Parankylosauria

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Parankylosaurs
Temporal range: Cretaceous, 105–70  Ma
Stegouros elengassen holotype and skeletal.png
Fossil material of Stegouros , a parankylosaur
Scientific classification Red Pencil Icon.png
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Order: Ornithischia
Clade: Thyreophora
Suborder: Ankylosauria
Clade: Parankylosauria
Soto-Acuña et al., 2021
Subgroups

Parankylosauria is a group of basal ankylosaurian dinosaurs known from the Cretaceous of South America, Antarctica, and Australia. It is thought the group split from other ankylosaurs during the mid-Jurassic period, despite this being unpreserved in the fossil record. [1]

Contents

History of research

Fossils remains of parankylosaur Antarctopelta Antarcopelta recovering.jpg
Fossils remains of parankylosaur Antarctopelta

During the Mesozoic era, the southern continents (South America, Antarctica, Australia, and Africa in addition to India and Zealandia) were unified into a supercontinent known as Gondwana. This was in contrast to the supercontinent of Laurasia in the Northern Hemisphere, with both originating from the breakup of Pangaea. Gondwana itself gradually split apart over the course of the Jurassic and Cretaceous eras. [2] Ankylosaurian dinosaurs from Laurasia have historically been far more extensively recorded and studied. Reports of the group in Gondwana date back to 1904, with a specimen from Australia and include referrals of Loricosaurus , Lametasaurus , and Brachypodosaurus to group among assorted fragmentary material. [3] Much of this material including would later be shown to be misidentified and not belonging to ankylosaurs, including the named genera. [3] [4] [5] The first definitive ankylosaur to be recognized from Gondwana was discovered in Australia in 1964 and later named in 1980 as Minmi paravertebra . [3] The possibility of a biogeographic connection between South America and ankylosaurs in Australia was raised alongside discovery, though based on conjecture. [6]

Ankylosaurs from Gondwana have remained very mysterious. Fossil material continues to be scant and southern taxa have been difficult to interpret in a phylogenetic context. Vertebrae of Antarctopelta from Antarctica, for example, were so foreign compared to those of euankylosaurs that it was questioned if they might instead belong to a marine reptile, which would make the genus based on a chimeric specimen. The discovery of the genus Stegouros, published and named in 2021, helped to clear up the previous confusion. The type specimen of the genus preserved enough of the skeleton to make it clear that there was a previously unrecognized monophyletic grouping of these southern ankylosaur taxa. Thus the study naming the genus, by Sergio Soto-Acuña and colleagues, coined Parankylosauria based on the two aforementioned genera and Kunbarrasaurus . The name, referencing its parent group, means "at the side of Ankylosauria". [1]

The Parankylosauria were not the only Gondwanan ankylosaurians; the nodosaurid Patagopelta was described from Argentina in 2022, and has been found to be closely allied with North American nodosaurids in the subfamily Nodosaurinae. This suggests that in addition to the more ancient Parankylosauria, more derived euankylosaurians also inhabited South America, having migrated from North America as part of a biotic interchange during the Campanian. [7]

Anatomy

A life reconstruction of Kunbarrasaurus, reconstructed without a macuahuitl Minmi model Canberra email.jpg
A life reconstruction of Kunbarrasaurus , reconstructed without a macuahuitl
Size comparison of all three named parankylosaurians compared to an average human Parankylosauria Size Comparison.svg
Size comparison of all three named parankylosaurians compared to an average human

Known members of Parankylosauria are all small animals, ranging from 1.5–4.0 metres (4.9–13.1 ft), and possessed proportionally large skulls. The most distinctive trait of the group is their macuahuitl, named after the mesoamerican weapon of the same name. This trait is similar to the thagomizer of stegosaurs and tail clubs known in ankylosaurines, though evolved independently from each. This was a structure at the end of the tail formed by a series of five pairs of robust osteoderms (bones in the skin) fused together, surrounding the sides of the tail and surrounding the entirety of it near the tip. This weapon is known directly in the genus Stegouros, suspected based on indirect evidence in Antarctopelta, and not confirmed in Kunbarrasaurus, for which a complete tail is not known. In the former taxon the weapon is associated with dramatic shortening of the tail, made up of far fewer vertebrae than any other kind of thyreophoran. As with many other members of this group, osteoderms would have covered much of the body of parankylosaurs, functioning as spiny armor. [1]

Skull diagram of Kunbarrasaurus Kunbarrasaurus skull reconstruction.png
Skull diagram of Kunbarrasaurus

Parankylosaurs, compared to the more well studied euankylosaurs, retain more traits seen in more primitive thyreophorans and stegosaurs. This is most applicable in the body, most distinctively seen in the possession of rather long and slender limbs. The skull, comparatively, is more similar to that of other ankylosaurs, thought to indicate the acquisition of advanced skull traits earlier in ankylosaur evolution. Also unlike euankylosaurs, it is thought, based on the preserved osteoderms of Kunbarrasaurus and lack of flank osteoderms associated with other known genera, that parankylosaurs may not have had rather light coverings of dermal armor compared to their relatives. They possessed a pelvic shield, formed from a thin sheet of bone over the hip region, more reinforced than the superficial shielding of stegosaurs but not as overbuilt as those found in euankylosaurs. [1]

Classification

Tail vertebrae and surrounding osteoderms of Stegouros, forming its macuahuitl structure Stegouros tail.jpg
Tail vertebrae and surrounding osteoderms of Stegouros, forming its macuahuitl structure
Life restoration of Stegouros Stegouros elengassen original Luis Perez Lopez.jpg
Life restoration of Stegouros

The clade is phylogenetically defined as all taxa closer to Stegouros than to Ankylosaurus , making it a counterpart to Euankylosauria, which has the opposite definition. The following cladogram is reproduced from the phylogenetic analysis in the 2021 study by Sergio Soto-Acuña and colleagues: [1]

Lesothosaurus

Scutellosaurus

Emausaurus

Scelidosaurus

Eurypoda
Stegosauria

Huayangosaurus

Stegosauridae

Ankylosauria
Parankylosauria

Kunbarrasaurus

Antarctopelta

Stegouros

Euankylosauria

Nodosauridae

Liaoningosaurus

Gobisaurus

Shamosaurus

Ankylosaurinae

In 2022, a study by Timothy G. Frauenfelder and colleagues on a new specimen (SAMA P40536) tentatively referred to Kunbarrasaurus tested their new specimen in the dataset of the 2021 study, finding a similar placement and composition of Parankylosauria, but also coded the specimen for an older phylogenetic dataset of a 2016 paper by Victoria Arbour and Phil Currie. The resulting analysis found Kunbarrasaurus and the new specimen to nest together in a similar position on the tree to where Parankylosauria was found in the 2021 dataset, supporting that conclusion. The tree of the second dataset is reproduced below:

Lesothosaurus

Scelidosaurus

Huayangosaurus

Kunbarrasaurus

SAMA P40536

Mymoorapelta

Nodosauridae

Ankylosauridae

See also

Related Research Articles

<span class="mw-page-title-main">Thyreophora</span> Extinct clade of dinosaurs

Thyreophora is a group of armored ornithischian dinosaurs that lived from the Early Jurassic until the end of the Cretaceous.

<span class="mw-page-title-main">Ankylosauria</span> Extinct order of dinosaurs

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, similar to turtles. Ankylosaurs were bulky quadrupeds, with short, powerful limbs. They are known to have first appeared in the Middle Jurassic, and persisted until the end of the Cretaceous Period. The two main families of Ankylosaurs, Nodosauridae and Ankylosauridae are primarily known from the Northern Hemisphere, but the more basal Parankylosauria are known from southern Gondwana during the Cretaceous.

<i>Pinacosaurus</i> Genus of ankylosaurid dinosaur from Late Cretaceous

Pinacosaurus is a genus of ankylosaurid thyreophoran dinosaur that lived in Asia during the Late Cretaceous, mainly in Mongolia and China.

<i>Gastonia</i> (dinosaur) Ankylosaurian dinosaur genus from the Early Cretaceous period

Gastonia is a genus of herbivorous ankylosaurian dinosaur from the Early Cretaceous of North America, around 139 to 125 million years ago. It is often considered a nodosaurid closely related to Polacanthus. Gastonia has a sacral shield and large shoulder spikes.

<span class="mw-page-title-main">Ankylosauridae</span> Extinct family of dinosaurs

Ankylosauridae is a family of armored dinosaurs within Ankylosauria, and is the sister group to Nodosauridae. The oldest known Ankylosaurids date to around 122 million years ago and went extinct 66 million years ago during the Cretaceous–Paleogene extinction event. These animals were mainly herbivorous and were obligate quadrupeds, with leaf-shaped teeth and robust, scute-covered bodies. Ankylosaurids possess a distinctly domed and short snout, wedge-shaped osteoderms on their skull, scutes along their torso, and a tail club.

<i>Aletopelta</i> Extinct genus of dinosaurs

Aletopelta is a monospecific genus of basal ankylosaurid dinosaur from Southern California that lived during the Late Cretaceous in what is now the Point Loma Formation. The type and only species, Aletopelta coombsi, is known from a partial skeleton preserving osteoderms. It was originally described in 1996 by W. P. Coombs, Jr. and T.A. Deméré before being named in 2001 by Tracy Ford and James Kirkland. Aletopelta has an estimated size of 5 metres and weight of 2 tonnes. The holotype formed a miniature reef and was scavenged upon by invertebrates and sharks.

<span class="mw-page-title-main">Nodosauridae</span> Extinct family of dinosaurs

Nodosauridae is a family of ankylosaurian dinosaurs, from the Late Jurassic to the Late Cretaceous period in what is now North America, South America, Europe, and Asia.

Sauroplites is a genus of herbivorous ankylosaurian dinosaur from the Early Cretaceous of China.

<i>Texasetes</i> Extinct genus of dinosaurs

Texasetes is a genus of ankylosaurian dinosaurs from the late Lower Cretaceous of North America. This poorly known genus has been recovered from the Paw Paw Formation near Haslet, Tarrant County, Texas, which has also produced the nodosaurid ankylosaur Pawpawsaurus.

<i>Mymoorapelta</i> Extinct genus of ornithischian dinosaur

Mymoorapelta is a monospecific genus of nodosaurid ankylosaur, a group of heavily armored, herbivorous, quadrupedal dinosaurs, from the Late Jurassic Morrison Formation of western Colorado and central Utah, USA. Few specimens are known, but the most complete one is the holotype individual from the Mygatt-Moore Quarry that includes many osteoderms, a partial skull, vertebrae, and other bones. It was initially described by James Kirkland and Kenneth Carpenter in 1994. Along with Gargoyleosaurus, it is one of the earliest known nodosaurids.

<i>Panoplosaurus</i> Extinct genus of dinosaurs

Panoplosaurus is a genus of armoured dinosaur from the Late Cretaceous of Alberta, Canada. Few specimens of the genus are known, all from the middle Campanian of the Dinosaur Park Formation, roughly 76 to 75 million years ago. It was first discovered in 1917, and named in 1919 by Lawrence Lambe, named for its extensive armour, meaning "well-armoured lizard". Panoplosaurus has at times been considered the proper name for material otherwise referred to as Edmontonia, complicating its phylogenetic and ecological interpretations, at one point being considered to have existed across Alberta, New Mexico and Texas, with specimens in institutions from Canada and the United States. The skull and skeleton of Panoplosaurus are similar to its relatives, but have a few significant differences, such as the lumpy form of the skull osteoderms, a completely fused shoulder blade, and regularly shaped plates on its neck and body lacking prominent spines. It was a quadrupedal animal, roughly 5 m (16 ft) long and 1,600 kg (3,500 lb) in weight. The skull has a short snout, with a very domed surface, and bony plates directly covering the cheek. The neck had circular groups of plates arranged around the top surface, both the forelimb and hindlimb were about the same length, and the hand may have only included three fingers. Almost the entire surface of the body was covered in plates, osteoderms and scutes of varying sizes, ranging from large elements along the skull and neck, to smaller, round bones underneath the chin and body, to small ossicles that filled in the spaces between other, larger osteoderms.

Dracopelta is a monospecific genus of ankylosaur dinosaur from Portugal that lived during the Late Jurassic in what is now the Lourinhã Formation. The type and only species is Dracopelta zbyszewskii, which is represented by a partial skeleton including unpublished material.

<i>Antarctopelta</i> Extinct genus of dinosaurs

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 4 meters (13 ft) in length or more, and showed characteristics of two different families, making more precise classification difficult. The single known fossil specimen was discovered on James Ross Island in 1986, constituting the first dinosaur remains ever discovered on Antarctica, although it is the second dinosaur from the continent to be formally named.

<span class="mw-page-title-main">Polacanthinae</span> Extinct subfamily of dinosaurs

Polacanthinae is a subfamily of ankylosaurs, most often nodosaurids, from the Late Jurassic through Early Cretaceous of Europe and potentially North America and Asia. The group is defined as the largest clade closer to Polacanthus foxii than Nodosaurus textilis or Ankylosaurus magniventris, as long as that group nests within either Nodosauridae or Ankylosauridae. If Polacanthus, and by extent Polacanthinae, falls outside either family-level clade, then the -inae suffix would be inappropriate, and the proper name for the group would be the informally defined Polacanthidae.

<i>Zhongyuansaurus</i> Extinct genus of dinosaurs


Zhongyuansaurus is a monospecific genus of ankylosaurid dinosaur from Henan that lived during the Early Cretaceous in what is now the Haoling Formation. Zhongyuansaurus is possibly a junior synonym of Gobisaurus, a basal ankylosaurid from the Ulansuhai Formation of Inner Mongolia.

<span class="mw-page-title-main">Timeline of ankylosaur research</span>

This timeline of ankylosaur research is a chronological listing of events in the history of paleontology focused on the ankylosaurs, quadrupedal herbivorous dinosaurs who were protected by a covering bony plates and spikes and sometimes by a clubbed tail. Although formally trained scientists did not begin documenting ankylosaur fossils until the early 19th century, Native Americans had a long history of contact with these remains, which were generally interpreted through a mythological lens. The Delaware people have stories about smoking the bones of ancient monsters in a magic ritual to have wishes granted and ankylosaur fossils are among the local fossils that may have been used like this. The Native Americans of the modern southwestern United States tell stories about an armored monster named Yeitso that may have been influenced by local ankylosaur fossils. Likewise, ankylosaur remains are among the dinosaur bones found along the Red Deer River of Alberta, Canada where the Piegan people believe that the Grandfather of the Buffalo once lived.

<i>Kunbarrasaurus</i> Extinct genus of dinosaurs

Kunbarrasaurus is an extinct genus of small herbivorous ankylosaurian dinosaur from the Cretaceous of Australia.

Spicomellus is an extinct genus of herbivorous ankylosaurian dinosaur that lived in the supercontinent Gondwana during the Middle Jurassic Period. The type and only known species is Spicomellus afer, named and described in 2021. Its remains were found in the third subunit of the El Mers Group (Bathonian-Callovian), near Boulahfa, south of Boulemane, Fès-Meknès, Morocco. The genus name means "spiked collar", from the Latin 'spica' meaning spike, and 'mellum' meaning spiked dog collar and the specific name 'afer' means "the African".

<i>Stegouros</i> Extinct genus of dinosaurs

Stegouros is a genus of ankylosaurian dinosaur from the Late Cretaceous Dorotea Formation of southern Chile. The genus contains a single species, Stegouros elengassen, known from a semi-articulated, near-complete skeleton.

Patagopelta is an extinct genus of nodosaurine dinosaur from the Late Cretaceous Allen Formation of Argentina. The genus contains a single species, P. cristata, known from a partial skeleton. Patagopelta is a very small ankylosaur, comparable in size to the dwarf nodosaurid Struthiosaurus, about 2 m (6.6 ft) long.

References

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