VERTEBRATE FAUNA OF THE MID-CRETACEOUS (ALBIAN) WAYAN FORMATION OF IDAHO, A POSSIBLE CORRELATE TO THE UPPER CEDAR MOUNTAIN FORMATION

Preliminary work in the middle Albian Wayan Formation of eastern Idaho, roughly contemporaneous to the upper Ruby Ranch and Mussentuchit members of the Cedar Mountain Formation of Utah, has yielded a fragmentary but diverse vertebrate fauna. This fauna is dominated by hypsilophodontid ornithopods, known from several partial, semi-articulated skeletons. Other ornithischians present include Tenontosaurus or a Tenontosaurus-like iguanodont (isolated teeth); another probable ornithopod (associated caudal vertebrae); rare probable neoceratopsians (partial pelvic and caudal skeletons); and ankylosaurids (teeth and a partial skeleton). Saurischian elements include a pedal phalange and an unidentified limb bone end from large indeterminate theropods; possibly two dromaeosaurids are also known from isolated teeth. Eggshells (oofamily Elongatoolithidae) from several localities also represent theropod dinosaurs. Teeth and skeletal remains are referable to both large and small crocodilians. Additional vertebrate material includes turtle carapace, semionotid fish teeth and a scale. Non-vertebrate specimens include unionid bivalves; petrified wood; and foliage of angiosperms, conifers, and ferns.

Mudrock represents the primary lithology of the Wayan, with subordinate sandstones and conglomerates. Deposition occurred in a fluvial system characterized by meandering streams. Faunal elements typically occur in distinct facies. For example, hypsilophodont, dromaeosaur, and eggshell fossils typically occur in fine-grained mudstones and siltstones, often associated with carbonate nodules and caliches. In contrast, iguanodonts, ankylosaurs, and large theropods are known mainly from conglomeratic fluvial lag deposits.

Faunal elements are similar to those of the upper Cedar Mountain Formation, but differ in the greater abundance of hypsilophodontids. This apparent dominance may be ecologically based or reflect a preservational bias favoring the preservation of smaller organisms.