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| Imparavis attenboroughi Wang, Clark, O'Connor, Zhang, Wang, Zheng & Zhou, 2024 Artwork: Ville Sinkkonen. |
Abstract
Among Mesozoic birds, enantiornithines exhibit great morphological variation, which likely reflects their species diversity, range, and overall success throughout the Cretaceous. The majority of enantiornithines come from the Lower Cretaceous Jehol deposits (130–120 Ma) in northeastern China. In contrast to living birds, most enantiornithines were fully toothed. However, the rostral lengths, appendicular proportions, and pedal morphologies of extant birds can still inform on possible diet, flight mode, and ecology. Both partial (e.g., Longipterygidae) and complete tooth loss (e.g., Yuornis, Gobipteryx) are observed among enantiornithines, with edentulous rostra previously restricted to Upper Cretaceous taxa. Here, we describe the first edentulous enantiornithine from the Lower Cretaceous, Imparavis attenboroughi gen. et sp. nov., indicating a toothless beak evolved in this group 48 Ma earlier than previously recognized. Additionally, we reinterpret Chiappeavis as edentulous which together with the discovery of Imparavis indicates the complete loss of teeth in enantiornithines was not uncommon although still less frequent than observed in ornithuromorphs. The absence of gastroliths in all known enantiornithines suggests that the loss of teeth evolved under different pressures in these two ornithothoracine clades. Differences in rostral occlusion between Imparavis and Chiappeavis suggest they utilized different foraging strategies and possibly diet. Appendicular morphology in Imparavis suggest the capacity for relatively high wing beat frequency and powerful take-off capabilities. Together with the morphology of the hindlimb, we suggest Imparavis was primarily a terrestrial forager that could utilize sudden bursts of flight to escape into arboreal settings as a prey evasion strategy.
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| Illustration showing the fossil skeleton of Imparavis attenboroughi, alongside a reconstruction of the bird in life. Artwork: Ville Sinkkonen. |
Systematic paleontology
Aves Linnaeus, 1758
Pygostylia Chiappe, 2002
Ornithothoraces Chiappe, 1995
Enantiornithes Walker, 1981
Imparavis attenboroughi gen. et sp. nov.
Locality and horizon. Collected near the village of Toudaoyingzi, Jianchang County, Liaoning Province, PR China; Lower Cretaceous Jiufotang Formation, 120 Ma (Lower Aptian) (He et al., 2004; Pan et al., 2013).
Conclusions:
Imparavis attenboroughi represents the first known edentulous enantiornithine from the Lower Cretaceous. The discovery of this taxon contributes to the multiple independent evolutionary occurrences of complete tooth loss among Mesozoic birds. The loss of teeth in enantiornithines may be linked to shifts in feeding behavior; however, as yet there is no evidence that this shift was driven by herbivory as is suggested for ornithuromorphs and non-avian dinosaurs. Rostral occlusion in Imparavis ....
Xiaoli Wang, Alexander D. Clark, Jingmai K. O'Connor, Xiangyu Zhang, Xing Wang, Xiaoting Zheng and Zhonghe Zhou. 2024. First Edentulous Enantiornithine (Aves: Ornithothoraces) from the Lower Cretaceous Jehol Avifauna. Cretaceous Research. 159, 105867. DOI: 10.1016/j.cretres.2024.105867