Monoenantiornis sihedangia was named by Hu and O'Connor (2017) [A medium to large-sized enantiornithine bird characterized by the following unique combination of morphological features: small teeth with unrecurved and pointed apices; premaxillary teeth with grooves on the lingual side; sternum with a narrowly vaulted rostral margin; lateral trabeculae directed caudolaterally and terminating cranial to the distal end of the xiphoid process; furcular articular surface of scapula large and triangle-shaped; distal half of the lateral margin of the coracoid corpus strongly convex; extension of the minor metacarpal beyond the distal end of the major metacarpal more than 15% the length of the latter (autapomorphy); single and low cnemial crest on tibia present along the proximal 30% of the cranial surface; foot with extremely robust digit II and delicate digit IV.]. Its type specimen is IVPP V20289, a partial skeleton (a nearly complete and articulated subadult individual preserved in a single slab in ventral view, only missing some of the vertebrae, the ilia and the ischia), and it is a 3D body fossil. Its type locality is Sihedang, Lingyuan, which is in an Aptian lacustrine mudstone/shale in the Jiufotang Formation of China. It is the type species of Monoenantiornis.