[3] Longipterygids are characterized by an extremely long, toothed snout (making up over 60% of the total skull length), in which the teeth are restricted to the tips of the jaws.

Their pygostyles, the series of fused vertebrae in the tail, were unusually large, and longer than the foot bones.

[4] Previous interpretations of their diet are either piscivorous or insectivorous,[4][5][6] but direct evidence from the gut content showed that Longipteryx was frugivorous, as indicated by the discovery of complete gymnosperm seeds and a lack of gastroliths within two specimens, STM8–86 and STM8–112.

[7] The authors of the 2024 study who reported direct evidence of frugivory in Longipteryx suggested that researchers should be cautious when predicting the diets in extinct taxa based on "untested morphological proxies".

They defined the clade to include Longipteryx, Longisrostravis, their most recent common ancestor, and all of its descendants.