Taphonomy of and new burrows from Oryctodromeus cubicularis, a burrowing neornithischian dinosaur, from the mid-Cretaceous (Albian-Cenomanian) of Idaho and Montana, U.S.A.

Abstract Vertebrate assemblages from the mid-Cretaceous (Albian-Cenomanian) Wayan Formation of Idaho and Vaughn Member of the Blackleaf Formation of Montana are dominated by the small burrowing dinosaur, Oryctodromeus cubicularis . Specimens can be assigned to three distinct taphofacies dependent on degrees of skeletal articulation and associated lithofacies. Taphofacies A comprises mostly to fully articulated specimens in bioturbated sandstones. Taphofacies B comprises partially articulated to associated collections of skeletal elements in pedogenic mudstones, siltstones, and fine-grained sandstones. Taphofacies C comprises isolated skeletal elements within the debris-flow deposit of the Robison Bonebed. Except for one associated nodosaur skeleton, Oryctodromeus is the only vertebrate represented by significant associations of skeletal elements or portions of articulated skeletal elements within the Wayan Formation/Vaughn Member units, and occurrences represent a paleocommunity dominated by a small cursorial and fossorial vertebrate. The co-occurrence of multiple individuals, representing presumed juvenile and adult growth stages, reinforce previous suggestions of parental care in this species. In addition, newly reported Oryctodromeus burrows compare in overall morphology and size with the burrow containing the holotype of Oryctodromeus . These data suggest the possibility that evidence for additional fossil taxa having had a communal and fossorial lifestyle may be discerned through further focused taphonomic investigations.