Liaoningosaurus

Credit: Studio 252MYA.

*Liaoningosaurus* is an extinct genus of Ankylosaurian dinosaur that lived in Liaoning, China during the Early Cretaceous.

## History

IVPP V12560, the holotype, is an articulated skeleton 34 centimeters (1 foot, 1 inche) long from the Early Cretaceous-aged Yixian Formation, Liaoning Province, China. In 2001, *L. paradoxus* was described. The genus name was coined after the Liaoning Province and the species name referenced how it was a "paradox" among ankylosaurs. It was first interpreted as a juvenile, since the vertebral centra and neural arches were unfused. Hwever, in 2016, JiQiang suggested it was an adult, which had unusual aquatic adaptations.  This would make *Liaoningosaurus* the smallest ornithischian dinosaur and only aquatic/semi-aquatic thyreophoran, if correct. In 2018, a microanatomical study by Wenjie Zheng concluded the holotype was no older than 12 months. In 2019, Li Xiabo and Robert R. Reisz examined 3 more individuals, who were concluded juveniles. ~20 specimens were collected from Yixian rocks from 4 localities, one from the nearby Jiufotang Formation. Many are undescribed.

## Description

—Jim Kirkland teasing research on *L. paradoxus*
*Liaoningosaurus* is a unique ankylosaur, retaining the external mandibular fenestra. Additionally, antorbital fenestrae may be present. Teeth in *Liaoningosaurus* are relatively large, having teeth in the praemaxilla (either a primitive or premature trait), with the points on the tooth crown being strangely long and sharp, forming a sort of "fork". Its feet are long, with long lower legs and long, sharp claws on all feet. This is different from the blunt claws observed in most ankylosaurians. At first, they were all thought to represent juvenile features, since it was small and the spine and hip were unfused. Additionally; the data collected from specimen 2 revealed it potentially has noticeable semi-aquatic adaptations. The large teeth and claws may have aided in small prey capture, similiar to trapjaw turtles; with the stomach of specimen 2 showing a gut full of fish remains. It could have been carnivorous, or at least omnivorous, the first ornithischian to have this lifestyle, though this is suspected in basal ornithischians (such as heterodontosaurs and pachycephalosaurs).

A supposedly unique feature is armour plating on the underside of the holotype. It is a large segment, appearing to be bone, layered with small hexagonal and rhombic bumps. This is not found in other ankylosaurs. If Liaoningosaurus was truly semi-aquatic, this could have protected it from predation, like in modern turtles. Small triangular osteoderms were observed in the shoulder alongside a small spike. Closer examination of these bumps show they were not a part of a singular structure, but were similar to scales. The broken edges of the "plates" did not reveal an internal structure, as expected by a piece of bone, when examined by Victoria Arbour et al. (2013). They found the "belly plates" were preserved skin.

Currently unofficially published, several users online (including Jim Kirkland) have noticed *Liaoningosaurus* teeth are very similar to marine iguanas and other algae-grazing animals. Thus, *Liaoningsaurus* may also fed on algae; concluding an omnivorous diet. Jim Kirkland may be publishing phylogenetic research on this soon, however, stating he will be using "feeding behaviour and morphological models, [combined] with phylogenetic relationships [that] should be informative".

## Classification

Determining the relations of *Liaoningosaurus* is difficult because it is immature and traits seen in Nodosauridae and Ankylosauridae. Xu et al. (2001) published a cladistic analysis, placing it in Nodosauridae. Vickaryous et al. (2004) had assigned it to Ankylosauria incertae sedis. Thompson et al. (2011) published another cladistic analysis, finding *Liaoningosaurus* was an extremely basal ankylosaurid. Zheng (2018) suggested it was the juvenile form of *Chuanqilong*, also known from the Jiufotang Formation.

## References

* https://blogs.scientificamerican.com/laelaps/this-tiny-ankylosaur-ate-fish/
* https://twitter.com/Paleojim/status/1421135257508540416
* http://en.cnki.com.cn/Article\_en/CJFDTotal-JSDZ201602028.htm
* https://eartharchives.org/articles/armored-dinosaur-was-a-fish-eating-turtle-mimic/index.html
* https://link.springer.com/article/10.1007%2Fs001140100233
* https://en.wikipedia.org/wiki/Liaoningosaurus