Longipterygidae

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 Enantiornithes. Where most Enantiornithes 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 longipteryigids lived primarily in trees. Because their long jaws tipped with large, often curved teeth are usually considered an adaptation for catching and eating fish, it is likely that they were similar in ecology to modern Kingfishers.[3] Other interpretations of their habitus include mud-probing and the probing for insects behind tree bark.[2]

The Longipterygidae was first coined as a family of enantiornithean birds by Zhang and colleagues in 2001. They included only the first known species, Longipteryx chaoyangensis, and placed the family in its own order, Longipterygiformes.[4] While Longipterygiformes has never been formally defined, Longipterygidae was given a phylogenetic definition by O'Connor and colleagues in 2009. They defined the clade to include Longipteryx, Longisrostravis, their most recent common ancestor, and all of its descendants.[5]

The cladogram below was found in the phylogenetic analysis of O'Connor, Gao and Chiappe (2010a).[6]

Subsequently, the following cladogram was found in the phylogenetic analysis of Li et al (2012):[7]