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.

[2] 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.

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.

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.

[2] 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".

[1] However, given that gastornithids and other Paleogene fauna do not appear to have survived in - or even reached - this region, it is more likely that these shared traits are convergent adaptations to gigantic body sizes.

Other rodents include the giant dormice Stertomys laticrestatus, S. daunius, and S. lyrifer, along with the smaller species S. deguili, S. simplex, and S. daamsi;[11][10][12] and the hamsters Hattomys gargantua, H. nazarii,[11][10][12] Neocricetodon sp., and Apocricetus sp.

[11] The gymnures (hairy hedgehogs) Deinogalerix freudenthalli, D. minor, D. intermedius, D. brevirostris, D. koenigswaldi, and D. masinii were also giant,[11][12] while their smaller relative Apulogalerix cf.