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

Abstract

There are numerous undescribed tail clubs of diverse morphologies that may be assigned to Euoplocephalus (Ornithischia, Thyreophora, Ankylosauridae) of middle Campanian to early Maastrichtian age. Among these is an exceptionally small club, the smallest so far described from North America. Most, but not all, clubs can be placed into one of three shape categories: round, bluntly pointed, or elongate. Much of this diversity is ontogenetic or individual, but some of it may be taxonomic. Caudal structure restricts lateral, and especially vertical, tail flexibility. Analysis of hindlimb length, tail length, and downward angle of the tail from the hips suggests that the tail was normally carried and swung just above the ground, and was used primarily defensively, for striking at the metatarsals of an attacking theropod. Intraspecific, agonistic functions are possible, but improbable.

Euoplocephalus tutus and the Diversity of Ankylosaurid Dinosaurs in the Late Cretaceous of Alberta, Canada, and Montana, USA

“…Descriptions of the postcrania of Euoplocephalus tutus by Coombs [6]–[10], Carpenter [3], Penkalski [13], and Arbour et al [24] include information on most, but not all, aspects of the postcranial skeleton; in particular, the pre-caudal vertebral series has received relatively little attention. As such, more detailed descriptions and comparisons of the postcrania of specimens referred to Euoplocephalus tutus are presented.…”

“…Although no skull was known for Dyoplosaurus acutosquameus or Scolosaurus cutleri , Coombs [4] reasoned that if only one ankylosaurid species was valid in the Campanian of North America, then these two species must be junior synonyms of Euoplocephalus tutus . Coombs maintained the synonymy of Anodontosaurus lambei , Dyoplosaurus acutosquameus , and Scolosaurus cutleri with Euoplocephalus tutus throughout his publications on ankylosaurid anatomy [5]–[10]. Features considered diagnostic of Euoplocephalus tutus by Coombs [4] included premaxillae that are not covered by expanded nasals, long and slit-like nostrils, a premaxillary width that is equal or greater than the width between the most posterior maxillary teeth, a palate that does not taper anteriorly, and squamosal horns that are less prominent than those in Ankylosaurus magniventris Brown, 1908 [28].…”

A new ankylosaurid from the late Cretaceous Two Medicine Formation of Montana, USA

“…It is a round (sensu Coombs 1995), average-sized knob measuring 320 mm wide. The keeled major osteoderms are offset to the dorsal side of the knob, giving the club a somewhat "elf-eared" (dorsolaterally pointed) outline in distal view, though not as pronounced as in some other clubs, e.g., AMNH 5245 and UALVP 16247 (Coombs 1995: fig. 2C; Arbour and Snively 2009: fig.…”

The socio-sexual behaviour of extant archosaurs: implications for understanding dinosaur behaviour

“…Gangloff (1995) further noted the possible dimorphic nature of cranial proportions and dermal plate patterns, but noted that some variation may be due to factors such as ageing or even crushing. Tail clubs would appear to hold promise should they have served a purpose in either male combat or as a sexual display, but variation in this structure in regard to sexual dimorphism was repudiated by Coombs (1995).…”