dogon wuyansa, da kuma manyan manyan manyan pliosaurs. Da farko, an yi tunanin cewa plesiosaurs da pliosaurs sune manyan dangi guda biyu waɗanda suka bi hanyoyi daban-daban na juyin halitta. Yanzu yana da alama cewa waɗannan su ne kawai morphotypes a cikin cewa duka nau'o'in sun samo asali sau da yawa, tare da wasu pliosaurs da suka samo asali daga kakannin plesiosaur, kuma a madadin haka.  Tambaya: A lokacin farkon Jurassic, an raba pliosaurs zuwa cikin kungiyoyi biyu?
plesiosaurs masu dogon wuyansa masu ƙananan kai, da kuma ƙananan wuyansa masu manyan kai