Ankylosauria

Ankylosauria

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Ankylosauria is a group of herbivorous dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...

s of the order Ornithischia
Ornithischia
Ornithischia or Predentata is an extinct order of beaked, herbivorous dinosaurs. The name ornithischia is derived from the Greek ornitheos meaning 'of a bird' and ischion meaning 'hip joint'...

. It includes the great majority of dinosaurs with armor
Armour (zoology)
Armour in animals is external or superficial protection against attack by predators, formed as part of the body , usually through the hardening of body tissues, outgrowths or secretions. It has therefore mostly developed in 'prey' species...

 in the form of bony osteoderms. Ankylosaurs were bulky quadruped
Quadruped
Quadrupedalism is a form of land animal locomotion using four limbs or legs. An animal or machine that usually moves in a quadrupedal manner is known as a quadruped, meaning "four feet"...

s, with short, powerful limbs. They are first known to have appeared in the early Jurassic Period of China
People's Republic of China
China , officially the People's Republic of China , is the most populous country in the world, with over 1.3 billion citizens. Located in East Asia, the country covers approximately 9.6 million square kilometres...

, and persisted until the end of the Cretaceous Period. They have been found on every continent except Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...

. The first dinosaur ever discovered in Antarctica was the ankylosaurian Antarctopelta
Antarctopelta
Antarctopelta was a genus of ankylosaurian dinosaur with one known species, A. oliveroi, which lived in Antarctica during the Late Cretaceous Period. It was a medium-sized ankylosaur, reaching no more than 4 meters in length, and showed characteristics of two different families, making more...

, fossils of which were recovered from Ross Island
Ross Island
Ross Island is an island formed by four volcanoes in the Ross Sea near the continent of Antarctica, off the coast of Victoria Land in McMurdo Sound.-Geography:...

 in 1986.

Ankylosauria was first described by Henry Fairfield Osborn
Henry Fairfield Osborn
Henry Fairfield Osborn, Sr. ForMemRS was an American geologist, paleontologist, and eugenicist.-Early life and career:...

 in 1923. In the Linnaean classification system, the group is usually considered a suborder or an infraorder. It is contained within the group Thyreophora
Thyreophora
The Thyreophora were a subgroup of the ornithischian dinosaurs...

, which also includes the stegosaurs, armored dinosaurs known for their combination of plates and spikes.

Classification


Ankylosauria is split into two or three families
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

: Nodosauridae
Nodosauridae
Nodosauridae is a family of ankylosaurian dinosaurs, from the Late Jurassic to the Late Cretaceous Period of what are now North America, Asia, Antarctica and Europe.-Characteristics:...

 (the nodosaurids), Ankylosauridae
Ankylosauridae
An ankylosaurid is a member of the Ankylosauridae family of armored dinosaurs that evolved 125 million years ago and became extinct 65 million years ago during the Cretaceous-Tertiary extinction event...

 (the ankylosaurids), and Polacanthidae
Polacanthidae
Polacanthidae is a group of ankylosaurs. Polacanthids are late Jurassic to early Cretaceous in age, and Kirkland observed they appeared to become extinct about the same time a land bridge opened between Asia and North America....

, which may alternately be a subfamily of ankylosaurids or an unnatural grouping of species more primitive than both ankylosaurids and nodosaurids. One major difference distinguishing the ankylosaurids from the other two groups is that they have bony clubs
Club (zoology)
In zoology, a club is a bony mass at the end of the tail of some dinosaurs and of some mammals, most notably the ankylosaurids and the glyptodonts...

 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
Nodosaurus
Nodosaurus was a genus of herbivorous ankylosaurian dinosaur from the Late Cretaceous, the fossils of which are found in North America. Two incomplete specimens have been discovered in Wyoming and Kansas, and no skulls...

, Edmontonia
Edmontonia
Edmontonia was an armoured dinosaur, a part of the nodosaur family from the Late Cretaceous Period. It is named after the Edmonton Formation , the unit of rock it was found in.-Description:...

, and Sauropelta
Sauropelta
Sauropelta is a genus of nodosaurid dinosaur that existed in the Early Cretaceous Period of North America. One species has been named although others may have existed. Anatomically, Sauropelta is one of the most well-understood nodosaurids, with fossilized remains recovered in the U.S. states of...

.

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. The polacanthines include, among others, Hylaeosaurus
Hylaeosaurus
Hylaeosaurus is the most obscure of the three animals used by Sir Richard Owen to first define the new group Dinosauria, in 1842. The original specimen, recovered by Gideon Mantell from the Tilgate Forest in the south of England in 1832, now resides in the Natural History Museum of London, where...

, Polacanthus
Polacanthus
Polacanthus, deriving its name from the Ancient Greek poly-/πολυ- "many" and acantha/ακανθα "thorn" or "prickle", was an early armored, spiked, plant-eating ankylosaur from the early Cretaceous period. Early depictions often gave it a very vague head as it was only known from the rear half of the...

and Mymoorapelta
Mymoorapelta
Mymoorapelta is an ankylosaur from the Late Jurassic Morrison Formation of western Colorado. The taxon is known from portions of a disarticulated skull, parts of three different skeletons and other postcranial remains...

. Opinions range from them belonging to their own family, the Polacanthidae, 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
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...

. 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
Ankylosaurus
Ankylosaurus is a genus of ankylosaurid dinosaur, containing one species, A. magniventris...

, Euoplocephalus
Euoplocephalus
Euoplocephalus was one of the largest genera of ankylosaurian dinosaurs, at about the size of a small elephant. It is also the ankylosaurian with the best fossil record, so its extensive spiked armor, low-slung body and great club-like tail are well documented.-Description:Among the...

, and Pinacosaurus
Pinacosaurus
Pinacosaurus is a genus of medium-sized ankylosaur dinosaurs that lived from the late Santonian to the late Campanian stages of the late Cretaceous Period , in Mongolia and China...

.

In 1997, Carpenter
Kenneth Carpenter
Kenneth Carpenter is a paleontologist. He is the museum director of the USU Eastern Prehistoric Museum and author or co-author of a number of books on dinosaurs and Mesozoic life...

 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
Scelidosaurus
Scelidosaurus is a genus of quadrupedal, lightly plated, herbivorous dinosaur about long. It lived during the Early Jurassic Period, during the Hettangian to Sinemurian stages around 199.6 to 194 million years ago. Its fossils have been found in both England and in Arizona, in the United...

, which is slightly closer to ankylosaurids than to stegosaurids, is technically a member of Ankylosauria. Upon the discovery of Bienosaurus
Bienosaurus
Bienosaurus was a dinosaur from the Early Jurassic. The genus was an armoured dinosaur from the Lower Lufeng Formation in Yunnan Province in China.-Discovery and species:...

, Dong Zhiming
Dong Zhiming
Dong Zhiming , from the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing, is one of China's leading paleontologists. He began working at the IVPP in 1962, learning from Yang Zhongjian who was director at the time...

 (2001) erected the family Scelidosauridae for both of these primitive ankylosaurs.

Taxonomy


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:
  • Order Ornithischia
    Ornithischia
    Ornithischia or Predentata is an extinct order of beaked, herbivorous dinosaurs. The name ornithischia is derived from the Greek ornitheos meaning 'of a bird' and ischion meaning 'hip joint'...

     (the "bird hipped" dinosaurs)
    • Clade Thyreophora
      Thyreophora
      The Thyreophora were a subgroup of the ornithischian dinosaurs...

       (armored herbivore
      Herbivore
      Herbivores are organisms that are anatomically and physiologically adapted to eat plant-based foods. Herbivory is a form of consumption in which an organism principally eats autotrophs such as plants, algae and photosynthesizing bacteria. More generally, organisms that feed on autotrophs in...

      s)
      • Suborder Ankylosauria
        • Family Ankylosauridae
          Ankylosauridae
          An ankylosaurid is a member of the Ankylosauridae family of armored dinosaurs that evolved 125 million years ago and became extinct 65 million years ago during the Cretaceous-Tertiary extinction event...

        • Family Nodosauridae
          Nodosauridae
          Nodosauridae is a family of ankylosaurian dinosaurs, from the Late Jurassic to the Late Cretaceous Period of what are now North America, Asia, Antarctica and Europe.-Characteristics:...

        • ?Family Polacanthidae
          Polacanthidae
          Polacanthidae is a group of ankylosaurs. Polacanthids are late Jurassic to early Cretaceous in age, and Kirkland observed they appeared to become extinct about the same time a land bridge opened between Asia and North America....

           (probably nodosaurids)

Reproduction


Possible neonate sized ankylosaur fossils have been documented in the scientific literature
Scientific literature
Scientific literature comprises scientific publications that report original empirical and theoretical work in the natural and social sciences, and within a scientific field is often abbreviated as the literature. Academic publishing is the process of placing the results of one's research into the...

.

Oilsands ankylosaurian


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
Alberta
Alberta is a province of Canada. It had an estimated population of 3.7 million in 2010 making it the most populous of Canada's three prairie provinces...

, Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...

. It would be the oldest known dinosaur specimen from the province.

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