Pahasapasaurus gillettei, new polycotylid species from Upper Cretaceous of Utah
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Ben Creisler
Nov 26, 2025, 12:08:06 AM (yesterday) Nov 26
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Ben Creisler
A new paper:
Pahasapasaurus gillettei sp. nov.,
Rebecca L. Schmeisser McKean (2025)
A new species of Pahasapasaurus (Plesiosauria: Polycotylidae) from the Upper Cretaceous Tropic Shale (lower Turonian) of southern Utah, U.S.A.
Cretaceous Research 106269
doi: https://doi.org/10.1016/j.cretres.2025.106269
https://www.sciencedirect.com/science/article/abs/pii/S0195667125001922
Highlights
Polycotylid plesiosaurs originated in the Cretaceous Western Interior Seaway
The fauna of the Tropic Shale includes six known genera of short-neck plesiosaurs
Pahasapasaurus is unique among polycotylid plesiosaurs in having a closed palate
A new species of Pahasapasaurus, P. gillettei, possesses teeth with smooth crowns
Abstract
The Tropic Shale is an Upper Cretaceous (Cenomanian–Turonian) formation that was deposited along the western side of the Cretaceous Western Interior Seaway. The biodiversity within the Tropic Shale is high, with marine organisms including ammonoids, bivalves (clams, oysters), gastropods, actinopterygians, chondrichthyans, turtles, mosasaurs, and plesiosaurs. This paper describes a new polycotylid plesiosaur, Pahasapasaurus gillettei sp. nov., based on a well-preserved, partial skeleton from the Tropic Shale of southern Utah, U.S.A. Several characteristics from this specimen are shared with the genus Pahasapasaurus, including the morphology of the palate (lack of an anterior interpterygoid vacuity, a robust parasphenoid with ventral keel), an elongated temporal fenestra, a low tooth count in the mandibular symphysis, and the lack of a posterodistal expansion of the humerus. Pahasapasaurus gillettei is distinct in possessing teeth with smooth enamel, a posterior extension of the squamosals along the midline, a low maxillary tooth count, a small posterolateral extension of the coracoid, as well as a unique combination of characters. Pahasapasaurus was previously known from a single species (P. haasi) from the upper Cenomanian Greenhorn Limestone of South Dakota, U.S.A., deposited along the eastern side of the Western Interior Seaway. The discovery of P. gillettei extends the known range of the genus Pahasapasaurus into slightly younger (lower Turonian) sediments along the opposite side of the seaway and has implications for the evolutionary history of polycotylid plesiosaurs. Pahasapasaurus gillettei also adds a sixth species of short-neck plesiosaur to the Tropic Shale, expanding the known biodiversity of this productive formation.
Rebecca L. Schmeisser McKean (2025)
A new species of Pahasapasaurus (Plesiosauria: Polycotylidae) from the Upper Cretaceous Tropic Shale (lower Turonian) of southern Utah, U.S.A.
Cretaceous Research 106269
doi: https://doi.org/10.1016/j.cretres.2025.106269
https://www.sciencedirect.com/science/article/abs/pii/S0195667125001922
Highlights
Polycotylid plesiosaurs originated in the Cretaceous Western Interior Seaway
The fauna of the Tropic Shale includes six known genera of short-neck plesiosaurs
Pahasapasaurus is unique among polycotylid plesiosaurs in having a closed palate
A new species of Pahasapasaurus, P. gillettei, possesses teeth with smooth crowns
Abstract
The Tropic Shale is an Upper Cretaceous (Cenomanian–Turonian) formation that was deposited along the western side of the Cretaceous Western Interior Seaway. The biodiversity within the Tropic Shale is high, with marine organisms including ammonoids, bivalves (clams, oysters), gastropods, actinopterygians, chondrichthyans, turtles, mosasaurs, and plesiosaurs. This paper describes a new polycotylid plesiosaur, Pahasapasaurus gillettei sp. nov., based on a well-preserved, partial skeleton from the Tropic Shale of southern Utah, U.S.A. Several characteristics from this specimen are shared with the genus Pahasapasaurus, including the morphology of the palate (lack of an anterior interpterygoid vacuity, a robust parasphenoid with ventral keel), an elongated temporal fenestra, a low tooth count in the mandibular symphysis, and the lack of a posterodistal expansion of the humerus. Pahasapasaurus gillettei is distinct in possessing teeth with smooth enamel, a posterior extension of the squamosals along the midline, a low maxillary tooth count, a small posterolateral extension of the coracoid, as well as a unique combination of characters. Pahasapasaurus was previously known from a single species (P. haasi) from the upper Cenomanian Greenhorn Limestone of South Dakota, U.S.A., deposited along the eastern side of the Western Interior Seaway. The discovery of P. gillettei extends the known range of the genus Pahasapasaurus into slightly younger (lower Turonian) sediments along the opposite side of the seaway and has implications for the evolutionary history of polycotylid plesiosaurs. Pahasapasaurus gillettei also adds a sixth species of short-neck plesiosaur to the Tropic Shale, expanding the known biodiversity of this productive formation.
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