title: Peculiar macrophagous adaptations in a new Cretaceous pliosaurid.
abstract: During the Middle and Late Jurassic, pliosaurid plesiosaurs evolved gigantic body size and a series of craniodental adaptations that have been linked to the occupation of an apex predator niche. Cretaceous pliosaurids (i.e. Brachaucheninae) depart from this morphology, being slightly smaller and lacking the macrophagous adaptations seen in earlier forms. However, the fossil record of Early Cretaceous pliosaurids is poor, concealing the evolution and ecological diversity of the group. Here, we report a new pliosaurid from the Late Hauterivian (Early Cretaceous) of Russia. Phylogenetic analyses using reduced consensus methods recover it as the basalmost brachauchenine. This pliosaurid is smaller than other derived pliosaurids, has tooth alveoli clustered in pairs and possesses trihedral teeth with complex serrated carinae. Maximum-likelihood ancestral state reconstruction suggests early brachauchenines retained trihedral teeth from their ancestors, but modified this feature in a unique way, convergent with macrophagous archosaurs or sphenacodontoids. Our findings indicate that Early Cretaceous marine reptile teeth with serrated carinae cannot be unequivocally assigned to metriorhynchoid crocodylomorphs. Furthermore, they extend the known diversity of dental adaptations seen in Sauropterygia, the longest lived clade of marine tetrapods.
authors.affiliation: Department of Earth SciencesUniversity of OxfordOxford OX1 3AN, UK; Department of GeologyUniversité de Liège14 allée du 6 Août, Liège 4000, Belgium.
authors.forename: Valentin
authors.identifier: 0000-0002-8808-6747
authors.initials: V
authors.lastname: Fischer
authors.affiliation: Ecological FacultySaratov State Technical UniversityPolitekhnicheskaya Ul. 77, Saratov 410054, Russia; Geological FacultySaratov State UniversityAstrakhanskaya Ul. 83, Saratov 410012, Russia.
authors.forename: Maxim S
authors.initials: MS
authors.lastname: Arkhangelsky
authors.affiliation: I.A. Goncharov Ulyanovsk Regional Natural History Museum Boulevard Novyi Venets 3/4 Ulyanovsk 432000, Russia.
authors.forename: Ilya M
authors.initials: IM
authors.lastname: Stenshin
authors.affiliation: Natural Science Museum Ulyanovsk State University Ulyanovsk, Russia.
authors.forename: Gleb N
authors.initials: GN
authors.lastname: Uspensky
authors.affiliation: Lomonosov Moscow State University Leninskie Gory 1 GSP-1, Moscow 119991, Russia.
authors.forename: Nikolay G
authors.initials: NG
authors.lastname: Zverkov
authors.affiliation: Department of Earth Sciences University of Oxford Oxford OX1 3AN, UK.
authors.forename: Roger B J
authors.identifier: 0000-0001-8244-6177
authors.initials: RB
authors.lastname: Benson
keywords: Cretaceous; Makhaira rossica; Plesiosauria; Pliosauridae; convergence; macrophagy