Ankylosauria

Ankylosaurs
Temporal range: Middle JurassicLate Cretaceous, Bajocian–Maastrichtian
Euoplocephalus-tutus-1.jpg
Mounted skeleton of Scolosaurus thronus, Senckenberg Museum
Gargoyleosaurus.png
Mounted skeleton of Gargoyleosaurus, Denver Museum of Nature and Science
Scientific classification edit
Kingdom:Animalia
Phylum:Chordata
Clade:Dinosauria
Order:Ornithischia
Clade:Eurypoda
Suborder:Ankylosauria
Osborn, 1923
Subgroups

Ankylosauria is a group of mainly herbivorous dinosaurs of the order Ornithischia. It includes the great majority of dinosaurs with armor in the form of bony osteoderms. Ankylosaurs were bulky quadrupeds, with short, powerful limbs. They are known to have first appeared in the early Jurassic Period, and persisted until the end of the Cretaceous Period. They have been found on every continent. The first dinosaur ever discovered in Antarctica was the ankylosaurian Antarctopelta, fossils of which were recovered from Ross Island in 1986.

Ankylosauria was first named by Henry Fairfield Osborn in 1923.[1] In the Linnaean classification system, the group is usually considered either a suborder or an infraorder. It is contained within the group Thyreophora, which also includes the stegosaurs, armored dinosaurs known for their combination of plates and spikes.

Paleobiology

They sported a very small brain size in proportion to their body, second only to the Saurischian sauropods. They were also rather slow moving, largely because of the shortness of the limbs combined with being incapable of running. Their top speed was likely less than 10 km/hour.

Armor

Armour of Edmontonia

All ankylosaurians had armor over much of their bodies, mostly scutes and nodules, with large spines in some cases. The scutes, or plates, are rectangular to oval objects organized in transverse (side to side) rows, often with keels on the upper surface. Smaller nodules and plates filled in the open spaces between large plates. In all three groups, the first two rows of plates tend to form a sort of half-ring around the neck; in nodosaurids, this comes from adjacent plates fusing with each other (and there is a third row as well), while ankylosaurids usually have the plates fused to the top of another band of bone. The skull has armor plastered on to it, including a distinctive piece on the outside-rear of the lower jaw.

Diet and feeding

Ankylosaurs were built low to the ground, typically one foot off the ground surface. They had small, triangular teeth that were loosely packed, similar to stegosaurs. The large hyoid bones left in skeletons indicates that they had long, flexible tongues. They also had a large, side secondary palate. This means that they could breathe while chewing, unlike crocodiles. Their expanded gut region suggests the use of fermentation to digest their food, using symbiotic bacteria and gut flora. Their diet likely consisted of ferns, cycads, and angiosperms. Mallon et al. (2013) examined herbivore coexistence on the island continent of Laramidia during the Late Cretaceous. It was concluded that ankylosaurs were generally restricted to feeding on vegetation at, or below, the height of 1 meter.[2]

Reproduction

Possible neonate sized ankylosaur fossils have been documented in the scientific literature.[3]

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