Tuesday, October 24, 2017

[PaleoOrnithology • 2017] Junornis houi • Flight Aerodynamics in Enantiornithines: Information from A New Chinese Early Cretaceous Bird

Junornis houi 
Liu, Chiappe, Serrano, Habib, Zhang and Meng, 2017


We describe an exquisitely preserved new avian fossil (BMNHC-PH-919) from the Lower Cretaceous Yixian Formation of eastern Inner Mongolia, China. Although morphologically similar to Cathayornithidae and other small-sized enantiornithines from China’s Jehol Biota, many morphological features indicate that it represents a new species, here named Junornis houi. The new fossil displays most of its plumage including a pair of elongated, rachis-dominated tail feathers similarly present in a variety of other enantiornithines. BMNHC-PH-919 represents the first record of a Jehol enantiornithine from Inner Mongolia, thus extending the known distribution of these birds into the eastern portion of this region. Furthermore, its well-preserved skeleton and wing outline provide insight into the aerodynamic performance of enantiornithines, suggesting that these birds had evolved bounding flight—a flight mode common to passeriforms and other small living birds—as early as 125 million years ago.


Systematic Paleontology

Aves Linnaeus, 1758  
Pygostylia Chiappe, 2001  
Ornithothoraces Chiappe, 1995  

Enantiornithes Walker, 1981 

Junornis houi gen. et sp. nov.

Fig 1. Slab (BMNHC-PH 919a) (A) and counterslab (BMNHC-PH 919b) (B) of Junornis houi.

Holotype: A nearly complete and articulated skeleton (BMNHC-PH 919; Beijing Museum of Natural History) contained in two slabs (a, b). While the skeleton is preserved as voids of the bony elements, it is surrounded by feather impressions defining the surface of its wings and body outline (Fig 1).

Horizon and locality: Yixian Formation, Early Cretaceous (~ 126±4 mya); Liutiaogou Village, Daming Town, Ningchen County, Inner Mongolia Autonomous Region, China.

Etymology: The generic name Jun is derived from a Chinese character () meaning beautiful; ornis is Greek for bird. The species name, houi honors Dr. Hou Lianhai and his important contributions to Chinese paleornithology.

Diagnosis: A small Cathayornis-like bird distinguishable from other similar enantiornithines by the following combination of characters: rounded craniolateral corner of sternum (more angular in Cathayornis yandica and Houornis caudatus); distinct trough excavating ventral surface of mediocranial portion of sternum; triangular process at base of sternal lateral trabecula (absent in H. caudatus and E. walkeri); sternal lateral trabecula broad (much wider than in C. yandica, E. walkeri, and H. caudatus) and laterally deflected (straight in C. yandica and E. walkeri); sternal intermediate trabecula nearly level with mid-shaft of lateral trabecula (significantly shorter in C. yandica, H. caudatus and E. walkeri); sternal xiphoid process level with lateral trabeculae (trabeculae project further caudal in H. cautus and C. yandica); costal processes of last two penultimate synsacral vertebrae three times wider than same process of last synsacral vertebra; and very broad pelvis.

The discovery of Junornis houi, the first published record of a Jehol enantiornithine from Inner Mongolia Autonomous Region, extends the geographic distribution of these early birds into the eastern portion of this region. The well-preserved wings and overall plumage of BMNHC-PH 919 adds significant information to the poor evidence of wing shape in Enantiornithes. Multiple regressions of skeletal elements and remiges allow estimation of key aerodynamic parameters (aspect ratio and wing loading) for this new enantiornithine. The small size, low aspect ratio, and low wing loading of BMNHC-PH 919 indicate that Junornis houi and other similar enantiornithines could have used bounding as their typical flight mode, especially at high speeds. The general morphology of BMNHC-PH 919 thus supports previous interpretations indicating that most avian flight modes have very ancient origins; bounding flight might have evolved among enantiornithines more than 125 million years ago.

 Di Liu, Luis M. Chiappe, Francisco Serrano, Michael Habib, Yuguang Zhang and Qinjing Meng. 2017. Flight Aerodynamics in Enantiornithines: Information from A New Chinese Early Cretaceous Bird. PLoS ONE. 12(10): e0184637.  DOI: 10.1371/journal.pone.0184637


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