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| Gretcheniao sinensis
Chiappe, Qingjin, Serrano, Sigurdsen, Min, Bell & Di, 2019
DOI: 10.7717/peerj.7846
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Abstract
During the last decade, several Bohaiornis-like enantiornithine species—and numerous specimens—have been recognized from the celebrated Jehol Biota of northwestern China. In this paper, we describe the anatomy of another “bohaiornithid” species from the 125 million-year-old Yixian Formation of Liaoning Province, China. The new taxon differs from previously recognized “bohaiornithids” on a number of characters from the forelimb and shoulder girdle. We also provide a new phylogenetic framework for enantiornithine birds, which questions the monophyly of the previously recognized bohaiornithid clade and highlights ongoing challenges for resolving enantiornithine interrelationships. Additionally, we offer the first assessment of the flight properties of Bohaiornis-like enantiornithines. Our results indicate that while “bohaiornithids” were morphologically suited for flying through continuous flapping, they would have been unable to sustain prolonged flights. Such findings expand the flight strategies previously known for enantiornithines and other early birds.
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| Figure 1: Photo of the holotype of Gretcheniao sinensis (BMNHC Ph 829). |
Systematic Paleontology
Aves Linnaeus, 1758
Pygostylia Chiappe, 2002
Ornithothoraces Chiappe, 1995
Enantiornithes Walker, 1981
Gretcheniao sinensis gen. et sp. nov.
Holotype. BMNH Ph 829 (Beijing Museum of Natural History, Beijing, China) (Fig. 1; Table 1). Nearly complete skeleton, largely exposed in ventral view, and contained in a single slab. Faint remnants of plumage are preserved as carbonized material, primarily around the neck and projecting from the distal portion of the left forelimb. A resin cast of the specimen is deposited in the collection of the Dinosaur Institute of the Natural History Museum of Los Angeles County under the number LACM 7917/156630.
Etymology. Gretcheniao in recognition of Mrs. Gretchen Augustyn and her support to the Dinosaur Institute of the Natural History Museum of Los Angeles County, and the Chinese character (niăo), meaning “bird”; sinensis from “sino,” a term generally used in reference to China.
Geographic and Stratigraphic Provenance. BMNH Ph 829 (Fig. 1) was recovered from strata belonging to the Early Cretaceous Yixian Formation in Jianchang County, near Huludao City in Western Liaoning, China. The fossiliferous beds of the Yixian Formation have been dated at approximately 125 million-year-old (Swisher et al., 2002; He et al., 2004, 2006), corresponding to the Barremian Epoch of the Cretaceous.
Differential Diagnosis. A medium-sized enantiornithine bird sharing the following traits with other “bohaiornithids”: robust rostrum with large subconical teeth that are gently recurved, caudolaterally directed lateral trabeculae of the sternum, and strongly curved and elongated pedal claws. The new species is distinguishable from other Bohaiornis-like enantiornithines in having a unique combination of characters including: humeral bicipital area scared by a large cranioventrally facing fossa; slightly tapered omal ends of the furcular rami; ventral tubercle at the convergence of the furcular rami; slender coracoid with a sternal margin that is slightly more than 1/3 the length of the bone and a straight lateral margin; significantly elongated carpometacarpus; and metacarpal II carrying a protuberance on its dorsal surface.
Conclusion:
BMNH Ph 829 adds diversity to the overall anatomy of Bohaiornis-like enantiornithines (“bohaiornithids”) by providing morphological details previously unknown for these birds. The unique combination of skeletal traits of BMNH Ph 829 supports the recognition of a new species, Gretcheniao sinensis, which appears to represent an early divergence among these birds. Nonetheless, our extensive cladistic analyses show that despite the discovery of many well-preserved enantiornithines from the Jehol Biota (Chiappe & Meng, 2016), the interrelationships of these birds remain contentious. Our analyses do not recover a monophyletic clade of the six species that have been previously considered as “bohaiornithids”—only a subset of these are clustered in a monophyletic group. Further studies are needed to test whether these previously identified “bohaiornithids” constitute an evolutionary grade, sharing an overall morphology (largely symplesiomorphic characters) but lacking a single common ancestry. The degree to which these “bohaiornithids” may have shared a similar ecology needs to be further explored considering that some of them (e.g., Fortunguavis xiaotaizicus) have been interpreted as highly specialized (i.e., scansorial) (Wang, O’Connor & Zhou, 2014).
Our study also provides the first assessment of the flight properties of “bohaiornithid” enantiornithines. Key flight parameters inferred for these birds suggest ineffectiveness for performing intermittent flight (either flap-gliding or bounding) that was inferred for other enantiornithines (Liu et al., 2017, 2019; Serrano et al., 2017, 2018). Instead, these parameters indicate that Gretcheniao sinensis and other “bohaiornithids” were morphologically suited for flying through continuous flapping, although not able to perform prolonged flights. Our aerodynamic results thus expand the previously known aerial repertoire of the Cretaceous enantiornithines.
Luis M. Chiappe, Meng Qingjin, Francisco Serrano, Trond Sigurdsen, Wang Min, Alyssa Bell and Liu Di. 2019. New Bohaiornis-like Bird from the Early Cretaceous of China: Enantiornithine Interrelationships and Flight Performance. PeerJ. 7:e7846. DOI: 10.7717/peerj.7846
