Ceratopsid dinosaurs from the Upper Cretaceous Almond Formation of southwestern Wyoming

Abstract

The 1937 American Museum of Natural History (AMNH)–Sinclair Oil Company joint expedition to the late Campanian and early Maastrichtian Almond Formation of the Rock Springs Uplift, southern Wyoming, recovered two ceratopsid cranial specimens. AMNH 3652, a partial skull lacking the frill, is characterized by elongate, procurving postorbital horns and a deep rostrum. Although the specimen cannot be identified to the generic or specific level, it appears to be closely related to the clade of chasmosaurine ceratopsids including Anchiceratops, Arrhinoceratops, Diceratops, Torosaurus , and Triceratops , exclusive of Pentaceratops and Chasmosaurus . AMNH 3656, a frill fragment, is characterized by large, triangular marginal processes and an average thickness in excess of 40 mm. This specimen is similar to previously reported frills from Anchiceratops . The ceratopsid specimens from the Almond Formation are significant because they represent two early occurrences of chasmosaurine ceratopsids as well as a unique occurrence in southern Wyoming. Present address: Department of Anatomical Sciences, Stony Brook University, Stony Brook, NY 11794, U.S.A. email: afarke{at}ic.sunysb.edu