ANKYLOSAURIAN TAIL CLUBS OF MIDDLE CAMPANIAN TO EARLY MAASTRICHTIAN AGE FROM WESTERN NORTH-AMERICA, WITH DESCRIPTION OF A TINY CLUB FROM ALBERTA AND DISCUSSION OF TAIL ORIENTATION AND TAIL CLUB FUNCTION

There are numerous undescribed tail clubs of diverse morphologies that may be assigned to Euoplocephalus (Ornithischia, Thyreophora, Ankylos auridae) of middle Campanian to early Maastrichtian age. Among these i s an exceptionally small club, the smallest so far described from Nort h America. Most, but not all, clubs can be placed into one of three sh ape categories: round, bluntly pointed, or elongate. Much of this dive rsity is ontogenetic or individual, but some of it may be taxonomic. C audal structure restricts lateral, and especially vertical, tail flexi bility. Analysis of hindlimb length, tail length, and downward angle o f the tail from the hips suggests that the tail was normally carried a nd swung just above the ground, and was used primarily defensively, fo r striking at the metatarsals of an attacking theropod. Intraspecific, agonistic functions are possible, but improbable.