The smallest known non-avian theropod dinosaur

Abstract

Non-avian dinosaurs are mostly medium to large-sized animals, and to date all known mature specimens are larger than the most primitive bird, Archaeopteryx1. Here we report on a new dromaeosaurid dinosaur, Microraptor zhaoianus gen. et sp. nov., from the Early Cretaceous Jiufotang Formation of Liaoning, China2. This is the first mature non-avian dinosaur to be found that is smaller than Archaeopteryx1, and it eliminates the size disparity between the earliest birds and their closest non-avian theropod relatives. The more bird-like teeth, the Rahonavis -like ischium and the small number of caudal vertebrae of Microraptor are unique among dromaeosaurids and improve our understanding of the morphological transition to birds. The nearly completely articulated foot shows features, such as distally positioned digit I, slender and recurved pedal claws, and elongated penultimate phalanges, that are comparable to those of arboreal birds3,4,5,6. The discovery of these in non-avian theropods provides new insights for studying the palaeoecology of some bird-like theropod dinosaurs.

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Figure 1: Main slab (V 12330, holotype) containing M. zhaoianus.
Figure 2: Outline of skeleton and identification of the skull with lower jaws and an anterior and posterior dentary tooth of M. zhaoianus (V 12330).
Figure 3: Identification of pelvic girdle, right forelimb and pes of M. zhaoianus (V 12330).
Figure 4: Integument of M. zhaoianus (V 12330).
Figure 5: Phylogenetic relationships of M. zhaoianus.

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Acknowledgements

We thank D. Unwin, L. Chiappe, X.-C. Wu, J. Clark and L. Witmer for comments; M.-M. Chang and Y.-Q. Wang for assistance during the course of the work; H.-J. Wang for preparing the specimen; R.-S. Li for making the drawings; and J. Zhang and H.-L. You for taking the photographs. This work was supported by the Special Funds for Major State Basic Research Projects of China, and research grants from the National Geographic Society of the United States, Chinese Natural Science Foundation, and the Chinese Academy of Sciences.

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Correspondence to Xing Xu.

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Xu, X., Zhou, Z. & Wang, X. The smallest known non-avian theropod dinosaur. Nature 408, 705–708 (2000). https://doi.org/10.1038/35047056

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