Figure 1.
Diagram of tail terminology used in this paper.
Ankylosaurid tail reconstructed from ROM 784; ROM 784 lacks the transitional caudal vertebra and the anterior portion of the pelvis. Scale bar equals 1 m. Modified from Arbour et al. (in press).
Figure 2.
Morphology of ankylosaurid tail clubs.
A) UALVP 47273, dorsal view. B) ROM 784 dorsal view and C) posterior view, D) UALVP 16247 dorsal view, E) AMNH 5245 dorsal view, and F) ROM 788 ventral view.
Figure 3.
CT scan images of transverse slices through UALVP 47273 handle vertebrae in anterior view, dorsal is up.
A) Midlength of a vertebra, with B) position in specimen, oblique view, anterior is to the left. C) Posterior to midlength of vertebra, with D) position in specimen. Scale bar in A and C equals 5 cm. Three-dimensional reconstructions in B and D created in Mimics. Abbreviations are as follows: c, centrum; ha, haemal arch; hc, haemal canal; na, neural arch of the centrum in the slice; na1, neural spine of the anterior vertebra; na2, prezygapophyses of the posterior vertebra; nc, neural canal; o, ossified tendon.
Figure 4.
CT scan images of sagittal slices through UALVP 47273 handle in left lateral view, dorsal is up.
A) Mid-width of the club. Most of the centra appear to be fused at the anterior and proximal faces (arrow with open head), although one joint does not appear fused (arrow with closed head), with B) position in specimen, oblique dorsal view, anterior is to the right. C) Mid-width of the left half of the club, with D) position in specimen. The neural canal extends to the anterior terminus of the minor plates at the distal end of the knob (arrow). The three narrow, vertically stacked structures at the anterior of the handle are ossified tendons. Scale bar equals 10 cm. Three-dimensional reconstructions in B and D created in Mimics.
Figure 5.
Internal anatomy of a tail club knob.
A) CT scan image of coronal slices through UALVP 16247 in dorsal view, at knob mid-height, posterior is up. B) Interpretive illustration of (A), showing the shapes of the vertebrae, highest density areas (white), medium density areas (light grey), and lowest density areas (dark grey). The neural canal and vascular canals in the osteoderms are indicated by black. Scale bar equals 5 cm.
Figure 6.
CT scan images of transverse slices through knobs, dorsal is up.
A) UALVP 47273, with B) position in specimen. The arrowhead marks three vertically stacked ossified tendons between the left major osteoderm and the vertebra. C) UALVP 47273, with D) position in specimen. E) UALVP 16247, with F) position in specimen. G) ROM 788, with H) position in specimen; artifacts obscure most fine details. The arrowhead marks the CT scanning tray. Scale bars in A, C, and E equal 5 cm, scale bar in G equals 10 cm. Three-dimensional reconstructions in B, D, F, and G created in Mimics (not to scale).
Figure 7.
Ossified tendons in ROM 784, oblique right lateral view.
M. spinalis is represented by the inner set of imbricated tendons, and M. longissimus caudae is represented by the outer set of parallel to braided tendons. The ossified tendons continue underneath the knob osteoderms (arrowhead). Scale bar equals 10 cm.
Figure 8.
Origins of tail muscles on the pelvis.
A) AMNH 5409 (Euoplocephalus) pelvis, posterior right dorsolateral view. M. ischiocaudalis originates at the distal terminus of the ischium. The origin of M. longissimus caudae is marked by a long, pronounced ridge and rugose area on the lateral aspect of the ilium. The posterior terminus of the ilium is partially reconstructed. B) AMNH 5337 (Euoplocephalus) pelvis, dorsal view, anterior up, showing the posterior terminus of the left ilium. M. iliocaudalis originates from a large knob. C) AMNH 5409, same view as (A), with reconstructed musculature. The muscles are cut posteriorly to show their relationships in cross-section. M. caudofemoralis longus originates on the transverse processes of the free caudal vertebrae, and inserts on the fourth trochanter of the femur (not shown). M. transversospinalis originates and inserts on the neural spines. Scale bars equal 10 cm. Abbreviations are as follows: ca = M. caudofemoralis longus, il = M. iliocaudalis, is = M. ischiocaudalis, lo = M. longissimus caudae, tr = M. transversospinalis.
Figure 9.
Cross-sectional reconstructions of ankylosaurid caudal musculature.
A) Anterior free caudal vertebra, modified from TMP 85.26.70 (Euoplocephalus). M. transversospinalis is not divided into its subunits. The relative sizes of all muscles are speculative, especially M. iliocaudalis and M. ischiocaudalis. B) More muscular reconstruction, with muscles bulging past neural spine, haemal spine, and transverse processes. This reconstruction is 43% larger than the reconstruction in A. C) Posterior free caudal vertebra, reconstructed from TMP 2007.20.100. M. iliocaudalis may not have extended very far posteriorly along the tail, in which case M. ischiocaudalis may have occupied the area reconstructed as M. ischiocaudalis here. D) Musculature of the handle, reconstructed from a CT scan image of UALVP 47273 at the midlength of the club. M. transversospinalis and M. longissimus caudae are represented by ossified tendons in many tail club specimens. The size of M. iliocaudalis is speculative. The width of M. longissimus caudae is equivalent to the maximum space between the major osteoderms of the knob. Scale equals 5 cm.
Table 1.
Summary of volumes, areas, and masses for the ROM 784/UALVP 47273 composite tail. Muscle and bone mass are after Carpenter et al. (2005).
Table 2.
Rotational inertias for each segment of the ROM 784/UALVP 47273 composite tail.
Table 3.
Muscle cross-sectional areas, muscle forces, and torques for each segment of the ROM 784/UALVP 47273 composite tail.
Table 4.
Cumulative moment of inertias and segment angular rate of movement.
Table 5.
Summary of results of sensitivity analyses for ROM 784/UALVP 47273– angular accelerations, velocities, and impulses.
Table 6.
Summary of results of sensitivity analyses for ROM 784/UALVP 47273– forces and stresses.
Table 7.
Percentage difference between the baseline analyses and each sensitivity analysis for angular acceleration, impact velocity, impulse, impact force, and impact stress.
Table 8.
Impact velocities, impulses, forces, and stresses for the AMNH 5245/ROM 788 composite tail.
Table 9.
Impact velocities, impulses, forces, and stresses for the UALVP 16247 reconstructed tail.
Figure 10.
Diagram showing the approximate right lateroflexion of the tail in Euoplocephalus, and the definition of the half angle of articulation θ.
Figure 11.
Diagrammatic representation of composite tails used in this study.
A) ROM 784 (Dyoplosaurus)/UALVP 47273 (Euoplocephalus) composite tail. ROM 784 elements indicated by light grey. UALVP 47273 elements indicated by dark grey. The black vertebra represents the transitional vertebra in ROM 1930. Its presence is inferred by the gap at this location in ROM 784. The light purple area represents the free caudal tail frustum, and the dark purple area represents a single free caudal tail segment. The orange area represents the transitional tail frustum, and the pink area represents the handle volume. B) UALVP 16247 reconstructed tail. Only the knob is preserved (dark grey); the rest of the tail is reconstructed from measurements of ROM 784 (black). C) AMNH 5245/ROM 788 composite tail. AMNH 5245 elements are light grey, ROM 788 elements are dark grey, and elements reconstructed from ROM 784 are black.
Table 10.
Actual and ideal values for dimensions of the centra in ROM 784, in mm.
Table 11.
Actual and ideal values for dimensions of the tail in ROM 784, in mm.
Figure 12.
Graph comparing the length of the neural spine of the handle vertebrae in ROM 784 and UALVP 47273.
ROM 784 is represented by the solid line and squares. UALVP 47273 is represented by the dashed line and diamonds. Source data are in Table 12.
Table 12.
Comparison of handle vertebra neural spine length, and knob width (in mm), in ROM 784 and UALVP 47273.
Figure 13.
Determining the maximum angle of rotation in ankylosaurid free caudal vertebrae.
A dorsal view of TMP 2007.20.80 is on the left, and a 3% larger copy is on the right. The vertebrae are separated by a 2 cm gap representing the intervertebral cartilage. The left vertebra is rotated from 0 to 25 degrees, in 5 degree increments, from A to F. The articular faces of the prezygapophyses in light grey, and the area covered by the postzygapophyses in darker grey, are shown for each rotation. Scale bar equals 5 cm.
Table 13.
Area of overlap between successive zygapophyses, in mm.
Table 14.
Cross-sectional area of UALVP 16247 handle and comparisons with ROM 788 and UALVP 47273.