| Liaoningosaurus | |
|---|---|
 | |
| An undescribed specimen ofLiaoningosaurus (BMNH-PH000924) on display at Beijing Museum of Natural History. | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | †Ornithischia |
| Clade: | †Thyreophora |
| Clade: | †Ankylosauria |
| Clade: | †Euankylosauria |
| Family: | †Ankylosauridae |
| Genus: | †Liaoningosaurus Xuet al., 2001 |
| Species: | †L. paradoxus |
| Binomial name | |
| †Liaoningosaurus paradoxus Xuet al., 2001 | |
| Synonyms | |
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Liaoningosaurus (meaning "Liaoning lizard") is an unusualgenus of basalankylosauriddinosaur from theLiaoning Province,China that lived during theEarly Cretaceous (lateBarremian to earlyAptian stages, ~125.4 to 118.9 Ma) in what is now theYixian andJiufotang Formation. The type and only species, Liaoningosaurus paradoxus, is known from more than 20 specimens, represented by juvenile individuals.[1] It was named in 2001 by Xu, Wang and You.
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 eatenfish. Additionally, some features of its skeleton may suggest that it was partiallyaquatic. However, not allpaleontologists agree with this interpretation. It is the oldest ankylosaurid to have had atail club and had a widepaleogeographic and stratigraphic distribution in western Liaoning. BothLiaoningosaurus andChuanqilong show various similarities with one another, with the latter being suggested to be a later growth stage.
The remains of a juvenile ankylosaur were collected by members of the Western Liaoning expedition team of theInstitute of Vertebrate Paleontology and Paleoanthropology (IVPP) from the Baicaigou locality in theLiaoning Province,China. It was recovered from the Dawangzhangzi Bed of theYixian Formation, which dates to the lateBarremian to earlyAptian stages of theEarly Cretaceous period. The specimen was named and described in2001 byXing Xu, Xiao-Lin Wang and Hai-Lu You. The generic name,Liaoningosaurus, is derived from the Liaoning Province and theGreek word "sauros" (lizard). The specific name is derived from theLatin word "paradoxus", in reference to a suite of highly unusual traits for an ankylosaur. Thetype 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.[2]
In 2016, a nearly complete skeleton ofLiaoningosaurus was described by Ji Qiang, Wu Xiaochun, Cheng Yennien, Ten Fangfang, Wang Xuri and Ji Yannan. The specimen, XHPM-1206, was collected from the Jianshangou Bed of the Yixian Formation, about 160 km west from the holotype locality. The authors noted that the specimen was slightly larger than the holotype and shows features that were either previously unknown or not accurately described in the holotype such as thehumerus being almost as long as thefemur ortibia and the presence of five digits rather than four on themanus (hand). It is currently housed at the Xinghai Museum of Paleontology.[3] Arbour & Currie (2015) referred two specimens; CYGYB 208, a nearly complete skeleton that is preserved on a slab with the dorsal (upper side) surface exposed; and CYGYB 237, a nearly complete skeleton that is preserved on a slab with the ventral (underside) surface exposed.[4]
In 2022, Chang-Fu Zhou, Qing Liu, Xinyue Wang and Honggang Zhang described a nearly complete, associated skeleton (PMOL-AD00105) ofLiaoningosaurus from theJiufotang Formation of the Liaoning Province, China. The authors considered that the presence ofLiaoningosaurus in the Jiufotang Formation supports the possibility of a widepaleogeographic andstratigraphic distribution in western Liaoning.[5] A Canadian Society of Vertebrate Palaeontology abstract book that was published in 2019 mentioned that about 20 specimens had been collected from four different localities of the Yixian Formation, and one locality from the nearby Jiufotang Formation.[6]
The type specimen ofLiaoningosaurus has an estimated length of about 34 centimetres (1 ft 1 in). It has a skull-sacral length of 17.2 centimetres (6.77 inches), while a second specimen, XHPM-1206, has a skull-sacral length of 19.3 centimetres (7.6 in). The largest specimen, GPMA-12-045, has a total body length of less than 45 centimetres (1 ft 5 in) and a skull-sacral length of 21 centimetres (8 in), and the smallest specimen, NGMC-98-003, has a preserved length of 22 centimetres (8.66 in) with a skull-sacral length of about 16 centimetres (6.299 in).[2][3] A juvenile skeleton from the Jiufotang Formation has a total estimated body length of 30 centimetres (11.8 in).[5]
The skull ofLiaoningosaurus, likeChuanqilong, may have had anantorbital fossa or fenestra, as implied by a posteriorly excavatedmaxilla. An external mandibular fenestra is also present. Thedentary bone has a straight ventral margin and has a stout appearance. On eachpremaxilla, slender teeth with few denticles are present. Premaxillary teeth are also seen in some basalnodosaurids andGargoyleosaurus.[2] There are only approximately 10 maxillary teeth, which has been suggested to be due to its juvenile status. However, the ontogenetic variation in the number of teeth is less than 10 among all known ankylosaurs. The tooth crowns are similar to those ofCrichtonsaurus (orCrichtonpelta).[7] 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.[2]
Both thescapula and humerus are slender in appearance. The scapula has a narrow scapular base and ascapular spine that may have been directed towards theglenoid. The humerus has a deltopectoral crest that extends less than half the length of the shaft. The radial condyle of the humerus is poorly developed, while the olecranon process of theulna is moderately developed. The manus is short. Xuet al. (2001) originally recorded the manual phalangeal formula as 2-3-3-2.[2] However, Jiet al. (2016) noted the presence of five digits (fingers) rather than four in one specimen ofLiaoningosaurus.[3] The femur has an indistinct femoral head and a crest-shapedtrochanter present on the mid-length of the shaft. The tibia is as long as the femur. Thepes (foot) is about 230% as long as the manus.Metatarsals II–IV are elongate, while metatarsals I and V are splint-like. The pedal phalangeal formula is 0-3-4-5-0. Both the pedal and manualunguals are triangular in dorsal view, a condition also seen inDyoplosaurus.[2]
Xuet al. (2001) noted that thesternum has a sub-trapezoidal body, a very slender posterolateral process and a straight medial margin.[2] However, Arbour & Currie (2015) questioned whether or not the sternum was preserved. The bone, tentatively identified as the left sternum, was found adjacent to various other elements and its boundaries remain unclear. The sternum could have possibly been displaced post-mortem, resulting in the anteriorly pointing posterolateral process. The sternum is dissimilar to those of other ankylosaurs, as it is not paddle-like with ovoid medial ends that narrow posterolaterally like that of nodosaurids, or fused at the midline to form a diamond shape, with narrower posterolaterally directed processes like that of ankylosaurids.[4] The preacetabular process of theilium deflects laterally and is enlarged. A crest is present on the acetabulum, which connects the ischial and pubic peduncles. Theischium is straight with a convex acetabular margin, while thepubis is strongly reduced in size.[2]
Liaoningosaurus represents the oldest ankylosaurid known to have had a tail club. Although it possessed a tail club handle, it does not appear that a tail club knob was present. The tail club in ankylosaurids refers to the entire distal structure of the ankylosaurid tail, rather than just the large terminalosteoderms. The handle consists of interlocking neural arches on the distalcaudal vertebrae, and prezygapophyses that overlap with the adjacent vertebra by at least 50% of the centrum length.[8]
With the exception of a few sub-triangular plates found near the cervical and pectoral region, it completely lacks osteoderms on its body. Xuet al. (2001) identified a large bony plate present ventral to the right pelvic girdle and noted that it was covered in small tubercles. These tubercles arehexagonal andrhombic in shape, and have a diameter of about 0.5 mm. This 'shell-like' ventral bony plate was noted as being present in no other ankylosaur.[2] Arbouret al. (2014b) re-examined and reinterpreted the ventral plate as skin impressions, with the tubercles instead representing flat polygonal scales. This reinterpretation is based mostly on the broken edges not revealing any bony histology.[9]
Given the animal's unusual anatomy, Xuet al. (2001) had trouble identifying its relationship to other ankylosaurs. Their phylogenetic analysis loosely placed it into Nodosauridae. They conceded this binary division of Ankylosauria may not be entirely sound, meaningLiaoningosaurus could represent some third lineage.[2] In 2004, paleontologist Matthew Vickaryous and colleagues left it underincertae sedis.[10] A secondcladistic analysis performed by Richard Thompson and colleagues in 2011 suggested thatLiaoningosaurus is a basal ankylosaurid.[11] This has become a consensus among phylogenetic analyses such as Arbour & Currie (2015) and Hanet al. (2014), although a reduced strict consensus performed by Frauenfelderet al. (2022) recovered it within apolytomy, along withCedarpelta andChuanqilong, that is sister clade to both Ankylosauridae and Nodosauridae.[7][4][12]
The following cladogram is based on a 2015 phylogenetic analysis conducted by Arbour and Currie:[4]
Based on the second specimen that was described in 2016, Ji and colleagues proposed thatLiaoningosaurus might have been adapted to asemiaquatic lifestyle. This is due to the presence of a 'shell-like' ventral bony plate that would have covered the entire ventral surface of the torso. The authors suggested that the structure would have functioned to protect the body from underwater attacks.[3] However, a study by Arbouret al. (2014b) examined the shell-like structure and reinterpreted it as skin impressions with no bony internal texture.[9] In contrast, Zheng (2018) suggested that the structure may have been formed by a ventral pelvic shield and an epidermal scale cover.[6] Furthermore, Ji and colleagues argued that the lack of fusion between thespine andhip bones is an adaptation to a semiaquatic lifestyle rather than a juvenile feature and the presence of open neural arch-central sutures in vertebrae cannot be used to indicate the juvenile nature of the type specimen as it is a feature also documented in young adulteosauropterygians.[3]
In addition to a semiaquatic lifestyle, the authors suggested thatLiaoningosaurus 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. They proposed three explanations as to how this association may have occurred, with the first explanation being that the fish, lying at the bottom of a lake or river, passively went into the ribcage due to underwater turbulence. The second explanation suggests that the fish died whilst within the ribcage when they were scavenging, while the third explanation is that the fish represent gut contents. 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. The fish skeletons are scattered on both sides of the body cavity instead of being tightly packed in the stomach region, which may have been caused by the expulsion of gases or the compression of the stomach region post-mortem. In addition to fish, the tail of a lizard is preserved on the posterolateral side of the ribcage.[3]
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).[13]
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.[4] In addition, Hanet al. (2014) also considered the unfused scapula and coracoid, low and wedge-shaped olecranon process of the ulna, and unfused calcaneum and astragalus of the holotype to be juvenile characteristics.[7] However, Jiet al. (2016) argued that the holotype, and other specimens, instead represented adults due to the lack of fusion of the ribs to the vertebrae, absence of a synsacrum, and small stature of all known specimens.[3] Amicroanatomical study by Chinese palaeontologist Wenjie Zheng instead concluded that the holotype was no older than 12 months and further suggested thatLiaoningosaurus could be the juvenile form of the much largerChuanqilong. In 2019, Li Xiaobo and Robert R. Reisz investigated three more specimens and also concluded they represented juveniles.[6] Zhenget al., (2025) concluded that all specimens ofLiaoningosaurus found so far were under a year old at the time of their deaths through bone histology.[1]
Specimens attributable toLiaoningosaurus have been recovered from the Dawangzhangzi and Jianshangou Beds of the Yixian Formation, which is a part of theJehol Biota. The Yixian Formation is mainly composed ofvolcanic rocks such asandesites, andesitebreccia,agglomerates andbasalts.[14] It represents a freshwaterlacustrine environment, lacking rivers and deltas among other variable features of freshwater settings. Such environments lacking these features include shallow lakes.[15] The yearly temperature averaged about 10 °C (50 °F) and was temperate, with distinct wet and dry seasons.[16] The fluctuations in the climate are due toorbital forcing.[17]Conifers related to species that are found in modern subtropical and temperate upland forests dominated the landscape, withferns,cycads,horsetails, and a small number offlowering plants also being present.[16][15] Previous dating using40Ar-39Ar isotopes gave an age of approximately 125 to 120 Ma, although more recent estimates indicate an age of 125.755 ± 0.061 to 124.122 ± 0.048 ma by using U-Pb zircon.[18][19] The deconstruction and reconstruction of biotic components occurred frequently due to periodic mortality events such as volcanic eruptions,wildfires, andnoxious gases erupting from the lakes.[18]
Fossils ofgastropods,bivalves,ostracods,insects,amphibians,pterosaurs,dinosaurs,birds andmammals have been recovered from the Yixian Formation. Ornithischians from the formation are represented by the hadrosauroidsBolong andJinzhousaurus; the ceratopsianPsittacosaurus; and the basal neornithischianJeholosaurus. Saurischians include the sauropodsDongbeititan andLiaoningotitan; the dromaeosauridsSinornithosaurus andTianyuraptor; the troodontidsMei andSinovenator; the therizinosaurBeipiaosaurus; the oviraptorosaursCaudipteryx andIncisivosaurus; the ornithomimosaursHexing andShenzhousaurus; the compsognathidSinosauropteryx; and the tyrannosaursDilong andYutyrannus.
One specimen ofLiaoningosaurus was retrieved from the Jiufotang Formation of the Jehol Group. It overlies the Yixian Formation, and is composed ofmudstones,siltstones,shales,sandstones andtuffs. Similar to the Yixian Formation, it represents a lacustrine environment lackingrivers anddeltas. The Jiufotang Formation experienced less volcanism compared to its underlying formation, and fluctuated seasonally betweensemi-arid andmesic conditions.[15] 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.[20] Zhouet al. (2022) suggested that the Jehol ecosystem (the Yixian and Jiufotang Formations) may have been more suitable for the survival of juvenile ankylosaurs based on the lack of adult specimens and abundance of juvenile specimens.[5]
The Jiufotang Formation has yielded specimens of the basal ankylosauridChuanqilong, the ceratopsianPsittacosaurus, the dromaeosauridMicroraptor, the oviraptorosaurSimilicaudipteryx, the jeholornithiformsJeholornis andKompsornis, and the tyrannosaurSinotyrannus. Other vertebrate fossils found in the formation included fish, mammaliamorphs such asFossiomanus andLiaoconodon, the choristoderansPhilydrosaurus andIkechosaurus, pterosaurs likeLiaoningopterus,Sinopterus, andGuidraco, enantiornithines such asLongipteryx,Sinornis andYuanchuavis, and a variety of early birds likeYanornis andYixianornis.
