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

Shibata M, Jintasakul P, Azuma Y, You HL - PLoS ONE (2015)

Bottom Line: The new taxon is based on composite skull and mandible including premaxilla, maxilla, jugal, quadrate, braincases, predentary, dentaries, surangular, and maxillary and dentary teeth.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.

View Article: PubMed Central - PubMed

Affiliation: Institute of Dinosaur Research, Fukui Prefectural University, 4-1-1 Kenjojima, Matsuoka, Eiheiji-Cho, Fukui, 910-1195, Japan.

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.

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Right dentary (NRRU3001-167) of Sirindhorna.In labial (A), lingual (B), and occulusal (C) views. Abbreviations: alv.tr, alveolar trough; c.pr, coronoid process; gr, groove; nv.f, neulovascular foramen; sym, symphysis; v.pr, ventral process. Scale bar equals 10 cm.
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pone.0145904.g010: Right dentary (NRRU3001-167) of Sirindhorna.In labial (A), lingual (B), and occulusal (C) views. Abbreviations: alv.tr, alveolar trough; c.pr, coronoid process; gr, groove; nv.f, neulovascular foramen; sym, symphysis; v.pr, ventral process. Scale bar equals 10 cm.

Mentions: Two dentaries have been unearthed from the site, one is a left dentary with well-preserved teeth in situ but the rostral part of the dentary is missing (Fig 9; NRRU3001-14); the other is a nearly complete right dentary which lacks observable teeth (Fig 10; NRRU3001-167). The following description is based on these two specimens. The dentary consists of a deep dentary ramus and a thumb-shape large coronoid process in lateral view (Figs 9A and 10A). The ventral edge of the dentary ramus is nearly straight and the ventral surface of the symphyseal region is visible (Fig 10A). The coronoid process is relatively robust and large. It is slightly expanded along its rostral and caudal margins with a pointed dorsal tip. The coronoid process is subvertical on both specimens (Figs 9A and 10A). The lateral surface of the dentary is nearly flat at the rostral part but shows convexity at the base of the coronoid process. In medial view (Fig 10B), a short diastema exists between the first alveolar trough and the predentary articulation [36]. The symphysis faces rostromedially at the rostral tip of the dentary. The thin alveolar parapet covers over more than half of the dorsoventral depth of each tooth family (Fig 9B). There are seven completely preserved and two broken neurovascular foramina recognizable on the medial side (Fig 9B). The foramina are linked by weak grooves, which probably marks the passage for the main blood vessel and sensory nerve trunk [35]. One functional and two replacement teeth are housed in each tooth family. However, the 2nd replacement tooth crown is rudiment with undeveloped enamel and can be seen through the neurovascular foramen (Fig 9B). There are twenty alveoli and five incomplete replacement teeth preserved in the right dentary (Fig 10B). The alveoli are simple grooves, but are shaped like the crown of a tooth at the base (Fig 10B). The dorsoventral depths of the alveoli decrease rostrally and caudally, and are greatest at the middle of the tooth row around 12th alveolus. The caudal end of the tooth row is positioned rostral to the apex of the coronoid process on both specimens. Ventral to the alveolar parapet, there is a deep and large groove called the Meckelian canal (Figs 7B and 8B). In dorsal view, the tooth row slightly curves medially at the base of the coronoid process (Figs 9C and 10C). Although the right dentary preserves no functional teeth, the row of alveoli, which corresponds to the tooth row, is also slightly arched medially (Fig 10C). The cheek recess (or buccal shelf) between the coronoid process and the caudal-most alveolar trough is present (Figs 9B and 10C).


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

Shibata M, Jintasakul P, Azuma Y, You HL - PLoS ONE (2015)

Right dentary (NRRU3001-167) of Sirindhorna.In labial (A), lingual (B), and occulusal (C) views. Abbreviations: alv.tr, alveolar trough; c.pr, coronoid process; gr, groove; nv.f, neulovascular foramen; sym, symphysis; v.pr, ventral process. Scale bar equals 10 cm.
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4696827&req=5

pone.0145904.g010: Right dentary (NRRU3001-167) of Sirindhorna.In labial (A), lingual (B), and occulusal (C) views. Abbreviations: alv.tr, alveolar trough; c.pr, coronoid process; gr, groove; nv.f, neulovascular foramen; sym, symphysis; v.pr, ventral process. Scale bar equals 10 cm.
Mentions: Two dentaries have been unearthed from the site, one is a left dentary with well-preserved teeth in situ but the rostral part of the dentary is missing (Fig 9; NRRU3001-14); the other is a nearly complete right dentary which lacks observable teeth (Fig 10; NRRU3001-167). The following description is based on these two specimens. The dentary consists of a deep dentary ramus and a thumb-shape large coronoid process in lateral view (Figs 9A and 10A). The ventral edge of the dentary ramus is nearly straight and the ventral surface of the symphyseal region is visible (Fig 10A). The coronoid process is relatively robust and large. It is slightly expanded along its rostral and caudal margins with a pointed dorsal tip. The coronoid process is subvertical on both specimens (Figs 9A and 10A). The lateral surface of the dentary is nearly flat at the rostral part but shows convexity at the base of the coronoid process. In medial view (Fig 10B), a short diastema exists between the first alveolar trough and the predentary articulation [36]. The symphysis faces rostromedially at the rostral tip of the dentary. The thin alveolar parapet covers over more than half of the dorsoventral depth of each tooth family (Fig 9B). There are seven completely preserved and two broken neurovascular foramina recognizable on the medial side (Fig 9B). The foramina are linked by weak grooves, which probably marks the passage for the main blood vessel and sensory nerve trunk [35]. One functional and two replacement teeth are housed in each tooth family. However, the 2nd replacement tooth crown is rudiment with undeveloped enamel and can be seen through the neurovascular foramen (Fig 9B). There are twenty alveoli and five incomplete replacement teeth preserved in the right dentary (Fig 10B). The alveoli are simple grooves, but are shaped like the crown of a tooth at the base (Fig 10B). The dorsoventral depths of the alveoli decrease rostrally and caudally, and are greatest at the middle of the tooth row around 12th alveolus. The caudal end of the tooth row is positioned rostral to the apex of the coronoid process on both specimens. Ventral to the alveolar parapet, there is a deep and large groove called the Meckelian canal (Figs 7B and 8B). In dorsal view, the tooth row slightly curves medially at the base of the coronoid process (Figs 9C and 10C). Although the right dentary preserves no functional teeth, the row of alveoli, which corresponds to the tooth row, is also slightly arched medially (Fig 10C). The cheek recess (or buccal shelf) between the coronoid process and the caudal-most alveolar trough is present (Figs 9B and 10C).

Bottom Line: The new taxon is based on composite skull and mandible including premaxilla, maxilla, jugal, quadrate, braincases, predentary, dentaries, surangular, and maxillary and dentary teeth.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.

View Article: PubMed Central - PubMed

Affiliation: Institute of Dinosaur Research, Fukui Prefectural University, 4-1-1 Kenjojima, Matsuoka, Eiheiji-Cho, Fukui, 910-1195, Japan.

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.

Show MeSH
Related in: MedlinePlus