Akainacephalus

Akainacephalus is a genus of herbivorous ankylosaurid dinosaur from the Campanian age Kaiparowits Formation of southern Utah. The type and only species is Akainacephalus johnsoni, known from the most complete ankylosaur specimen ever discovered from southern Laramidia, including a complete skull, tail club, a number of osteoderms, limb elements and part of its pelvis, among other remains.[1]

Akainacephalus
Temporal range: Upper Campanian, 75.97 Ma
Akainacephalus reconstructions
Preserved elements and skeletal reconstructions
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Order: Ornithischia
Family: Ankylosauridae
Tribe: Ankylosaurini
Genus: Akainacephalus
Wiersma and Irmis, 2018
Species:
A. johnsoni
Binomial name
Akainacephalus johnsoni
Wiersma and Irmis, 2018

Discovery and naming

Akainacephalus skull above and below
Skull from above and below

In 2008, in the Grand Staircase-Escalante National Monument in Kane Country, Utah, an ankylosaurian skeleton was discovered at a site first located by Scott Richardson, an employee of the Bureau of Land Management. In 2009, the excavation was completed by a team headed by R. Irmis. The skull of the skeleton was during four years prepared by volunteer Randy Johnson, a retired chemist. In January 2014, the skull was investigated by means of a CAT-scan.[1]

In 2018, the type species Akainacephalus johnsoni was named and described by Dutch paleontologist Jelle P. Wiersma and Randall Benjamin Irmis. The generic name combines a Greek ἄκαινα, akaina, "spike", a reference to the spiky head armour, with κεφαλή, kephalè, "head". The specific name honours Randy Johnson as preparator.[1]

The holotype, UMNH VP 20202, was found in a layer of the Kaiparowits Formation dating from late Campanian. The age of the layer was determined at 75.97 million years by zircon dating. The holotype consists of a partial skeleton with skull. It contains the complete skull and lower jaws, including the predentary; four back vertebrae; eight sacral vertebrae; eight "free" tail vertebrae; eleven tail vertebrae forming the handle of the tail club; the tail club itself; ribs; both shoulder blades; a left coracoid; a right humerus; a right ulna; a left ilium; a left thighbone; a left shinbone; a left calfbone; a toe phalanx; a claw; two cervical halfrings; and fourteen osteoderms of the back and flanks. It represents about 45% of the skeletal elements. It is part of the collection of the Natural History Museum of Utah in Salt Lake City.[1]

Description

Akainacephalus club
Tail handle and club

The describing authors indicated several distinguishing traits. Some of these are autapomorphies, unique derived characters. The supraorbital bosses are massive in side view, forming a high back-swept ridge, also extending sideways over the eye socket, while encompassing the front top corner and the rear edge of the eye socket. The cheek horns are triangular, pointing almost vertically to below. On the frontal bones, a central large flat hexagonal osteoderm is present. The zone spanning the frontal bones and nasal bones is covered by symmetrically positioned, closely packed, pyramid-shaped and conical caputegulae. The nasal bones exhibit a distinct central row of conical caputegulae, symmetrically separated from the osteoderms above and to the sides of them. At the rear of the skull, the part of the foramen magnum formed by the basioccipital is located obliquely above and in front of the occipital condyle.[1]

Akainacephalus and nodocephalosaurus skulls
Skull compared to that of its closest relative, Nodocephalosaurus

The head armour of Akainacephalus is strikingly similar to that of Nodocephalosaurus, a related form also found in southern Laramidia, in New Mexico. The description therefore closely compared the two genera in order to prove that Akainacephalus was a valid taxon. Akainacephalus and Nodocephalosaurus share certain traits such as pyramid-shaped osteoderms on the snout and flaring armour above the nostrils. There are, however, also differences. With Akainacephalus, the osteoderms of the front and rear supraorbitals form a single back-swept high structure. In N. kirtlandensis, these remain separate elements of far smaller size. Akainacephalus has a much smaller squamosal horn. Its cheek horn points straight to below as an enormous triangle, while that of Nodocephalosaurus curves to behind like a smaller curved fin. A comparison is complicated by the fact that the skull of Nodocephalosaurus is only partly known. Besides, with the holotype of Akainacephalus the squamosal horns have broken off, making it impossible to determine their exact shape, and the skull as a whole has been compressed from front to rear, creating a kink from which snout and rear are appending, and narrowing and raising the area around the eye socket. However, Nodocephalosaurus was found in the Kirtland Formation, in layers that are three million years younger, which precludes the taxa from being identical.[1]

Akainacephalus sacrum
Sacrum and caudosacral vertebrae

The front snout bones, the premaxillae, form a wide, U-shaped, upper beak, wider than long. The sides of the snout are not covered by armour. The number of maxillary teeth, per side, has been estimated at a minimum of sixteen. The bony nostrils are oriented to the side of the snout. The nostril is rather small and not clearly subdivided into smaller openings. The quadrate bone is strongly inclined, causing the jaw joint to be positioned, visible in side view, in front of the cheek horn point, which has not been reported in other ankylosaurids.[1]

Classification

Ankylosaurin skulls
The skull ornamentation of Akainacephalus (left) compared to its close relatives (from left to right): Nodocephalosaurus, Tarchia, and Minotaurasaurus

Akainacephalus' phylogenetic analysis reveals it to form a clade with fellow Laramidian ankylosaurid Nodocephalosaurus.[1] Additional data from cladistic analysis also shows that Akainacephalus and Nodocephalosaurus are likewise more closely related to Asian ankylosaurid genera such as Saichania and Tarchia than to North American genera such as Euoplocephalus and Ankylosaurus itself. The discovery indicates a strong case for provincialism between dinosaur populations in Northern and Southern Laramidia. Furthermore, the discovery of Akainocephalus also indicates at least two faunal migrations between Asia and North America, created when dropping sea levels allowed migrations between the continents via the Beringian Land Bridge.[1]

Paleoecology

During the Late Cretaceous period, the site of the Kaiparowits Formation was located near the western shore of the Western Interior Seaway, a large inland sea that split North America into two landmasses, Laramidia to the west and Appalachia to the east. The plateau where dinosaurs lived was an ancient floodplain dominated by large channels and abundant wetland peat swamps, ponds and lakes, and was bordered by highlands. The climate was wet and humid, and supported an abundant and diverse range of organisms.[2] This formation contains one of the best and most continuous records of Late Cretaceous terrestrial life in the world.[3]

Akainacephalus shared its paleoenvironment with other dinosaurs, such as dromaeosaurid theropods, the troodontid Talos sampsoni, tyrannosaurids like Teratophoneus, the duckbilled hadrosaurs Parasaurolophus cyrtocristatus and Gryposaurus monumentensis, the ceratopsians Utahceratops gettyi, Nasutoceratops titusi and Kosmoceratops richardsoni and the oviraptorosaurian Hagryphus giganteus. Some fossil evidence suggests the presence of the tyrannosaurid Albertosaurus and the ornithomimid Ornithomimus velox, but the existing assessment of the material is not conclusive. Paleofauna present in the Kaiparowits Formation included chondrichthyans (sharks and rays), frogs, salamanders, turtles, lizards and crocodilians. A variety of early mammals were present including multituberculates, marsupials, and insectivorans.

See also

References

  1. ^ a b c d e f g h i Jelle P. Wiersma; Randall B. Irmis (2018). "A new southern Laramidian ankylosaurid, Akainacephalus johnsoni gen. et sp. nov., from the upper Campanian Kaiparowits Formation of southern Utah, USA". PeerJ. 6: e5016. doi:10.7717/peerj.5016.
  2. ^ Titus, Alan L. and Mark A. Loewen (editors). At the Top of the Grand Staircase: The Late Cretaceous of Southern Utah. 2013. Indiana University Press. Hardbound: 634 pp.
  3. ^ Clinton, William. "Presidential Proclamation: Establishment of the Grand Staircase-Escalante National Monument". September 18, 1996. Archived from the original on 2013-08-28. Retrieved 9 November 2013.

External links

Andrey Atuchin

Andrey Atuchin is a Russian paleoartist, illustrator and biologist who focuses on artistic reconstructions of extinct animals. He is known for his clean, detailed style reminiscent of classic National Geographic illustrations. Atuchin has collaborated with paleontologists all over the world in illustrating new species for papers and press releases, such as the 2014 feathered dinosaur Kulindadromeus zabaikalicus, as well as more recent discoveries including the pliosaur Luskhan itilensis, described in 2017, and the 2018 ankylosaur dinosaur Akainacephalus johnsoni.

Ankylosaurinae

Ankylosaurinae is a subfamily of ankylosaurid dinosaurs, existing from the Early Cretaceous about 105 million years ago until the end of the Late Cretaceous, about 66 mya. Many genera are included in the clade, such as Ankylosaurus, Pinacosaurus, Euoplocephalus, and Saichania.

Bienosaurus

Bienosaurus (meaning "Bien's lizard") was a dinosaur from the Early Jurassic (probably Sinemurian). The genus was an armoured dinosaur from the Lower Lufeng Formation in Yunnan Province in China.

Dongyangopelta

Dongyangopelta is an extinct genus of nodosaurid ankylosaurian dinosaur known from the "middle" Cretaceous Chaochuan Formation (Albian or Cenomanian stage) of Dongyang, Zhejiang Province, China. Dongyangopelta was first named by Rongjun Chen, Wenjie Zheng, Yoichi Azuma, Masateru Shibata, Tianliang Lou, Qiang Jin and Xingsheng Jin in 2013 and the type species is Dongyangopelta yangyanensis. It differs from Zhejiangosaurus, the second nodosaurid from southeast China, in the characters of presacral rod, ilium, and femur. Donyangopelta is distinguishable from Zhejiangosaurus only on the basis of the morphology of its pelvic shield.

Emausaurus

Emausaurus is a genus of thyreophoran or armored dinosaur from the Early Jurassic. Its fossils have been found in Germany. The type and only species, Emausaurus ernsti, was formalized by Harmut Haubold in 1990. The generic name is composed of an acronym of Ernst Moritz Arndt University of Greifswald and Greek sauros/σαυρος (lizard). The specific name is derived from the name of geologist Werner Ernst, who found the fossil, holotype SGWG 85, in the summer of 1963 at a loampit near Grimmen, in strata dating from the Toarcian.

Hungarosaurus

Hungarosaurus tormai is a herbivorous nodosaurid ankylosaur from the Upper Cretaceous (Santonian) Csehbánya Formation of the Bakony Mountains of western Hungary. It is the most completely known ankylosaur from the Cretaceous of Europe. Ankylosaur material had been known from Europe since the 19th century, with finds having been previously made in England, Austria, western Romania, France, and northern Spain.

Invictarx

Invictarx is a genus of herbivorous nodosaurid dinosaur from New Mexico dating from the early Campanian epoch of the Late Cretaceous.

Loricatosaurus

Loricatosaurus (meaning "armored lizard") is a genus of stegosaurid dinosaur from Callovian-age (Middle Jurassic) rocks of England and France.

Mongolostegus

Mongolostegus is a genus of stegosaur from the Early Cretaceous (Aptian-Albian) of Mongolia.

Nodocephalosaurus

Nodocephalosaurus is a genus of herbivorous ankylosaurine ankylosaurid dinosaur from Upper Cretaceous (late Campanian stage) deposits of San Juan Basin, New Mexico. The holotype was recovered from the Late Campanian De-na-zin Member of the Kirtland Formation and consists of an incomplete skull. Nodocephalosaurus (Greek nodus = knob, kephale = head and sauros = lizard) is a monotypic genus, including only the type species, Nodocephalosaurus kirtlandensis. Dinosaurs like Nodocephalosaurus resembled Asian forms, and may be evidence for Asian dinosaurs migrating to North America in the Late Cretaceous.

Nodosaurinae

Nodosaurinae is a group of ankylosaurian dinosaurs named in 1919 by Othenio Abel.

Nodosaurus

Nodosaurus (meaning "knobbed lizard") is a genus of herbivorous ankylosaurian dinosaur from the Late Cretaceous, the fossils of which are found in North America.

Regnosaurus

Regnosaurus (meaning "Sussex lizard") is a genus of herbivorous stegosaurian dinosaur that lived during the Early Cretaceous Period in what is now England.

Silvisaurus

Silvisaurus, from the Latin silva "woodland" and Greek sauros "lizard", is a nodosaurid ankylosaur from the middle Cretaceous period.

Tatisaurus

Tatisaurus is a genus of ornithischian dinosaur from the Early Jurassic from the Lower Lufeng Formation in Yunnan Province in China. Little is known as the remains are fragmentary.

Texasetes

Texasetes (meaning "Texas resident") is a genus of ankylosaurian dinosaur from the late Lower Cretaceous of North America. This poorly known genus has been recovered from the Paw Paw Formation (late Albian) near Haslet, Tarrant County Texas, which has also produced the nodosaurid ankylosaur Pawpawsaurus. Texasetes is estimated to have been 2.5–3 meters (8–10 ft) in length. It was named by Coombs in 1995.

Tsagantegia

Tsagantegia (; meaning "of Tsagan-Teg"; Tumanova, 1993) is a genus of medium-sized ankylosaurid dinosaur from the Upper Cretaceous Mongolia, during the Cenomanian stage.

The holotype specimen (GI SPS N 700/17), a complete skull, was recovered from the Bayan Shireh Formation (Cenomanian-Santonian), at the Tsagan-Teg ("White Mountain") locality, Dzun-Bayan, in the southeastern Gobi Desert, Mongolia. The genus is monotypic, including only the type species, T. longicranialis.

Yingshanosaurus

Yingshanosaurus (meaning "Yingshan or Golden Hills reptile") is a genus of stegosaurian dinosaur from the Late Jurassic, around 155 million years ago. It was a herbivore that lived in what is now China. The type species is Yingshanosaurus jichuanensis.

Zhejiangosaurus

Zhejiangosaurus (meaning "Zhejiang lizard") is an extinct genus of nodosaurid dinosaur from the Upper Cretaceous (Cenomanian stage) of Zhejiang, eastern China. It was first named by a group of Chinese authors Lü Junchang, Jin Xingsheng, Sheng Yiming and Li Yihong in 2007 and the type species is Zhejiangosaurus lishuiensis ("from Lishui", where the fossil was found). It has no diagnostic features, and thus is a nomen dubium.

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