title: The Braincase and Endosseous Labyrinth of Plioplatecarpus peckensis (Mosasauridae, Plioplatecarpinae), With Functional Implications for Locomotor Behavior.
abstract: Adaptations of mosasaurs to the aquatic realm have been extensively studied from the perspective of modifications to the post-cranial skeleton. In recent years, imaging techniques such as computed tomography have permitted the acquisition of anatomical data from previously inaccessible sources. An exquisitely preserved specimen of the plioplatecarpine mosasaur Plioplatecarpus peckensis presents an opportunity to examine the detailed structure of the braincase, as well as the form of the otic capsule endocast. These data elaborate upon previous descriptions of the braincase of Plioplatecarpus, and provide a detailed, three dimensional reconstruction of the osseous labyrinth for the first time. The otic capsule endocasts reveal that the size of the labyrinth relative to head size is comparable to that of other squamates, suggesting that labyrinth size was not a factor in increasing sensitivity. However, all three semicircular canals are tall and strongly arced to a degree comparable to, and even exceeding, that observed in arboreal and aquatic lizards. Comparison of the sensitivity of the canals in each of the three major axes of rotation suggests Plioplatecarpus peckensis may have been most sensitive to movements in the pitch axis. Although early mosasaurs were probably anguilliform swimmers, most are thought to have been subcarangiform to thunniform locomotors with a near-rigid body form and likely decreased maneuverability. The data from the labyrinth presented here add a potential new dimension to this model of locomotion for further consideration, wherein changes in orientation, such as pitch, may have been more common locomotor behaviors than previously thought.
authors.affiliation: Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada, T2N 1N4.
authors.forename: Robin S
authors.initials: RS
authors.lastname: Cuthbertson
authors.affiliation: Department of Earth Sciences, Carleton University, Ottawa, Ontario, Canada, K1S 5B6.
authors.forename: Hillary C
authors.initials: HC
authors.lastname: Maddin
authors.affiliation: Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada, T6G 2E9.
authors.forename: Robert B
authors.initials: RB
authors.lastname: Holmes
authors.affiliation: Department of Comparative Biology and Experimental Medicine, University of Calgary, Calgary, Alberta, Canada, T2N 4N1.
authors.forename: Jason S
authors.initials: JS
authors.lastname: Anderson
mesh_terms: D000222:Adaptation, Physiological; D059925:Anatomic Landmarks; D000818:Animals; D001522:Behavior, Animal; D005075:Biological Evolution; D002508:Cephalometry / Q000379:methods; D004242:Diving; D007758:Ear, Inner / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000502:physiology*; D053476:Extinction, Biological; D005580:Fossils; D021621:Imaging, Three-Dimensional; D008116:Lizards / Q000033:anatomy & histology / Q000502:physiology*; D008953:Models, Anatomic; D009043:Motor Activity; D010802:Phylogeny; D012886:Skull / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000502:physiology*; D013550:Swimming; D055114:X-Ray Microtomography
keywords: acrobatic diving; locomotion; sensory evolution; swimming