page_title: Ankylosaurus
section_title: Armor
hierarchical_section_title: Ankylosaurus / Description / Armor
caption_attribution_description: Portions of Ankylosaurus (AMNH 5895) cervical half rings compared with the first cervical half ring of Euoplocephalus (AMNH 5406), and Ankylosaurus (AMNH 5895) postcervical osteoderms. (A) Complete (but distorted) first cervical half ring of Euoplocephalus (AMNH 5406) in&#160;?anterior view, showing arrangement of osteoderms on the underlying band of bone, and (B) interpretive illustration. The medial and lateral osteoderm pairs sit atop flat band segments, but the distal osteoderms slightly envelop the tip of their band segments. (C) Portion of Ankylosaurus first cervical half ring with lateral and distal osteoderms in external view, and (D) interpretive illustration. (E) Portion of same half ring in internal view, and (F) interpretive illustration. Carpenter (2004) suggested that a second fragment of cervical half ring bearing a single osteoderm was a continuation of the segment figured here in C–F. In G–J, the cervical half ring fragment illustrated in C–F is located to the left, and the second fragment is located on the right. (G) These pieces (here in oblique anterior or posterior internal view) cannot be reunited along their broken edges and probably do not represent the same half ring; (H) interpretive illustration. (I) The osteoderm morphology of the fragment of cervical half ring with only a single preserved osteoderm (here in oblique anterior or posterior external view) is similar to that of the distal osteoderm of the more complete specimen, but is substantially larger, and thus probably represents a distal osteoderm from the second cervical half ring, which is typically larger in specimens of Euoplocephalus (Arbour and Currie 2013a); (J) interpretive illustration. (K) and (L) large postcervical osteoderms from Ankylosaurus (AMNH 5895), probably derived from medial positions along the back; the osteoderm in (L) is similar in shape to those immediately posterior to the medial cervical half ring osteoderms in Saichania (MPC 100/151) (Arbour and Currie 2013a, 2013b). b, cervical half ring band; dos-1, distal osteoderm of the first cervical half ring; dos-2, distal osteoderm of the second cervical half ring; los-1, lateral osteoderm of the first cervical half ring; mos-1, medial osteoderm of the first cervical half ring; p, plaster.
context_page_description: Ankylosaurus is a genus of armored dinosaur. Its fossils have been found in geological formations dating to the very end of the Cretaceous Period, about 68–66 million years ago, in western North America, making it among the last of the non-avian dinosaurs. It was named by Barnum Brown in 1908; the only species in the genus is A. magniventris. The genus name means "fused lizard", and the specific name means "great belly". A handful of specimens have been excavated to date, but a complete skeleton has not been discovered. Though other members of Ankylosauria are represented by more extensive fossil material, Ankylosaurus is often considered the archetypal member of its group, despite having some unusual features.
  Possibly the largest-known ankylosaurid, Ankylosaurus is estimated to have been between 6 and 8 metres long and to have weighed between 4.8 and 8 tonnes. It was quadrupedal, with a broad, robust body. It had a wide, low skull, with two horns pointing backward from the back of the head, and two horns below these that pointed backward and down. Unlike other ankylosaurs, its nostrils faced sideways rather than towards the front.
context_section_description: 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 1 cm (0.4 in) in diameter to 35.5 cm (14.0 in) 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. 
  Like other ankylosaurids, Ankylosaurus had 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 specimen AMNH 5895 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. 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.
  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. 
  The tail club (or tail knob) of Ankylosaurus was composed of two large osteoderms, with a row of small osteoderms at th
caption: Cervical half ring from the neck of Euoplocephalus (A–B) compared with half-ring fragments (C–J) of Ankylosaurus (AMNH 5895), and possible back osteoderms (K–L)