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Juvenile specimen of Yunnanosaurus from Early Jurassic of China
From: Ben Creisler
A new online paper:
Toru Sekiya, Xingsheng Jin, Wenjie Zheng, Masateru Shibata & Yoichi Azuma (2013)
A new juvenile specimen of Yunnanosaurus robustus (Dinosauria:
Sauropodomorpha) from Early to Middle Jurassic of Chuxiong Autonomous
Prefecture, Yunnan Province, China.
Historical Biology (advance online publication)
An almost complete skeleton with partial cranial material (ZMNH-M8739)
is recovered from the Early or Middle Jurassic of southwest China.
ZMNH-M8739 is identified as a juvenile individual of basal
sauropodomorph dinosaur, Yunnanosaurus robustus Young, 1951. The
revised diagnoses are as follows: absence of anteroposterior expansion
on the medial end of astragalus and dorsoventrally compressed medium
shaft of the metatarsal IV. Unfused neural arch and finely grooved
long bone surface texture indicate that this individual is in the
immature growth stage. ZMNH-M8739 possesses the tooth–tooth wear facet
on its mesial maxillary and dentary teeth. However, the distal
maxillary teeth have coarse serrations. Such a characteristic
dentition could represent a unique feeding mechanism of this animal.
Finally, ZMNH-M8739 constitutes a monophyletic group with Y. robustus
(holotype), and Y. huangi is nesting this clade in the phylogenetic
tree of the present analysis. Comparison of juvenile and adult
specimen reveals distinctive growth changes of Y. robustus. This clade
is positioned in an unnamed clade at a sister taxon of Sauropoda.
Finally, some members of the so-called prosauropod dinosaurs
constitute a monophyletic group in the present result.