Editing Ankylosaurus (section)

===Armor===
[[File:Ankylosaurus armor.png|thumb|Arrangement of armor as suggested by [[Victoria M. Arbour|Arbour]] and Mallon, 2017]] 
A prominent feature of ''Ankylosaurus'' was its armor, consisting of knobs and plates of bone known as osteoderms, or scutes, embedded in the skin. These have not been found in articulation, so their exact placement on the body is unknown, though inferences can be made based on related animals, and various configurations have been proposed. The osteoderms ranged from {{convert|1|cm|in|frac=4|sp=us}} in diameter to {{convert|35.5|cm|in|frac=4|abbr=on}} in length, and varied in shape. The osteoderms of ''Ankylosaurus'' were generally thin walled and hollowed on the underside. Compared to ''Euoplocephalus'', the osteoderms of ''Ankylosaurus'' were smoother. Many smaller osteoderms and ossicles probably occupied the space between the larger ones, as in other ankylosaurids. The osteoderms covering the body were very flat, though with a low keel at one margin. In contrast, the nodosaurid ''Edmontonia'' had high keels stretching from one margin to the other on the midline of its osteoderms. ''Ankylosaurus'' had some smaller osteoderms with a keel across the midline.<ref name="2017desc"/><ref name="carpenter2004"/> 

{{multiple image
|align = left
|total_width = 400
|image1 = Ankylosaurus cervical half rings.gif
|alt1 = Armor

|image2 = Newly identified elements the holotype of Ankylosaurus.gif
||alt2 = 

|footer = Left: Cervical half ring from the neck of ''[[Euoplocephalus]]'' (A–B) compared with half-ring fragments (C–J) of ''Ankylosaurus'' (holotype), and possible back [[osteoderm]]s (K–L). Right: elements of the holotype that were identified in 2017, including parts of the skull (A–D) and cervical half rings (E–H)
}}

Like other ankylosaurids, ''Ankylosaurus'' had {{Dinogloss|cervical half-rings}} (armor plates on the neck), but these are known only from fragments, making their exact arrangement uncertain. Carpenter suggested that when seen from above, the plates would have been paired, creating an inverted V-shape across the neck, with the midline gap probably being filled with small ossicles (round bony scutes) to allow for movement. He believed the width of this armor belt was too wide to have fitted solely on the neck, and that it covered the base of the neck and continued onto the shoulder region. Arbour and the Canadian paleontologist [[Philip J. Currie]] disagreed with Carpenter's interpretation in 2015 and pointed out that the cervical half-ring fragments of the holotype specimen did not fit together in the way proposed by Carpenter (though this could be due to breakage). They instead suggested that the fragments represented the remains of two cervical half-rings, which formed two semi-circular plates of armor around the upper part of the neck, as in the closely related ''[[Anodontosaurus]]'' and ''Euoplocephalus''.<ref name="carpenter2004"/><ref name="systematics ankylosaurid"/> Arbour and Mallon elaborated on this idea, describing the shape of these half-rings as "continuous U-shaped yokes" over the upper part of the neck, and suggested that ''Ankylosaurus'' had six keeled osteoderms with oval bases on each half-ring.<ref name="2017desc"/>

The first osteoderms behind the second cervical half-ring would have been similar in shape to those in the first half-ring, and the osteoderms on the back probably decreased in diameter hindwards. The largest osteoderms were probably arranged in transverse and longitudinal rows across most of the body, with four or five transverse rows separated by creases in the skin. The osteoderms on the flanks would probably have had a more square outline than those on the back. There may have been four longitudinal rows of osteoderms on the flanks. Unlike some basal ankylosaurs and many nodosaurs, ankylosaurids do not appear to have had co-ossified pelvic shields above their hips. Some osteoderms without keels may have been placed above the hip region of ''Ankylosaurus'', as in ''Euoplocephalus''. ''Ankylosaurus'' may have had three or four transverse rows of circular osteoderms over the pelvic region, which were smaller than those on the rest of the body, as in ''[[Scolosaurus]]''. Smaller, triangular osteoderms may have been present on the sides of the pelvis. Flattened, pointed plates resemble those on the sides of the tail of ''Saichania'', and may have been distributed similarly on ''Ankylosaurus''. Osteoderms with oval keels could have been placed on the upper side of the tail or the side of the limbs. Compressed, triangular osteoderms found with ''Ankylosaurus'' specimens may have been placed on the sides of the pelvis or the tail. Ovoid, keeled, and teardrop-shaped osteoderms are known from ''Ankylosaurus'', and may have been placed on the forelimbs, like those known from ''Pinacosaurus'', but it is unknown whether the hindlimbs bore osteoderms.<ref name="carpenter2004"/><ref name="2017desc"/> 

[[File:Ankylosaurus tail club.jpg|thumb|alt=Fossilized tail club, black in coloring|Only known [[tail club]] (AMNH 5214), [[American Museum of Natural History]]]]
The tail club (or tail knob) of ''Ankylosaurus'' was composed of two large osteoderms, with a row of small osteoderms at the midline, and two small osteoderms at the tip; these osteoderms obscured the last tail vertebra. As only the tail club of specimen AMNH 5214 is known, the range of variation between individuals is unknown. The tail club of AMNH 5214 is {{convert|60|cm|in|frac=2|abbr=on}} long, {{convert|49|cm|in|frac=2|abbr=on}} wide, and {{convert|19|cm|in|frac=2|abbr=on}} tall. The club of the largest specimen may have been {{convert|57|cm|in|frac=2|abbr=on}} wide. The tail club of ''Ankylosaurus'' was semicircular when seen from above, similar to those of ''Euoplocephalus'' and ''Scolosaurus'' but unlike the pointed club osteoderms of ''Anodontosaurus'' or the narrow, elongated club of ''Dyoplosaurus''. The last seven tail vertebrae formed the "handle" of the tail club. These vertebrae were in contact, with no cartilage between them, and were sometimes co-ossified, which made them immobile. Ossified tendons attached to the vertebrae in front of the tail club, and these features together helped strengthen it. The interlocked [[Articular processes|zygapophyses]] (articular processes) and neural spines of the handle vertebrae were U-shaped when seen from above, whereas those of most other ankylosaurids are V-shaped, which may be due to the handle of ''Ankylosaurus'' being wider. The larger width may indicate that the tail of ''Ankylosaurus'' was shorter in relation to its body length than those of other ankylosaurids, or that it had the same proportions but with a smaller club.<ref name="2017desc"/><ref name="carpenter2004"/><ref>{{Cite journal|doi=10.1111/joa.12363|pmid=26332595|title=Ankylosaurid dinosaur tail clubs evolved through stepwise acquisition of key features|journal=Journal of Anatomy|volume=227|issue=4|pages=514–23|year=2015|last1=Arbour|first1=V. M.|last2=Currie|first2=P. J.|pmc=4580109}}</ref>