Garganornis (meaning "Gargano bird") is an extinct genus of enormous flightless anatid waterfowl from the Late Miocene of Gargano, Italy. The genus contains one species, G. ballmanni, named by Meijer in 2014. Its enormous size is thought to have been an adaptation to living in exposed, open areas with no terrestrial predators, and as a deterrent to the indigenous aerial predators like the eagle Garganoaetus and the giant barn owl Tyto gigantea.

The tibiotarsus of Garganornis is approximately 30% larger than that of the living mute swan in circumference. Based on comparisons with the latter, it has been estimated that Garganornis had a weight in the range of 15–22 kilograms (33–49 lb), larger than any living anatid. This suggests that it was likely flightless.

The preserved carpometacarpi from the wings had quite a short and robust shaft, much shorter than any of the living large-bodied anseriforms that are capable of flight. The carpometacarpus was also peculiarly flattened on its top end; and the trochlea carpalis (a bony articular process that drives wing extension and flexion) is reduced and weak in shape, limiting wrist movement—both likely adaptations to a flightless life.

In some specimens of Garganornis, there is a small bony knob on the top of the carpometacarpus that is similar to that of swans, geese, ducks, and other anseriforms; this was likely used for fighting, as in other members of the group.

Likewise short and robust was the tarsometatarsus of the foot. The processes known as the trochlea metatarsi II and IV, on the bottom portion of the tarsometatarsus, are more equal in length than most other anseriforms, with the exception of the Cape Barren goose, screamers, and the giant, extinct Cygnus falconeri. The phalanx bones of the toes are also relatively robust, and similar to other giant anseriforms; however, the impressions of ligaments on the bones are weaker and less defined.

The first remains of Garganornis were discovered from the Posticchia 5 fissure filling near the town of Apricena in Gargano, Italy. These deposits are part of the Miocene Mikrotia faunal assemblage (named after an abundant murid rodent), which has been dated to 6–5.5 Ma in age. The holotype consists of a single partial left tibiotarsus, catalogued as RGM 443307, which was described by Meijer in 2014.

Additional material was later described from Gargano by Pavia et al. in 2016, consisting of partial carpometacarpi (DSTF-GA 49, NMA 504/1801), a single damaged tibiotarsus (DSTF-GA 77), partial tarsometatarsi (RGM 425554, RGM 425943), and various phalanx bones from the foot (MGPT-PU 135356, RGM 261535, RGM 261945). Additionally, some geologically earlier but morphologically comparable material was described from the Scontrone locality, which is close to the town of Scontrone and has been dated to 9 Ma in age. This material consists of an almost complete tarsometatarsus, SCT 23; although it is temporally separated from the other material, the morphology and unusually large size of the bone suggests that it pertains to Garganornis.

The genus name Garganornis is derived from the general area of Gargano, in which the holotype fossils were discovered; the Greek suffix ornis means "bird". The species name honors Peter Ballmann, who first described the birds of the Gargano region.