Liaoningosaurus

Liaoningosaurus Temporal range: Early Cretaceous,
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Superorder:	Dinosauria
Order:	Ornithischia
Suborder:	Thyreophora
Infraorder:	Ankylosauria
Family:	?Nodosauridae
Genus:	Liaoningosaurus Xu, Wang & You, 2001
Species
L. paradoxus Xu, Wang & You, 2001 (type)

Liaoningosaurus is a very unusual ankylosaur from the Lower Cretaceous. The holotype (IVPP V12560; Institute of Vertebrate Paleontology and Paleoanthropology, Beijing), an essentially complete juvenile skeleton compressed on a slab, was collected from the Yixian Formation (Aptian) of Liaoxi, Yixian County, Liaoning Province, People's Republic of China.

The type species Liaoningosaurus paradoxus was in 2001 named by Xu Xing, Wang Xiaolin and You Hailu. The generic name refers to Liaoning. The specific name refers to the confusing mix of nodosaurid and ankylosaurid features shown by the specimen.

The articulated skeleton measures approximately 34 cm in length, giving it the distinction of being the smallest-known ankylosaur specimen. The specimen is unique among all known ankylosaur fossils in the retention of the external mandibular fenestra. Antorbital fenestrae may also be present. Both are likely juvenile traits, just as the relatively large teeth, the retention of teeth in the praemaxilla, long feet, long lower legs and the possession of long sharp claws on the hand and feet. A real feature unique to the taxon, or autapomorphy might be the trapezoid form of the breast bone

Another new feature is the presence of ventral armor plating, two very large paired osteoderms covering the entire abdomen and having a surface structure sculpted with small hexagonal and rhombic elevations. Such plates had never been found with other ankylosaurians, of which the belly armor is poorly known, however. Smaller triangular osteoderms were found on the shoulder, the scapula showing the onset of a shoulder spike.

Determining the relations of Liaoningosaurus is difficult because of the young age of the specimen individual and the presence of traits both typical of ankylosaurids and nodosaurids. Xu et al. (2001) published a cladistic analysis, placing Liaoningosaurus basal within the Nodosauridae, while Vickaryous et al. (2004) have provisionally assigned it to the Ankylosauria incertae sedis.

References

• Xu, X., Wang, X.-L., and You, H.-L. (2001). "A juvenile ankylosaur from China". Naturwissenschaften 88(7): 297-300.
• Vickaryous, Maryanska, and Weishampel (2004). "Ankylosauria". in The Dinosauria (2nd edition), Weishampel, D. B., Dodson, P., and Osmólska, H., editors. University of California Press.