Ankylosauridae

Ankylosaurids
Temporal range: Early Cretaceous - Late Cretaceous, 122–66 Ma
Mounted skeleton of Euoplocephalus tutus, Senckenberg Museum
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Order: †Ornithischia
Clade: †Eurypoda
Suborder: †Ankylosauria
Family: †Ankylosauridae
Brown, 1908
Type species
†Ankylosaurus magniventris
Brown, 1908
Subfamilies

†Ankylosaurinae Brown, 1908

Synonyms

Syrmosauridae Maleev, 1952

An ankylosaurid is a member of the armored dinosaur family Ankylosauridae that appeared 122 million years ago (along with another family of ankylosaurs, the Nodosauridae) and became extinct 66 million years ago during the Cretaceous–Paleogene extinction event. Ankylosaurids have been found in western North America, Europe and East Asia, though good specimens are rare; most are known only from bone fragments.

Features

Dyoplosaurus tail reconstruction, showing terms used for parts of ankylosaurid tails

The heavy armour, forming a veritable shell on the backs of ankylosaurids and their clubbed tails, makes them look superficially similar to the mammalian glyptodonts (and to a lesser degree to the[1] giant meiolaniid turtles of Australia).

Their heavily armoured heads formed a toothless beak at the front (comparable to modern birds), though the sides of the mouth and the lower jaw did bear small teeth, deeply inset from the jaw. Among all the ornithischians, the endocranial anatomy of ankylosaurs is the most poorly known.[2]

Armor

Ankylosaurids usually had a thick armour plating of fused bone, often interspersed with a variety of spikes and lumps. Ankylosaurids were so heavily armored that some advanced species even had armoured eyelids.

Tail

Many ankylosaurids also had an enlarged mass of bone forming a "club" on the end of their tails, made of two enlarged bone lumps. This tail club has traditionally been used to separate ankylosaurids from their close relatives the nodosaurids, although the many primitive ankylosaurids ("shamosaurines", and even basal ankylosaurines) also lacked bony tail clubs.

Earliest ankylosaurs and nodosaurids did not have tail clubs. Tail clubs evolved in the subgroup ankylosaurids with a handle and a knob. The handle was a sequence of interlocking vertebrae at the end of the tail, the knob was a bony end. The handle evolved first per studies with two dinosaurs: Liaoningosaurus paradoxus lived 122 million years ago, Zhongyuansaurus luoyangensis lived about 92 million years ago, each had versions of the handle but no tail knobs. Ankylosaurs with tail clubs evolved around 75 million years ago. The theory is the tail evolved first to be a stiff appendage then the tail end club evolved. Ankylosaurs had osteoderms on the sides of their tails since the earliest ancestors Scelidosaurus.[3][4][5]

Relationships

Diagram showing ankylosaurid skull anatomy

The polacanthids are sometimes included as a subfamily of ankylosaurids, as Polacanthinae. However, phylogenetic analyses since 2000 have shown the polacanthids to form either a natural group apart from the ankylosaurids, or to be an unnatural grouping of primitive ankylosaurs.[6]

Ankylosauria and Stegosauria are now grouped together within the clade Thyreophora. This group first appeared in the Sinemurian age, and survived for 135 million years, until disappearing in the Maastrichtian. They were widespread and inhabited a broad range of environments.[7][8] As more complete specimens and new genera have been discovered, theories about ankylosaurian interrelatedness have become more complex, and hypotheses have often changed between studies. In addition to Ankylosauridae, Ankylosauria has been divided into the families Nodosauridae, and sometimes Polacanthidae (these families lacked tail clubs).[9] Ankylosaurus is considered part of the subfamily Ankylosaurinae (members of which are called ankylosaurines) within Ankylosauridae.[9] Ankylosaurus appears to be most closely related to Anodontosaurus and Euoplocephalus.[10] The following cladogram is based on a 2015 phylogenetic analysis of the Ankylosaurinae conducted by Arbour and Currie:[11]

Ankylosaurinae

Crichtonpelta

Tsagantegia

Zhejiangosaurus

Pinacosaurus


Saichania

Tarchia

Zaraapelta




Ankylosaurini

Dyoplosaurus


Talarurus

Nodocephalosaurus


Ankylosaurus

Anodontosaurus

Euoplocephalus

Scolosaurus

Ziapelta









Since Ankylosaurus and other Late Cretaceous North American ankylosaurids grouped with Asian genera (in a tribe the authors named Ankylosaurini), Arbour and Currie suggested that earlier North American ankylosaurids had gone extinct by the late Albian or Cenomanian ages of the Middle Cretaceous. Ankylosaurids thereafter recolonised North America from Asia during the Campanian or Turonian ages of the Late Cretaceous, and diversified there again, leading to genera such as Ankylosaurus, Anodontosaurus, and Euoplocephalus. This explains a 30 million year gap in the fossil record of North American ankylosaurids between these ages.[11]

Timeline of discoveries

Zhongyuansaurus Tsagantegia Tianzhenosaurus Tarchia Talarurus Shanxia Scolosaurus Saichania Pinacosaurus Oohkotokia Nodocephalosaurus Minotaurasaurus Euoplocephalus Dyoplosaurus Crichtonsaurus Anodontosaurus Ankylosaurus Ahshislepelta Shamosaurus Minmi (dinosaur) Liaoningosaurus Gobisaurus Cedarpelta Aletopelta

Timeline of genera

Cretaceous Jurassic Late Cretaceous Early Cretaceous Late Jurassic Middle Jurassic Early Jurassic Ankylosaurus Tarchia Saichania Anodontosaurus Oohkotokia Shanxia Aletopelta Ahshislepelta Nodocephalosaurus Euoplocephalus Dyoplosaurus Scolosaurus Pinacosaurus Minotaurasaurus Gobisaurus Tsagantegia Talarurus Crichtonsaurus Zhongyuansaurus Cedarpelta Shamosaurus Minmi (dinosaur) Liaoningosaurus Cretaceous Jurassic Late Cretaceous Early Cretaceous Late Jurassic Middle Jurassic Early Jurassic

See also

References

  1. ↑ Switek, Brian. "Join the Club - How Ankylosaurs Evolved Their Formidable Tails". Retrieved 2015-09-05.
  2. ↑ Coombs W. (1978). "An endocranial cast of Euoplocephalus (Reptilia, Ornithischia)". Palaeontographia, Abteilung A 161: 176–82.
  3. ↑ "Pseudoplocephalus: How the ankylosaur got its tail club". Pseudoplocephalus. 2015-08-31. Retrieved 2015-09-05.
  4. ↑ Arbour, Victoria M.; Currie, Philip J. (2015-08-01). "Ankylosaurid dinosaur tail clubs evolved through stepwise acquisition of key features". Journal of Anatomy 227: n/a–n/a. doi:10.1111/joa.12363. ISSN 1469-7580. PMID 26332595.
  5. ↑ Switek, Brian. "Join the Club - How Ankylosaurs Evolved Their Formidable Tails". Retrieved 2015-09-05.
  6. ↑ Hayashi, S.; Carpenter, K.; Scheyer, T.M.; Watabe, M.; Suzuki, D. (2010). "Function and evolution of ankylosaur dermal armor". Acta Palaeontologica Polonica 55 (2): 213–228. doi:10.4202/app.2009.0103.
  7. ↑ Carpenter, K. (2004). "Redescription of Ankylosaurus magniventris Brown 1908 (Ankylosauridae) from the Upper Cretaceous of the Western Interior of North America". Canadian Journal of Earth Sciences 41: 961–86. doi:10.1139/e04-043.
  8. ↑ Coombs, W. (1978). "The families of the ornithischian dinosaur order Ankylosauria" (PDF). Journal of Paleontology 21 (1): 143–170.
  9. 1 2 Thompson, R. S.; Parish, J. C.; Maidment, S. C. R.; Barrett, P. M. (2012). "Phylogeny of the ankylosaurian dinosaurs (Ornithischia: Thyreophora)". Journal of Systematic Palaeontology 10 (2): 301–312. doi:10.1080/14772019.2011.569091.
  10. ↑ Arbour, V.M.; Currie, P.J.; Badamgarav, D. (2014). "The ankylosaurid dinosaurs of the Upper Cretaceous Baruungoyot and Nemegt formations of Mongolia". Zoological Journal of the Linnean Society 172: 631–652. doi:10.1111/zoj.12185.
  11. 1 2 Arbour, V. M.; Currie, P. J. (2015). "Systematics, phylogeny and palaeobiogeography of the ankylosaurid dinosaurs". Journal of Systematic Palaeontology: 1–60. doi:10.1080/14772019.2015.1059985.

External links

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