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.[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".[7]
Classification
The Longipterygidae was first coined as a family of enantiornitheans by Zhang and colleagues in 2001. They included only the first known species, Longipteryx chaoyangensis, and placed the family in its own order, Longipterygiformes.[8] 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.[9]
The cladogram below was found in the phylogenetic analysis of O'Connor, Gao and Chiappe (2010a).[10]
^Hartman, Scott; Mortimer, Mickey; Wahl, William R.; Lomax, Dean R.; Lippincott, Jessica; Lovelace, David M. (2019). "A new paravian dinosaur from the Late Jurassic of North America supports a late acquisition of avian flight". PeerJ. 7: e7247. doi:10.7717/peerj.7247. PMC 6626525. PMID 31333906.
^Morschhauser, E. M.; Varricchio, D.J.; Gao, C.; Liu, J.; Wang, Z.; Cheng, X. & Meng, Q. (2009). "Anatomy of the Early Cretaceous bird Rapaxavis pani, a new species from Liaoning Province, China". Journal of Vertebrate Paleontology. 29 (2): 545–554. doi:10.1671/039.029.0210. S2CID84643293.
^ abO’Connor, Jingmai K.; Zhou, Zhonghe; Zhang, Fucheng (28 February 2011). "A reappraisal of Boluochia zhengi (Aves: Enantiornithes) and a discussion of intraclade diversity in the Jehol avifauna, China". Journal of Systematic Palaeontology. 9 (1): 51–63. doi:10.1080/14772019.2010.512614. S2CID84817636.
^Zhou, Ya-Chun; Sullivan, Corwin; Zhou, Zhong-He; Zhang, Fu-Cheng (January 2021). "Evolution of tooth crown shape in Mesozoic birds, and its adaptive significance with respect to diet". Palaeoworld. 30 (4): 724–736. doi:10.1016/j.palwor.2020.12.008. S2CID234117375.
^ abO’Connor, J.; Clark, A.; Herrera, F.; Yang, X.; Wang, X.; Zheng, X.; Hu, H.; Zhou, Z. (2024). "Direct evidence of frugivory in the Mesozoic bird Longipteryx contradicts morphological proxies for diet". Current Biology. doi:10.1016/j.cub.2024.08.012.
^Zhang, Fucheng; Zhou, Zhonghe; Hou, Lianhai; Gu, Gang (1 June 2001). "Early diversification of birds: Evidence from a new opposite bird". Chinese Science Bulletin. 46 (11): 945–949. Bibcode:2001ChSBu..46..945Z. doi:10.1007/BF02900473. S2CID85215328.
^O'Connor, Jingmai K.; Wang, Xuri; Chiappe, Luis M.; Gao, Chunling; Meng, Qingjin; Cheng, Xiaodong; Liu, Jinyuan (12 March 2009). "Phylogenetic support for a specialized clade of Cretaceous enantiornithine birds with information from a new species". Journal of Vertebrate Paleontology. 29 (1): 188–204. doi:10.1080/02724634.2009.10010371. S2CID196607241.
