A New Basal Hadrosauroid Dinosaur (Dinosauria: Ornithopoda) with Transitional Features from the Late Cretaceous of Henan Province, China

<div><p>Background</p><p>Southwestern Henan Province in central China contains many down-faulted basins, including the Xixia Basin where the Upper Cretaceous continental sediments are well exposed. The Majiacun Formation is a major dinosaur-bearing stratigraphic unit that occurs in this basin.</p><p>Methodology/Principal Findings</p><p>A new basal hadrosauroid dinosaur, <i>Zhanghenglong yangchengensis</i> gen. et sp. nov., is named based on newly collected specimens from the middle Santonian Majiacun Formation of Zhoujiagou Village, Xixia Basin. Two transitional features between basal hadrosauroids and hadrosaurids are attached to the diagnosis of the new taxon, namely five maxillary foramina consisting of four small scattered ones anteroposteriorly arranged in a row and a large one adjacent to the articular facet for the jugal, and dentary tooth crowns bearing both median and distally offset primary ridges. <i>Zhanghenglong</i> also displays a unique combination of plesiomorphic and derived features of hadrosauroids, and is clearly morphologically transitional between basal hadrosauroids and hadrosaurids. Furthermore, some measurement attributes in osteology are applied to the quantitative analysis of <i>Zhanghenglong</i>. For these attributes, the partition of the dataset on most hadrosauroid species resulting from model-based cluster analysis almost matches taxonomic separation between basal hadrosauroids and hadrosaurids. Data of <i>Zhanghenglong</i> on selected measurement attributes straddle the two combinations of intervals of partitioned datasets respectively related to basal hadrosauroids and hadrosaurids. This condition is similar to mosaic evolution of morphological characters present in the specimens of the taxon. The phylogenetic analysis of Hadrosauroidea recovers a clade composed of <i>Zhanghenglong</i>, <i>Nanyangosaurus</i>, and Hadrosauridae with an unresolved polytomy.</p><p>Conclusions/Significance</p><p><i>Zhanghenglong</i> is probably a relatively derived non-hadrosaurid hadrosauroid, based on the inferences made from the morphological comparisons, quantitative evaluation of measurements, and cladistic analysis. In combination with information on the stratigraphy, phylogeny and biogeography, the material of <i>Zhanghenglong</i> provides direct evidence for the hypothesis that hadrosaurids might have originated in Asia.</p></div

Maxillary and dentary teeth of <i>Zhanghenglong yangchengensis</i>.

<p>(A) Teeth of the right maxilla (XMDFEC V0013, holotype) in labial view. (B) Teeth of the right dentary (XMDFEC V0013, holotype) in lingual view.</p

Simplified geographic map and detailed stratigraphic section showing the locality and horizon of <i>Zhanghenglong yangchengensis</i>.

<p>(A) Geographic map showing the down-faulted basins and depressions (dark grey areas) of southwest Henan Province, China where Upper Cretaceous continental sediments are well developed and the locality of <i>Z. yangchengensis</i> (the black five-pointed star) in the Xixia Basin. (B) Stratigraphic section of the Zhoujiagou outcrop that represents most of the middle portion (Unit 2) of the Majiacun Formation and the upper part of the lower portion (Unit 1) of the same formation, with the horizon of <i>Z. yangchengensis</i> indicated by an arrow. (C) Excavation of the Zhoujiagou locality in 2011.</p

Comparison of the primary ridges of the tooth crowns in the dentary dental batteries of some hadrosauroid species (all dental batteries in lingual view).

<p>(A) <i>Equijubus normani</i> (IVPP V12534). (B) <i>Probactrosaurus gobiensis</i> (PIN 2232/42-1). (C) <i>Bactrosaurus johnsoni</i> (AMNH 6553). (D) <i>Parasaurolophus tubicen</i> (NMMNH P-25100). (E) <i>Edmontosaurus regalis</i> (CMN 2289). (F) <i>Brachylophosaurus canadensis</i> (CMN 8893).</p

Strict consensus of 405 most parsimonious trees recovered from the cladistic analysis of Hadrosauroidea, with the participation of <i>Hadrosaurus foulkii</i> (the characters associated with the laterodistal corner of the deltopectoral crest were coded as polymorphic for <i>Brachylophosaurus</i>, <i>Shantungosaurus</i>, and <i>Edmontosaurus</i>).

<p>Strict consensus of 405 most parsimonious trees recovered from the cladistic analysis of Hadrosauroidea, with the participation of <i>Hadrosaurus foulkii</i> (the characters associated with the laterodistal corner of the deltopectoral crest were coded as polymorphic for <i>Brachylophosaurus</i>, <i>Shantungosaurus</i>, and <i>Edmontosaurus</i>).</p

Reconstruction and restoration of the skeleton of <i>Zhanghenglong yangchengensis</i>.

<p>(A) Skull reconstruction of <i>Z. yangchengensis</i> in left lateral view. (B) Restoration of the head and the anterior part of the neck of <i>Z. yangchengensis</i> in left lateral view. (C) Skeleton reconstruction of <i>Z. yangchengensis</i> in left lateral view. Bones in white are preserved in the specimens of <i>Z. yangchengensis</i> (XMDFEC V0013 and V0014). Bones in grey are unknown. Abbreviations: d, dentary; f, frontal; j, jugal; l, lacrimal; mx, maxilla; na, nasal; pd, predentary; pmx, premaxilla; po, postorbital; prf, prefrontal; q, quadrate; qj, quadratojugal; sa, surangular; sq, squamosal.</p

Anterior-middle dorsal vertebrae of <i>Zhanghenglong yangchengensis</i>.

<p>Four dorsal vertebrae probably representing D4–D7 orderly (XMDFEC V0014, paratype) in anterior (A, D, G, J), posterior (B, E, H, K), and left lateral (C, F, I, L) views.</p

Measurements for the anterior dorsal vertebrae (D1 and D4–D7) of <i>Zhanghenglong</i> (in mm).

<p>Measurements for the anterior dorsal vertebrae (D1 and D4–D7) of <i>Zhanghenglong</i> (in mm).</p

Bayesian Information Criterion (BIC) plots showing the results of model-based cluster analysis (MCA) implemented in Mclust for the datasets consisting of the values of most hadrosauroids and some basal iguanodontians on six selected measurement attributes (MA) derived from some phylogenetic characters, with the corresponding simplified box plots of the datasets showing the detached intervals respectively related to basal hadrosauroids and hadrosaurids.

<p>BIC plot (A) and box plot (B) for MA1. BIC plot (C) and box plot (D) for MA2. BIC plot (E) and box plot (F) for MA3. BIC plot (G) and box plot (H) for MA4. BIC plot (I) and box plot (J) for MA5. BIC plot (K) and box plot (L) for MA6. Abbreviations: BH, basal hadrosauroids; BI, basal iguanodontians outside of Hadrosauroidea; H, hadrosaurines; L, lambeosaurines.</p

Dentary of <i>Zhanghenglong yangchengensis</i>.

<p>Right dentary (XMDFEC V0013, holotype) in lateral (A), medial (B), dorsal (C), and posterior (D) views.</p