An unusual microsite from the Upper Cretaceous Horseshoe Canyon Formation of Alberta, Canada

Abstract

ABSTRACT The Upper Cretaceous Horseshoe Canyon Formation of Alberta, Canada, is among the best-studied paleoecosystems in North America. However, its microvertebrate paleocommunity structure is relatively poorly known, partly because it lacks the abundant microsites of other Upper Cretaceous deposits of Alberta. An unusual microsite (FTS-2) from the Horsethief Member of the Horseshoe Canyon Formation is described that produces abundant anuran and troodontid material, alongside perinatal material from ornithischians and tyrannosaurs. Anuran specimens representing a minimum of two separate taxa and a metatherian molar suggest that these components of the fauna were more diverse than currently recognized. The assemblage is similar to three other North American sites that produce abundant troodontid teeth alongside perinatal dinosaurs. However, environmental and taphonomic conditions of these sites vary, supporting the notion of mixed biotic and abiotic factors driving the association of troodontids alongside perinates. In part, this may stem from similar nesting preferences between troodontids and other dinosaurs, as material collected from all three sites suggests proximity to troodontid nesting sites. Sites such as FTS-2 are important for revealing the rare and small components of paleoecosystems, and hold promise for revealing interactions between these parts of the fauna.