biostudies-literatureUnknown25(10)Persons WSPlesiosaurs are a group of Mesozoic marine diapsids. Most derived plesiosaurs fall into one of two typical body forms: those with proportionately small heads, short snouts, and elongated necks, and those with large heads, elongated snouts, and short necks. <i>Serpentisuchops pfisterae</i> is a polycotylid plesiosaur from the Upper Cretaceous Pierre Shale that presents the trait combination of both an elongate snout and elongate neck (consisting of 32 vertebrae). Phylogenetic analysis places <i>Serpentisuchops</i> within the Polycotylinae, indicating that its long snout is an ancestral trait, while its long neck is secondarily derived and convergent with that of ancestral plesiosaurs, contemporaneous elasmosaurids, and some more basal members of the Polycotylidae. The conical, recurved, andiScience105033https://www.ebi.ac.uk/biostudies/studies/S-EPMC9617461biostudies-literatureA long-snouted and long-necked polycotylid plesiosaur from the Late Cretaceous of North America.PMC9617461Kelley AStreet HPPersons WSfalseA long-snouted and long-necked polycotylid plesiosaur from the Late Cretaceous of North America.Plesiosaurs are a group of Mesozoic marine diapsids. Most derived plesiosaurs fall into one of two typical body forms: those with proportionately small heads, short snouts, and elongated necks, and those with large heads, elongated snouts, and short necks. <i>Serpentisuchops pfisterae</i> is a polycotylid plesiosaur from the Upper Cretaceous Pierre Shale that presents the trait combination of both an elongate snout and elongate neck (consisting of 32 vertebrae). Phylogenetic analysis places <i>Serpentisuchops</i> within the Polycotylinae, indicating that its long snout is an ancestral trait, while its long neck is secondarily derived and convergent with that of ancestral plesiosaurs, contemporaneous elasmosaurids, and some more basal members of the Polycotylidae. The conical, recurved, and2022-01-01T00:00:00Z2022 Oct2025-04-04T09:41:40.319Z2025-04-04T09:41:40.319ZS-EPMC96174613631716110.1016/j.isci.2022.105033