A New Basal Hadrosauroid Dinosaur from the Lower Cretaceous Khok Kruat Formation in Nakhon Ratchasima Province, Northeastern Thailand

Abstract

A new basal hadrosauroid dinosaur from the Lower Cretaceous Khok Kruat Formation of Thailand, Sirindhorna khoratensis gen. et sp. nov is described. The new taxon is based on composite skull and mandible including premaxilla, maxilla, jugal, quadrate, braincases, predentary, dentaries, surangular, and maxillary and dentary teeth. It is diagnostic by such characters as, sagittal crest extending along entire dorsal surface of the parietal and reaching the frontoparietal suture (autapomorphy), transversely straight frontoparietal suture, caudodorsally faced supraoccipital, no participation of the supraoccipital in the foramen magnum, mesiodistally wide leaf-shaped dentary tooth with primary and secondary ridges on the lingual surface of the crown, perpendicularly-erected and large coronoid process of dentary, and nonvisible antorbital fossa of the maxilla in lateral view. Phylogenetic analysis revealed S. khoratensis as among the most basal hadrosauroids. Sirindhorna khoratensis is the best-preserved iguanodontian ornithopod in Southeast Asia and sheds new light to resolve the evolution of basal hadrosauriforms.

The Dinosaurian Ichnofauna of the Lower Cretaceous (Valanginian–Barremian) Broome Sandstone of the Walmadany Area (James Price Point), Dampier Peninsula, Western Australia

“…Accounting for the presence of large-bodied hadrosauroids in Australia during the Early Cretaceous is difficult. Hadrosauroids first diversified in uppermost Lower Cretaceous of Asia and to a lesser extent North America (Prieto-M arquez, 2010; Shibata et al, 2015). Thus far, the only confirmed record of hadrosauroids from the Gondwanan landmasses are four taxa of 'kritosaurs' from the upper Campanian-Maastrichtian of Argentina (Bonaparte et al, 1984;Bonaparte and Rougier, 1987;Coria, 2011;Coria et al, 2012): Secernosaurus koerneri, 'Kritosaurus' australis, Willinakaqe salitralensis, and Lapampasaurus cholinoi, along with some indeterminate specimens of lambeosaurines (Brett-Surman, 1979;Bonaparte et al, 1984;Ju arez Valieri et al, 2010;Prieto-M arquez and Salinas, 2010;Coria, 2011).…”

A new styracosternan hadrosauroid (Dinosauria: Ornithischia) from the Early Cretaceous of Portell, Spain

“…Even if, a small fragment of a juvenile right dentary (MPG-SCH-10) it has been considered by Verdú et al [ 7 ] as a paratype of Iguanodon galvensis . The ventral and dorsal edges of the fossil diverge rostrally, developing a deep-rostral end as in Ouranosaurus [ 31 ], and Sirindhorna [ 30 ]. Conversely, the ventral and dorsal edges of Portellsaurus sosbaynati are parallel.…”

“…Diagnosis of genus and species by monotypy. Styracosternan hadrosauroid distinguished by two autapomorphies: the absence of a bulge along the ventral margin directly ventral to the base of the coronoid process, convergent with the two more derived hadrosauroids Altirhinus kurzanovi [29] and Sirindhorna khoratensis [30], and the presence of a deep oval cavity on the medial surface of the mandibular adductor fossa below the eleventh-twelfth tooth position. Internally, the cavity connects with the last nutrient foramina (the most caudal).…”

Anatomy, taphonomy, and phylogenetic implications of a new specimen of Eolambia caroljonesa (Dinosauria: Ornithopoda) from the Cedar Mountain Formation, Utah, USA

“…In contrast to these small, geographically and temporally restricted clades, a widespread and long-lived novel clade of basal hadrosauroids also was recovered by this analysis. This clade consists of taxa from North Africa ( Ouranosaurus [ 59 ]), Europe ( Morelladon [ 100 ] and Proa [ 41 ]), and Asia ( Altirhinus [ 67 ], Batyrosaurus [ 14 ], Koshisaurus [ 45 ], and Sirindhorna [ 101 ]). Most members of this clade are of Early Cretaceous age (Barremian–Albian); however, if the Santonian age of Batyrosaurus proposed by Godefroit et al [ 14 ] is accurate, then this clade persisted into the Late Cretaceous.…”