Euoplocephalus tutus (Ankylosaur)
Project
This model was one of four ankylosaur tail clubs modeled for an MSc thesis at the University of Alberta. It has long been assumed that ankylosaurids used their tails as weapons for defense against attacks from large meat-eating theropods like Albertosaurus, Tyrannosaurus, and Tarbosaurus. Impact forces for a variety of tail club sizes were estimated and used to examine how the tail club would react during impacts. If the stresses in the models after the simulations were run exceeded that which were required to fracture bone, then it would be unlikely that ankylosaurs used their tails in a defensive manner.
The results of this study suggested that small and medium-sized tail clubs could probably withstand forceful impacts, but that the largest tail clubs may have been at risk of breaking. This in turn suggested that either 1) some ankylosaurs did not engage in the hypothesized tail-swinging behaviour, or 2) some ankylosaurs did engage in this behaviour, but did not impact with the estimated forces. It is also possible that soft tissues like intervertebral cartilages and ligaments, which were not modeled here, were important for stabilizing the tail and absorbing stress during impacts.
Arbour VM. 2009. Estimating impact forces of tail club strikes by ankylosaurid dinosaurs. PLoS ONE e6738.
Arbour VM, Snively E. 2009. Finite element analyses of ankylosaurid dinosaur tail club impacts. The Anatomical Record 292:1412-1426.
Organism
Ankylosaurid dinosaurs were quadrupedal, herbivorous dinosaurs that were covered in bony plates called osteoderms. These dinosaurs are notable for their unusual tails, which resembled clubs or axes. The tail club is composed of interlocking caudal vertebrae (the handle) and large terminal osteoderms (the knob). Ossified tendons are present alongside the handle. Tail club knobs come in a variety of shapes and sizes, but it is as yet unclear if these differences are related to ontogeny, intraspecific variation, or taxonomic variation. Euoplocephalus tutus is known from the Dinosaur Park and Horseshoe Canyon Formations of Alberta and the Two Medicine Formation of Montana, which represent rocks of late Campanian to early Maastrichtian age (76 - 70 million years ago). The tail clubs modeled in Arbour and Snively (2009) include UALVP 16247 and 47273 (located at the University of Alberta in Edmonton, Alberta), ROM 788 (located at the Royal Ontario Museum in Toronto, Ontario), and TMP 1983.36.120 (located at the Royal Tyrrell Museum of Paleontology in Drumheller, Alberta).
Model Description
This model is composed of 104,248 eight noded quadrahedral brick elements. This analysis uses material properties and forces described in Arbour and Snively (2009) under Analysis 1. The entire model is given an estimate of the material properties of cancellous bone, as the exact material properties are not known for any dinosaur bone: Young's modulus 8e9 MPa, Poisson's ratio 0.4. A force of 570 N is applied to a small area on the lateral edge of the left major osteoderm of the knob. The model is constrained at the anterior face of the handle vertebrae.
