A new saurolophine hadrosaurid (Dinosauria: Ornithopoda) from the Upper Cretaceous of Shandong, China

Abstract

A new saurolophine hadrosaurid, Laiyangosaurus youngi gen. et sp. nov. is described and phylogenetically analyzed based on several cranial elements from the Jingangkou Formation, Wangshi Group, Upper Cretaceous of Laiyang, Shandong, China. Laiyangosaurus youngi differs from other members of the saurolophine clade on the basis of a number of autapomorphies, including a prominent and narrow ridge on the lateral side of the nasal which forms the posterodorsal and posterior margin of the circumnasal depression, a primary ridge that runs along most of the maxillary tooth row that is slightly deflected posteriorly, a retroarticular process of the surangular that is dorsolateroposteriorlly recurved, and orbital margins that are wider than the infratemporal margins of the jugal. This new taxon can be further distinguished by a number of unique combination of characters, including dorsal margin of nasal is flat, absence supracranial crest, a relatively shallow and rostrodorsally directed caudal margin of the lacrimal process of the jugal, and one or more foramina present on the rostral surface of the premaxilla. A phylogenetic analysis indicates that L. youngi comprises a monophyletic clade, which is known as Edmontosaurini.

A New Hadrosaurine (Dinosauria: Hadrosauridae) from the Marine Deposits of the Late Cretaceous Hakobuchi Formation, Yezo Group, Japan

“…One of four unambiguous synapomorphies for the clade of Edmontosaurini (one rounded knob of marginal denticles of dentary teeth) is preserved in Kamuysaurus . Within the clade of Edmontosaurini, Kamuysaurus forms a monophyly with Laiyangosaurus 55 and Kerberosaurus , sharing four unambiguous synapomorphies. Two of these synapomorphies (moderate ventral deflection of the rostral dentary and strong medial deflection of the caudal process of the surangular) are commonly seen in lambeosaurines, whereas a similar width of orbit and infratemporal fenestra is seen in the members of Kritosaurini, and slight ventral deflection of the preacetabular process of the ilium is a primitive feature for hadrosauroids.…”

Re-examination of the cranial osteology of the Arctic Alaskan hadrosaurine with implications for its taxonomic status

“…As Mori et al [36] pointed out, the maxillae are relatively low, with a height approximately 34% of anteroposterior length measured along the oral margin. This proportion, which is negatively allometric among Edmontosaurini (Fig 2C and S2 Table), resembles that of Laiyangosaurus youngi [51].…”

“…Alternatively, since a lambeosaurine is now recognized in the Prince Creek Formation [10], the feature shared with derived lambeosaurines Corythosaurus and Hypacrosaurus may simply indicate that this element belongs to a member of Lambeosaurinae, although it also has a hadrosaurine feature (see description section). The anteroposteriorly long maxilla is unique to the PCF hadrosaurine and Laiyangosaurus youngi [51].…”

“…The premaxilla bears the bony external naris (DMNH 22716, UAMES 12995), a gracile posterodorsal process (DMNH 22716), and distinct circumnarial ridge (UAMES 12995) as is typical in hadrosaurines (Fig 1). The oral margin of the premaxilla is deflected posterodorsally and forms a prominent lip-like structure (UAMES 12995) that resembles Edmontosaurus annectens (e.g., CMN 8509, ROM 57100), Edmontosaurus regalis (e.g., CMN 2288, ROM 00801), Laiyangosaurus youngi [51], and Shantungosaurus [35,52]. The anterodorsal surface of the lip-like structure is perforated by several small foramina (DMNH 22716, UAMES 12995).…”

“…Therefore, the elongated maxilla of the PCF Edmontosaurus is the only feature that may be reasonably different from the other members of Edmontosaurus (Table 1). However, this feature might prove inadequate to diagnose the taxon since an anteroposteriorly-elongated maxilla is also present in another member of the Edmontosaurini, Laiyangosaurus youngi [51]. For the reasons listed above, the validity of the species "kuukpikensis" is left as questionable and unresolved.…”