A NEW SPECIES OF BAENID TURTLE FROM THE KAIPAROWITS FORMATION (UPPER CRETACEOUS, CAMPANIAN) OF SOUTHERN UTAH

摘要

Newly discovered baenid turtle specimens from the middle Campanian Kaiparowits Formation of southern Utah are described herein as a new taxon, Arvinachelys goldeni, gen. et sp. nov. The holotype consists of a nearly complete articulated skeleton and shell. The skull was scanned using micro-computed tomography (CT) to gain a better understanding of its internal anatomy. This baenid possesses two distinct external nares almost completely separated by a dorsal projection of the premaxillae and a ventral extension of the nasals, an autapomorphic feature among known baenid taxa. The skull is wedge-shaped with a broad rostrum and laterally expanded nasals. The importance of skull/shell associations is exemplified by Arvinachelys goldeni, because isolated shells attributable to this taxon had previously been assigned to the genus Plesiobaena, whereas phylogenetic analysis of more complete material supports a sister relationship with the Maastrichtian taxon Hayemys latifrons. These taxa are relatively basal within the Baenodda, a nested clade within Baenidae. The general shell morphology exhibited by Plesiobaena antiqua, Peckemys brinkman, and Palatobaena cohen was previously hypothesized to support a monophyletic clade that included those three taxa, along with Cedrobaena putorius, Gamerabaena sonsalla, Palatobaena bairdi, and Palatobaena gaffneyi. However, the inclusion of Arvinachelys goldeni, gen. et sp. nov., in a phylogenetic analysis of Baenidae indicates that the character states exhibited by those taxa are representative of plesiomorphic states within Baenodda, and the phylogenetic relationships within this clade are in need of reevaluation.