Duba wurin da ke ƙasa sannan ka amsa tambayar daga baya a cikin harshe ɗaya kamar yadda wurin yake:  Passage: Plesiosauroids sun samo asali ne daga baya, irin wannan nau'i kamar pistosaurs. Akwai iyalai da yawa na plesiosauroids, waɗanda ke riƙe da bayyanar iri ɗaya kuma an bambanta su da takamaiman bayanai daban-daban. Waɗannan sun haɗa da Plesiosauridae, nau'ikan da ba su da ƙwarewa waɗanda aka iyakance su zuwa farkon zamanin Jurassic; Cryptoclididae, (misali Cryptoclidus), tare da matsakaiciyar wuyansa mai tsayi da ɗan ƙaramin gini; Elasmosauridae, tare da tsayi, wuyansa mai sassauƙa da ƙananan kawuna; da Cimoliasauridae, ƙungiyar da ba a san ta da ƙananan siffofin Cretaceous. Dangane da rarrabuwa na gargajiya, duk plesiosauroids suna da ƙaramin kai da dogon wuyansa amma, a cikin rarrabuwa na kwanan nan, an haɗa ƙungiyar Cretaceous mai gajeren wuyansa da babban kai, Polycotylidae, a ƙarƙashin Plesiosauroidea, maimakon ƙarƙashin Pliosauroidea na gargajiya. Girman plesiosaurs daban-daban sun bambanta sosai, tare da kimanin tsawon Trinacromerum yana da mita uku kuma Mauisaurus yana girma zuwa mita ashirin.  Tambaya: Wace kalma ce ta kasance kafin Plesiosauroids?
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