The clade Avialae is defined as containing all living Birds, plus anything more closely related to them than either Deinonychus or Troodon. This group appeared in the Middle-to-Late Jurassic, but pre-Cretaceous fossils are rare and limited to a small number of locations, making the early history of the Avialans somewhat unclear. The oldest known Avialan fossils probably come from the Yanliao Biota in northeast China, where they first appear about 166 million years ago, with slightly younger specimens, including Archaeopterix, coming from the Solnhofen Limestones of Germany, although these have not been precisely dated. Following these two fossil lagerstatten there is a gap of about 30 million years before further Avialan fossils appear in the Early Cretaceous Huajiying Formation of Hainan Island, South China. Clearly, understanding the nature of these Jurassic stem-Birds is a key to understanding the global Avialan diversification at the beginning of the Cretaceous.
In a paper published in the journal Nature on 6 September 2023, Liming Xu of the Fujian Institute of Geological Survey, Min Wang of the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences, Runsheng Chen, also of the Fujian Institute of Geological Survey, Liping Dong, also of the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences, Min Lin, again of the Fujian Institute of Geological Survey, Xing Xu, again of the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences, and of the Centre for Vertebrate Evolutionary Biology at Yunnan University, and of the Paleontological Museum of Liaoning at Shenyang Normal University, Jianrong Tang, again of the Fujian Institute of Geological Survey, Hailu You, again of the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences, Guowu Zhou, Linchang Wang, Wenxing He, and Yujuan Li, all of the Fujian Institute of Geological Survey, and Chi Zhang and Zhonghe Zhou, again of the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences, describe a new species of Avialan Theropod from an outcrop the Late Jurassic (149.9–150.2 million years old) Nanyuan Formation near Yangyuan Village in Zhenghe Country in Fujian Province, China, the first Avialan to be described from this recently discovered locality, which has to date yielded more than 100 well-preserved Vertebrate fossils, and shows signs of becoming a significant Late Jurassic fossil lagerstatten.
The new species is descried from a single partial skeleton, preserved on a slab and counter slab. It is given the name Fujianvenator prodigiosus, where 'Fujianvenator' means 'Fujian hunter', and 'prodigiosus' is intended to mean 'bizarre', in reference to the unusual nature of the specimen. The single known specimen is not considered to be skeletally mature, on the basis of its unfused metacarpals and tibiotarsus, although it does have a fused astragalus and calcaneum and an ossified sternum, implying that it was close to maturity when it died.
Fujianvenator prodigiosus has a mosaic combination of Theropod, Avialan, and unique features, including vertebrae increase in length increases further back on the spine, with the fifth vertebra twice as long as the first, something seen in Cretaceous Avialans such as Jeholornis, but not Jurassic forms such as Archaeopterix, a scapula significantly shorter than the humerus, something not found in other Theropods or early Avialans, a humerus significantly longer than the scapula, something seen in among Theropods only in Cretaceous Avialans and the Scansoriopterygids (a group of Jurassic Maniraptors believed to have evolved flight independently of the Birds), an ossified sternum, again seen in Cretaceous Avialans and Scansoriopterygids, a small deltopectoral crest on the humerus, seen in other Jurassic Avialans, an ulna shorter than the humerus, typical of non-Avialan Theropods, a straight ulna, seen in some early Avialans, but absent in others, and in most closely related Theropods.
A phylogenetic analysis recovered Fujianvenator prodigiosus as a member of the e Anchiornithidae, the sister group to all other Avialans (including Archaeopterix and all Cretaceous Avialans), and which until has contained only species from the Yanliao Biota. Fujianvenator prodigiosus is ten million years younger than the Yanliao Biota Avialans, and the most southerly Jurassic Avialan discovered to date, and therefore represents a significant increase to our knowledge of Jurassic Avialans. It the proportions of its manual phalanges (hands) are similar to those of Archaeopterix, while its pevis appears closer to those of Anchiornis and Troodontids, while its feet show a range of mixture of features seen in Archaeopteryx, Anchiornis, Troodontids, and Dromaeosaurids.
The evolution of early Avialans has long thought to have been driven by adaptation for flight, however, Fujianvenator prodigiosus does not appear particularly suited to flying, and a morphometric analysis suggests that it was probably better suited to a terrestrial lifestyle. Its hands appear to have been quite flexible, which would be good for grasping prey, but would lessen the ability to support weight on wing feathers during flight, while its hindlimbs were long and its feet well adapted for running.
In fact, the morphometric analysis suggested that the hindlimbs of Fujianvenator prodigiosus were uniquely well suited to running, compared to other Mesozoic Theropods, although Xu et al. note that long limbs in a modern Bird can be an indicator of a wading lifestyle rather than a running one, and the preservation of the lower limbs of the specimen is not sufficiently good to eliminate either possibility. The Nanyuan Formation, from which the specimen was obtained, comprises a mixture of mudstones and shales, and many of the fossils recovered from it are of species aquatic or semi-aquatic in nature, implying a wetland environment, quite different from the environments recorded by the Yanliao Biota and the Solnhofen Limestones, increasing our knowledge of the ecosystems in which the earliest Avialans lived.
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