Data from: Peculiar macrophagous adaptations in a new Cretaceous pliosaurid

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.

在中侏罗世至晚侏罗世时期，上龙科蛇颈龙类（pliosaurid plesiosaurs）演化出了庞大的体型，以及一系列与占据顶级捕食者生态位相关的颅部与齿部适应性特征。白垩纪的上龙科类群（即短颈龙亚科Brachaucheninae）则脱离了这一形态模式：它们体型略小，且缺乏早期类群所具备的大型捕食适应性特征。然而，早白垩世上龙科类群的化石记录极为匮乏，掩盖了该类群的演化历程与生态多样性。本研究报道了一件产自俄罗斯早白垩世晚豪特里维阶（Late Hauterivian）的全新上龙科类群化石。采用简化共识法（reduced consensus methods）进行的系统发育分析显示，该物种是目前已知最基干的短颈龙亚科成员。该上龙类体型小于其他衍生型上龙科类群，其齿槽呈成对簇状排列，且拥有带有复杂锯齿脊的三棱齿。基于最大似然法（maximum-likelihood）的祖先状态重建（ancestral state reconstruction）结果显示，早期短颈龙亚科类群保留了其祖先的三棱齿特征，但以独特的方式对该特征进行了改造，这与大型捕食性主龙类（archosaurs）或楔齿龙形类（sphenacodontoids）的趋同演化特征一致。本研究结果表明，带有锯齿脊的早白垩世海洋爬行动物牙齿无法被明确归为中喙鳄形类（metriorhynchoid crocodylomorphs）所有。此外，该发现拓展了我们对鳍龙超目（Sauropterygia）——这一演化存续时间最长的海洋四足类支系——齿部适应性特征多样性的认知。