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.
Highlights
Fossil records of non-hadrosaurid hadrosauriform dinosaurs in Asia have been accumulated in this century [1,2,3,4,5,6,7,8,9,10,11]
Well-preserved iguanodontian specimens were restricted in China and Mongolia; for instance, Jinzhousaurus yangi was known as the almost complete articulated skeleton
Found from Liaoning Province [6], Xuwulong yueluni was represented by an articulated skeleton without appendages from Gansu Province of China [11], and Probactrosaurus gobiensis from Inner Mongolia was described including several individuals of cranium and post cranial portions [5]
Summary
Fossil records of non-hadrosaurid hadrosauriform dinosaurs in Asia have been accumulated in this century [1,2,3,4,5,6,7,8,9,10,11]. The new taxon in this study is known from extensive remains including a disarticulated skull and mandibles, and is much more complete than material of the aforementioned Thailand iguanodontians This new material was collected from one locality of the Lower Cretaceous Khok Kruat Formation during the first term of Japan-Thailand Dinosaur Project (abbreviated as JTDP), including the preliminary excavation by NRRU in 2005. We describe this material and discuss its phylogenetic position based on a cladistic analysis. The electronic edition of this work was published in a journal with an ISSN, and has been archived and is available from the following digital repositories: PubMed Central, LOCKSS
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