JUDITH RIVER NORTH: DINOSAUR BIOSTRATIGRAPHY OF THE FOREMOST AND OLDMAN FORMATION IN SOUTHEASTERN ALBERTA, CANADA

The Judith River Formation (JRF) of Montana extends north into Canada where it is recognized as the Foremost and Oldman formations (the lower Belly River Group; BRG). The best exposures of these units are adjacent to the Milk River, in SE Alberta. Although known to produce dinosaur fossils for over a century, these units have been comparatively poorly documented relative to the upper BRG (Dinosaur Park Formation; DPF). For the last decade, the Southern Alberta Dinosaur Project of the Royal Ontario Museum and the Cleveland Museum of Natural History has documented the fauna and biostratigraphy of the lower BRG in the Milk River region. The project has resulted in the collection of over 5000 new dinosaur specimens; new data on dinosaur biostratigraphy is summarized here for the first time.

The Foremost Formation has produced limited material, with only two dinosaur taxa known from diagnostic cranial material: the basal centrosaurine Xenoceratops foremostensis and the pachycephalosaurid Colepiocephale lambei. The latter taxon also occurs in the time-equivalent section of the JRF in Kennedy Coulee, MT.

The Oldman Formation consists of three successive units, 1) a lower mudstone-dominated unit, 2) a middle sand-dominated unit, and 3) an upper muddy unit. Our work has revealed that each of the three units hosts a distinct ornithischian fauna. The lower unit has yeilded a bonebed of the hadrosaurid Gryposaurus, and specimens of the basal centrosaurines Albertacertatops nesmoi and an unnamed new taxon. The middle unit correlates to the JRF in the region of Malta, MT; both regions have produced multiple skeletons Brachylophosaurus canadensis. The upper unit has produced the most diagnostic specimens, including Euoplocephalus, Daspletosaurus nov. sp., and Saurornitholestes. Ceratopsid fossils are particularly abundant, and include several monodominant Centrosaurus apertus bonebeds, along with chasmosaurine material assignable to Chasmosaurus and Anchiceratops. The fauna of the upper unit is similar to that of the lower DPF at Dinosaur Provincial Park, and supports the regional distribution of dinosaur faunal zones proposed previously.

The next phase of the project is to assemble data from Montana into this framework, in order to evaluate dinosaur faunal turnover mechanisms on a high-resolution regional scale.