An oviraptorid skeleton from the late Cretaceous of Ukhaa Tolgod, Mongolia, preserved in an avianlike brooding position over an oviraptorid nest. American Museum novitates ; no. 3265

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New York, NY : American Museum of Natural History
"The articulated postcranial skeleton of an oviraptorid dinosaur (Theropoda, Coelurosauria) from the late Cretaceous Djadokhta Formation of Ukhaa Tolgod, Mongolia, is preserved overlying a nest. The eggs are similar in size, shape, and ornamentation to another egg from this locality in which an oviraptorid embryo is preserved, suggesting that the nest is of the same species as the adult skeleton overlying it and was parented by the adult. The lack of a skull precludes specific identification, but in several features the specimen is more similar to Oviraptor than to other oviraptorids. The ventral part of the thorax is exceptionally well preserved and provides evidence for other avian features that were previously unreported in oviraptorids, including the articulation of the first three thoracic ribs with the costal margin of the sternum and the presence of a single, ossified ventral segment in each rib as well as ossified uncinate processes associated with the thoracic ribs. Remnants of keratinous sheaths are preserved with four of the manal claws, and the bony and keratinous claws were as strongly curved as the manal claws of Archaeopteryx and the pedal claws of modern climbing birds. The skeleton is positioned over the center of the nest, with its limbs arranged symmetrically on either side and its arms spread out around the nest perimeter. This is one of four known oviraptorid skeletons preserved on nests of this type of egg, comprising 23.5% of the 17 oviraptorid skeletons collected from the Djadokhta Formation before 1996. The lack of disturbance to the nest and skeleton indicate that the specimen is preserved in the position in which the adult died. Its posture is the same as that commonly taken only by birds among tetrapods that brood their nest, and its close proximity to the eggs indicates that the nest was not covered, indicating that the behavior of sitting on open nests in this posture evolved before the most recent common ancestor of modern birds"--P. [1]-2.
36 p. : ill. (1 col.) ; 26 cm.
Includes bibliographical references (p. 31-35).