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Kompsornis (meaning "elegant bird") is an extinct genus of avialan that lived during the Early Cretaceous Cretaceous period of China. The Type species and only known species is Kompsornis longicaudus; the specific name means "long-tailed". It is known from only a single fossil specimen from the Jiufotang Formation. Kompsornis was closely related to the well-known Jeholornis, another long-tailed avialan from China, but differs from it in features of its skeleton, particularly the fusion and growth rate of its bones. Like other jeholornithiforms, Kompsornis was a long-tailed avialan with long and possessed little or no teeth, with none identified in the single specimen of Kompsornis.
A phylogenetic analysis supported this conclusion, which recovered Kompsornis as a jeholornithiform most closely related to Jeholornis prima and J. curvipes ( Jeholornis 'sensu stricto'), and more derived than Shenzhouraptor, J. palmapenis and Jixiangornis:
Kompsornis is distinguished from other jeholornithiform species by traits such as a more posteriorly directed pubis, especially elongated caudal vertebrae in the tail, extreme tail length, longer forelimbs, and features of the sternum and coracoid in the shoulder. The hip and sternum are also more extensively fused than in other jeholornithiforms, despite its immaturity, and the skeleton overall has more bird-like growth patterns than in other sampled jeholornithiforms.
The sternum is completely fused, and possesses a well-developed keel and a robust xiphoid process, suggesting that Kompsornis was a powerful flier.
Palaeobiology
The growth rate of Kompsornis was sampled from a cross-section of a rib bone and compared to those of Jeholornis sp. The specimen was determined to be at least four years old and approaching maturity, but was not yet fully grown. Kompsornis possessed a different growth strategy to Jeholornis, particularly in the fusion of the sternum and hips prior to skeletal maturity, which often remain unfused even in larger and older specimens of Jeholornis. Such differences in growth patterns may be evidence that jeholornithiforms evolved distinct growth strategies to adopt different ecologies in the same environment.
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