[D] Changchunsaurus parvus [Su] [sG] [T]
Zan, Chen, Jin, and Li, 2005
Ornithischia Ornithopoda Incertae Sedis
Quantou Formation, Songliao Basin, Shanqian, Liufangzi, Gongzhuling City, Central Jilin Province, China.
Genus - Typespecies - Skull
A very primitive ornithopod, , with 5 premaxillary teeth, very short edentulous portion of the premax, a short diastema, premax margin even with that of the maxilla, a jugal boss, and something called a \\\\\\\"nubble structure\\\\\\\" on the jugal.
A new ornithopod Changchunsaurus parvus gen. et sp. nov.dinosaur is named and described on the basis of a specimen from the Early Cretaceous Quantou Formation at Liufangzi locality, Jilin Province, China. The specimen represents the first primitive ornithopod taxon from the Cretaceous deposits in the Songliao Basin.
Changchunsaurus is an interesting ornithopod in having a combination of primitive and derived characters. It shares with some ornithopod autopomorphies: paroccipital process is crescent shaped, the jaw articulation offsets ventral to the maxillary tooth row. It shares with euornithopods the following synapomorphies: antorbital fenestra small, external mandibular fenestra absent. However, It is believed that Changchunsaurus is also more primitive than most of ornithopods and marginocephalians in having five premaxillary teeth, a short edentulous anterior portion of premaxilla, a short diastema between premaxillary and maxilla teeth, the enamel on crowns of maxilla teeth and dentary teeth distribute symmetrically, and the premaxillary bill margin is level with that of the maxilla.
Its jugal boos projects lateral face of the jugal. There is nubble structure on the lateral expansion of jugal, which is not described in other ornithopods . Changchunsaurus has a long predentary, which suggests it might have an immobile mandibular symphysis as in ceratopians , and the predentary ventral process is longer than the lateral process. It is similar to derived ornithopodas in the morphology of the predentary with bilobate ventral process end. Further work is needed to give precise phylogenetic relationship of the new ornithopod.
Order Ornithischia Seeley, 1888 Suborder Ornithopoda Marsh, 1881 Family Incertae sedis Changchunsaurus gen. nov.
Type species: Changchunsaurus parvus gen. et sp. nov.
JLUM L0403-j–Zn2, a skeleton with complete skull.
Genus name refers to ‘Changchun’, the capital of Jilin Province, where the type specimen was collected. Species name: ‘parvus’ means petite, refers to the small size of the dinosaur.
JLUM L0204-Y-23, a premaxilla that the left posterolateral process and the end of the dorsal process were broken. JLUM L0204-Y-24, an almost complete right dentary.
Changchunsaurus parvus is a small ornithopod of about 1m long with a skull that is about 11.5cm in length. It has a short preorbital skull segment less than 40% of the skull length. A longitudinal concave is present along the midline of the nasal. The contact between the posterolateral premaxillary process and the lacrimal is absence.
The ventral margin of the premaxilla is on the same level with that of the maxilla, and the diastema between the premaxillary and maxillary teeth is short about one tooth length. The depression for M. buccinatoris on the maxilla and dentary is obvious. It has a small antorbital fenestra and a large orbit about one third of the skull length. The orbit is posterolaterally situated and is somewhat ellipse-shaped. The palpebral is stout.
The jugal is relatively shallow. A jugal boos projects laterally close to the ventral margin of the orbit near the middle part of the jugal, and has nubble structure on the surface. The quadratojugal is more or less triangular. The quadrate foramen is absent. The quadrate is robust and slopes caudodorsally, it has a broad and very shallow concave on the lateral surface along its midline.
The jaw articulation is below the occlusal plane of the teeth. The retroarticular process is well-developed. The mandible has a high coroniod process and lacks the external mandibular fenestra. The predentary is long and its anterior portion is sharp. The ventral process of the predentary is longer than the lateral process, and the end of the ventral process is bilobate. Dental Formula .
The premaxillary tooth is canine-shaped and recurved, and the thick enamel is on the premaxillary tooth crowns. The enamel on crowns of maxilla teeth and dentary teeth distribute symmertrically. Maxillary teeth are buccolingually compressed. The maxillary tooth crowns bear several small vertical ridges, with the wear towards the lingual face. The dentary tooth crowns are somewhat diamond shaped. The dentary tooth crowns have a strong vertical median ridge and several weaker secondary ridges, with the wear facets towards the buccal face.