L. paradoxus was unusual among ornithischian dinosaurs in that it is speculated to have hunted or scavenged, with preserved gut contents showing that it may have eaten fish.

The specific name is derived from the Latin word "paradoxus", in reference to a suite of highly unusual traits for an ankylosaur.

The type specimen, IVPP V12560, consists of a nearly complete, articulated skeleton measuring approximately 34 centimetres (1 ft 1 in) in length that was preserved with the ventral surface exposed on a slab.

[3] In 2022, Chang-Fu Zhou, Qing Liu, Xinyue Wang and Honggang Zhang described a nearly complete, associated skeleton (PMOL-AD00105) of Liaoningosaurus from the Jiufotang Formation of the Liaoning Province, China.

The authors considered that the presence of Liaoningosaurus in the Jiufotang Formation supports the possibility of a wide paleogeographic and stratigraphic distribution in western Liaoning.

[6] The teeth have a shelf-like cingulum at their bases, and a palmate crown which bears vertical flutes that coincide with the notches between marginal cusps.

Xu et al. (2001) identified a large bony plate present ventral to the right pelvic girdle and noted that it was covered in small tubercles.

[1] Arbour et al. (2014b) re-examined and reinterpreted the ventral plate as skin impressions, with the tubercles instead representing flat polygonal scales.

[6][3][11] The following cladogram is based on a 2015 phylogenetic analysis conducted by Arbour and Currie:[3] Gastonia Ahshislepelta Aletopelta Liaoningosaurus Cedarpelta Chuanqilong Gobisaurus Shamosaurus Crichtonpelta Tsagantegia "Zhejiangosaurus" Pinacosaurus grangeri Pinacosaurus mephistocephalus Saichania Tarchia Zaraapelta Dyoplosaurus Talarurus Nodocephalosaurus Ankylosaurus Anodontosaurus Euoplocephalus Scolosaurus Ziapelta Based on the second specimen that was described in 2016, Ji and colleagues proposed that Liaoningosaurus might have been adapted to a semiaquatic lifestyle.

[2] In addition to a semiaquatic lifestyle, the authors suggested that Liaoningosaurus was carnivorous based on the elongated and fork-like denticles of the crowns of the cheek teeth, sharp unguals on the hands and feet, and the presence of fish within the skeleton of the second specimen.

The authors considered the third explanation to be the most reasonable, arguing that the obscure body outline and incompleteness of the fish being was caused by digestive acids.

[2] Paleontologist Andrea Cau has expressed skepticism on the idea, considering it too radical in view of the actual evidence, which could be explained by more parsimonious interpretations: reduced ossification of the skeleton and small size are typical traits of juveniles, and abundance of juvenile individuals compared to the adults is coherent with what is known of Mesozoic dinosaurs population dynamics and of high conservation deposits.

Also, the aquatic depositional setting in which the specimen was found doesn't necessarily mean the animal itself was aquatic (many other dinosaurs have been found in such contexts) and the chaotic distribution of fish inside the thoracic cavity, and the presence of one outside of it, are more coherent with fish scavenging on the animal's carcass (it would also be expected that, given the abundance of specimens, more showed evidence of a supposedly piscivorous diet, but such is not the case).

[12] Arbour and Currie (2015) considered the type specimen to represent a juvenile individual on basis of unfused neural arches, small size and the absence of post-cervical osteoderms.

[2] A microanatomical study by Chinese palaeontologist Wenjie Zheng instead concluded that the holotype was no older than 12 months and further suggested that Liaoningosaurus could be the juvenile form of the much larger Chuanqilong.

[5] Specimens attributable to Liaoningosaurus have been recovered from the Dawangzhangzi and Jianshangou Beds of the Yixian Formation, which is a part of the Jehol Biota.

[16] Conifers related to species that are found in modern subtropical and temperate upland forests dominated the landscape, with ferns, cycads, horsetails, and a small number of flowering plants also being present.

[17] Fossils of gastropods, bivalves, ostracods, insects, amphibians, pterosaurs, dinosaurs, birds and mammals have been recovered from the Yixian Formation.

Saurischians include the sauropods Dongbeititan and Liaoningotitan; the dromaeosaurids Sinornithosaurus and Tianyuraptor; the troodontids Mei and Sinovenator; the therizinosaur Beipiaosaurus; the oviraptorosaurs Caudipteryx and Incisivosaurus; the ornithomimosaurs Hexing and Shenzhousaurus; the compsognathid Sinosauropteryx; and the tyrannosaurs Dilong and Yutyrannus.

[14] Based on analyses using secondary ion mass spectrometry (SIMS) zircon U-Pb, the formation dates to the late Barremian and Aptian stages of the Lower Cretaceous period, approximately 122.0–118.9 Ma.

[4] The Jiufotang Formation has yielded specimens of the basal ankylosaurid Chuanqilong, the ceratopsian Psittacosaurus, the dromaeosaurid Microraptor, the oviraptorosaur Similicaudipteryx, the jeholornithiforms Jeholornis and Kompsornis, and the tyrannosaur Sinotyrannus.

Other vertebrate fossils found in the formation included fish, mammaliamorphs such as Fossiomanus and Liaoconodon, the choristoderans Philydrosaurus and Ikechosaurus, pterosaurs like Liaoningopterus, Sinopterus, and Guidraco, enantiornithines such as Longipteryx, Sinornis and Yuanchuavis, and a variety of early birds like Yanornis and Yixianornis.