Longipterygidae

Description

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. The snouts were straight but slightly concave at a point behind the nostrils, and the bones of the snout tip were solid. Their pygostyles, the series of fused vertebrae in the tail, were unusually large, and longer than the foot bones. The feet of longipterygids were also specialized relative to other enantiornitheans. Where most enantiornitheans had a long middle toe with a "knuckle" (trochlea) that extended beyond the outer two, the toes of longipterygids were even in length, and attached to the rest of the foot at the same level. This configuration is also seen in some groups of modern birds and is usually considered an adaptation for advanced perching ability. It is likely that longipterygids lived primarily in trees. Previous interpretations of their diet are either piscivorous or insectivorous, 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. 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".