| Ankylosaurs Temporal range: 200–65.5 Ma Early Jurassic - Late Cretaceous |
|
|---|---|
| Life restoration of nodosaurid Edmontonia rugosidens | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Superorder: | Dinosauria |
| Order: | †Ornithischia |
| Node: | †Eurypoda |
| Suborder: | †Ankylosauria Osborn, 1923 |
| Subgroups | |
Ankylosauria is a group of 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 first known to have appeared in the early Jurassic Period of China, and persisted until the end of the Cretaceous Period. They have been found on every continent except Africa. The first dinosaur ever discovered in Antarctica was the ankylosaurian Antarctopelta, fossils of which were recovered from Ross Island in 1986.
Ankylosauria was first described by Henry Fairfield Osborn in 1923.[1] In the Linnaean classification system, the group is usually considered 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.
Contents |
Ankylosauria is split into two or three families: Nodosauridae (the nodosaurids), Ankylosauridae (the ankylosaurids), and Polacanthidae, which may alternately be a subfamily of ankylosaurids or an unnatural grouping of species more primitive than both ankylosaurids and nodosaurids.[2] One major difference distinguishing the ankylosaurids from the other two groups is that they have bony clubs at the end of their tails, which nodosaurids and polacanthids lack.
The nodosaurids had narrow heads, and frequently had large spikes protruding from their bodies. This group traditionally includes Nodosaurus, Edmontonia, and Sauropelta.
The polacanthids were once placed in the Nodosauridae, due to their lack of tail clubs. More recently, it has been found that they probably represent a distinct group.[2] The polacanthines include, among others, Hylaeosaurus, Polacanthus and Mymoorapelta. Opinions range from them belonging to their own family, the Polacanthidae,[3] distinct from the other two or being a subfamily of the Ankylosauridae, to some researchers questioning their status as a discrete group.
The traditional ankylosaurids are from later in the Cretaceous. They had much wider bodies and have even been discovered with bony eyelids. The large clubs at the end of their tails may have been used in self-defense (swung at predators) or in sexual selection. This family included Ankylosaurus, Euoplocephalus, and Pinacosaurus.
In 1997, Carpenter defined the clade Ankylosauria as all thyreophorans closer to Ankylosaurus than to Stegosaurus (a definition followed by most paleontologists today, including Sereno, 2005). This "stem-based" definition means that the primitive armored dinosaur Scelidosaurus, which is slightly closer to ankylosaurids than to stegosaurids, is technically a member of Ankylosauria. Upon the discovery of Bienosaurus, Dong Zhiming (2001) erected the family Scelidosauridae for both of these primitive ankylosaurs.
While ranked taxonomy has largely fallen out of favor among dinosaur paleontologists, a few 21st century publications have retained the use of ranks, though sources have differed on what its rank should be. Most have listed Thyreophora as an unranked taxon containing the traditional suborders Stegosauria and Ankylosauria, though Thyreophora is also sometimes classified as a suborder, with Ankylosauria and Stegosauria as infraorders. A simplified version of one possible classification follows:
Possible neonate sized ankylosaur fossils have been documented in the scientific literature.[4]
A complete ankylosaurian skeleton was discovered by accident March 21, 2011 in approximately 110 million-year-old oil sands being excavated by Suncor near Fort McMurray, Alberta, Canada. It would be the oldest known dinosaur specimen from the province.[5]