Transitional evolutionary forms and stratigraphic trends in chasmosaurine ceratopsid dinosaurs : evidence from the Campanian of New Mexico

Three new chasmosaurines from the Kirtland Formation (∼75.0 - 73.4 Ma), New Mexico, form morphological and stratigraphic intermediates betweenPentaceratops(∼74.7 - 75Ma, Fruitland Formation, New Mexico) andAnchiceratops(∼72 - 71Ma, Horseshoe Canyon Formation, Alberta). The new specimens exhibit gradual enclosure of the parietal embayment that characterizesPentaceratops, providing support for the phylogenetic hypothesis thatPentaceratopsandAnchiceratopsare closely related. This stepwise change of morphologic characters observed in chasmosaurine taxa that do not overlap stratigraphically is supportive of evolution by anagenesis. Recently published hypotheses that placePentaceratopsandAnchiceratopsinto separate clades are not supported. This phylogenetic relationship demonstrates unrestricted movement of large-bodied taxa between hitherto purported northern and southern provinces in the Late Campanian, weakening support for the hypothesis of extreme faunal provincialism in the Late Cretaceous Western Interior.