Stenornis is an extinct genus of Plotopteridae, a family of large-sized, flightless seabirds native from the North Pacific during the Paleogene and the earliest Neogene.

The remains of Stenornis have been found in Oligocene rocks of the Jinnobaru Formation on Hikoshima and the Ashiya Group on Ainoshima, Japan.

Given the paucity of its remains, Stenornis is mainly differentiated from its relatives by osteological details of its coracoid, including the presence of a sulcus elongated craniocaudally on the ventral surface of the shaft, a processus lateralis located toward the cranial portion of the shaft, and a face where the coracoid articulates with the clavicle broader than all other plotopterids and bean-shaped.

Despite being similarly sized with its relative Copepteryx, found in the same deposits, the coracoid was slightly smaller, although much larger than that of Tonsala,[1] more gracile, with a narrower sternal end and a broader and proximally situated lateral process.

Fossil remains of sharks, pelagornithid seabirds, and early whales like the eomysticetid Yamatocetus have also been recovered in Oligocene sediments belonging to the group.