Insight into the evolution of avian flight from a new clade of Early Cretaceous ornithurines from China and the morphology of Yixianornis grabaui

“Twenty-two of the avialan taxa in the dataset are derived from the taxon-sampling regime of Clarke et al. (2006).”

“the flight feathers on the tail (retrices) in modern birds [70].”

“Dinosaurs are no exception [7,27,28] and it has recently been shown that basal nonavialan deinonychosaurs were actually miniaturized (,1 kg) and this size is primitive for Paraves (Deinonychosauria + Avialae) [22].”

“Previously, heterocoelous articulations were only known in taxa more closely related to extant birds than Enantiornithes (Clarke & Norell, 2002; Clarke et al. 2006).”

“First, using a taxonomic sample approximating that of Chiappe (2002), we assessed whether the proposed pattern of mosaic evolution would be recovered from summed apomorphies with a larger, partially overlapping character set (from Clarke et al., 2006).”

“Among archosaurs, co-ossification of the proximal tarsals only occurs in pterosaurs, Dromomeron, Lagerpeton (Sereno and Arcucci, 1994b), the ornithischian Heterodontosaurus (Santa Luca, 1980), and some theropods (including coelophysoids and avialans; Clarke et al., 2006; Irmis et al., 2007).”

“The ornithurine Yixianornis and its relatives (Clarke et al. 2006) were the first taxa to have a ‘ploughshare-shaped pygostyle’ correlated with the presence of retricial bulb and tail fanning (Baumel 1988; Gatesy and”

“STM9-5 is referable to Yanornis based on the following combination of features: carina approaching sternal anterior limit, scapula shorter than humerus, pubic symphysis relatively long, distal tarsals fused to metatarsals and metatarsals co-ossified proximally and distally, pedal digits relatively short and robust, an…”

“Yixianornis is described (Clarke et al. 2006) as having premaxillae fused in the front (rostrally) but not at the back.”

“…feature of paravians and is present in other dromaeosaurids (e.g., Ostrom, 1969; Norell and Makovicky, 1999; Burnham et al., 2000; Hwang et al., 2002; Norell et al., 2006), troodontids (e.g., Xu et al., 2002), and avialans (Clarke and Norell, 2002; Zhou and Zhang, 2002, 2003; Clarke et al., 2006).”

“preserved than the holotype of Chaoyangia (IVPP V9934), has appeared in several recent cladistic analyses (Clarke et al. 2006; Zhou et al. 2008a, 2009, 2010).”

“Recently, large phylogenetic analyses of avian relationships by Livezey and Zusi (2006, 2007) and analyses of basal avialans by Clarke et al. (2006) have used furcula synapomorphies to support avialan and, in some cases, more basal theropod relationships.”

“The sterna of Songlingornis, Yanornis, and Yixianornis all have one pair of free caudal trabeculae, lateral trabeculae that are robust with expanded distal ends, and a pair of caudal fenestrae laterally enclosed by a pair of medially curved strap-like bones inferred to be the intermediate trabeculae.”

“In contrast, Sapeornis , basal ornithuromorphs and a single possible enantiornithine, have a fan-shaped morphotype made up by a series of short rectrices, resembling that present in most living birds 2,34 .”

“Phylogenetic analysis indi cates that there are five major hierarchical radiations of Mesozoic birds—Avialae, Pygostylia, Enantiorni thes, Ornithuromorpha, and Ornithurae, which are successively closer to the crown group Aves (Clarke and Norell, 2002; Chiappe, 2002, 2007).”

“We combined the results of two recent large-scale phylogenetic studies (Clarke et al., 2006; Chiappe et al., 2007) to produce an informal supertree of Mesozoic birds that contains 27 terminal taxa.”

“…and Zhang, 2005), but in our observation of the holotype (IVPP V14533), we also noted alveoli in the premaxilla and maxilla; furthermore, the grooves and foramina observed in Archaeorhynchus (Zhou and Zhang, 2006) that indicate the presence of a beak are absent in Hongshanornis and Longicrusavis.”

“Notwithstanding the fact that this hypothesis and the monophyletic nature of “Sauriurae” have been rejected numerous times on cladistic terms (Chiappe 1995, 1996; Zhou and Zhang 2002; Clarke and Norell 2002; Clarke et al. 2006; O’Connor et al. 2009; Bell et al. 2010), the holotype of Rapaxavis pani clearly demon− stra…”

“Still other authors suggested that elongate tail feathers might have been associated with sexual display or visual communication (Chiappe et al., 1999, 2008; Zhang and Zhou, 2000; Clarke et al., 2006; Li et al., 2006, 2012; Zheng et al., 2007; O’Connor et al., 2011b, 2012, 2013; Padian and Horner, 2011).”

“Advanced ornithurans, which have musculoskeletal morphologies indicative of powerful flight comparable to extant birds [5,108,109] occur at least 50 million years before the oldest known neornithine [110,111].”

“According to the SBL results, the exceptions to this general decreasing trend are the nodes where chevron depth remained constant: proximal tail between node 14 and Ornithuromorpha (Ornithurae in middle tail), and between Neornithes and Neognathae.”

“The results are largely congruent with recent phylogenies of basal birds (Chiap- pe 2002; Clarke et al. 2006): Jeholornis and Archaeopteryx as consecutive outgroups of Pygostylia, Confuciusornis and Sapeornis as basalmost pygostylians, and a large ornithothoracine clade composed of Enantiornithes…”

“47), which are stem lineage representatives of Ornithurae and Neornithes respectively (Clarke et al., 2006), and may be plesiomorphic for neornithine birds.”

“The relative positions of basal ornithuromorphs proposed here are similar to those presented by Clarke et al. (2006) and Zhou & Zhang (2006b), but differ from those recovered by You et al. (2006), whose analysis placed Gansus within Ornithurae, closer to Neornithes than is Hesperornis.”

“The co-occurrence of rectricial fans only with the small plough-shaped pygostyle morphology suggests that these two features co-evolved with the rectricial bulbs as part of a ‘‘rectricial complex’’ [4].”

“…Yates and Kitching, 2003; Carrano, 2005; ornithischians, Mallison 2010a), ‘knee-driven’ bipedality (avialans, Gatesy and Middleton, 1997; Carrano, 1998; Rankin et al., 2016), and flight (theropods, Gatesy and Dial, 1996; Clarke et al., 2006; Heers and Dial, 2015; Chatterjee and Templin, 2007).”

“That same phalangeal formula is widely distributed in taxa that are crownward of Jinguofortisidae with a few exceptions (1, 7, 22, 24) until further reduction is seen in more crownward birds.”

“2009), suggest that the fan-shaped tail morphology evolved independently within each clade and support the hypothesis that the rectricial bulb may have co-evolved with the osteologically modern pygostyle within the ornithuromorph clade (Yixianornis [Clarke et al. 2006]; Hongshanornis [O’Connor et al.”

“Correlations between certain maniraptoran traits have been noted before, especially the co-incidence of short tails and the presence of a pygostyle [133].”

“Yixianornis providing the earliest evidence of a tail fan similar to that seen in extant birds [30], and Hongshanornis, with long primaries and alula, being able to fly fast in open areas with a slim and unslotted wing [31] are classified as ‘CF’ in PCA (figure 4a).”

“Insight into the evolution of avian flight from a new clade of Early Cretaceous ornithurines from China and the morphology of Yixianornis grabaui.”

“Among extinct avian theropods, a mesethmoid has been reported in enantiornithines (Clarke et al., 2006) and hesperornithiformes (Bühler et al., 1988; Clarke, 2004), although its presence in Archaeopteryx is ambiguous (Mayr et al., 2005).”

“By contrast, other analyses including ~200 characters from the whole skeleton and focused on Mesozoic stem-clade avian relationships (e.g., Clarke and Norell, 2002; Clarke, 2004; Clarke et al., 2006), consistently recover Lithornis nested within crown Aves as the sister taxon to the only extant palaeognath species exe…”

“The main difference is that Sapeornis occupies a more deeply nested position than the Confuciusornithidae within Pygostylia, and is the sister group to Ornithothoraces (Gao et al., 2008).”

“In this clade, other derived characteristics of crown group birds occurred that assist in refined flight control, such as a prominent extensor process of the carpometacarpus, which is an anatomical correlate of the automatic wing extension (Vazquez 1994), and a fanshaped tail (Clarke et al. 2006).”

“The highly-modified rectrices preserved in the new specimen and in other extinct maniraptoran dinosaurs may have similarly functioned in intraspecific communications, specifically ornamentation (Clarke et al. 2006; Li et al. 2012; Wang et al. 2014b; de Souza Carvalho et al. 2015).”

“In stark contrast to S. lii, the jugal in Y. grabaui and H. longicresta is unforked, and the bone is simply rod-like and bowed ventrally as in crown birds (Zhou and Zhang, 2005; Clarke et al., 2006).”

“…V13276; Zhou & Zhang 2002a), Shenzhouraptor sinensis (LPM 0193, Ji et al. 2002) Vescornis hebeiensis (NIGP 130722; Zhang et al. 2004), Yanornis martini (IVPP V 13358; Zhou & Zhang 2001), Yixianornis grabaui (IVPP V13631; Clarke et al. 2006) and Zhongornis haoae (DNHM D2455/6; Gao et al. 2008).”

“Furthermore, fan-shaped tails among Mesozoic birds have been previously clearly documented only within Ornithuromorpha, in association with a small, plow-shaped pygostyle of essentially modern appearance, and it is probable that the proximal fan and the pygostyle coevolved in this lineage (24).”

“The cladogram is largely consistent with previous studies regarding the placements of major clades (Clarke et al., 2006; Zhou et al., 2008, 2009; O'Connor et al., 2009; Wang et al., 2014b).”

“Interestingly, the forked jugal is also reported in a basal ornithuromorph Schizooura lii but absent in sympatric ornithuromorph Yixianornis grabaui (Clarke et al. 2006; Zhou et al. 2012).”

“A well-developed pisiform process forms a peg-like ventral projection (Figure 7(C)), similar to that of Apsaravis and Yixianornis (Clarke and Norell 2002; Clarke et al. 2006).”

“Preservation in previously described Early Cretaceous ornithuromorphs precluded an accurate estimate of the complete tail; Yixianornis IVPP V13631 preserves at least eight (59), and Hongshanornis DNHM2945/6 is reported to have a minimum of 10 (57).”

“Despite these objections, the close relationship between enantiornithines and ornithuromorphs is widely accepted, and alternative topologies have received little support in phylogenetic analyses (Clarke et al. 2006; O’Connor & Zhou 2013; Wang, Hu et al. 2015; Wang, Zheng et al. 2015).”

“[135], and new observations gathered by the authors for 38 terminal taxa.”

“The new cladogram is generally consistent with the result of previous analyses in the placement of most taxa (Clarke et al., 2006; Zhou and Zhang, 2006b; Zhou et al., 2008, 2010), with the main differences involving the positions of Sapeornis, Confuciusornithidae, and Apsaravis.”

“Within the enantiornithine sister clade, Ornithuromorpha, the largest subclade includes three taxa: Songlingornis linghensis, Yanornis martini and Yixianornis grabaui (Clarke et al. 2006).”

“Both the ulna and radius are more robust than those in Gansus (Table 1), while similar to those of Yixianornis, respectively (IVPP V13631; Figure 4) [20].”

“In contrast, Confuciusornithidae has been considered to be more derived than Sapeornis in some previous studies (Clarke et al. 2006; Zhou et al. 2008; O’Connor et al. 2013).”

“[74] recoversMaaqwi as sister to Vegavis (Fig 7) in approach to the terminal Cretaceous (Fig 8).”

“The Yixianornis + (Songlingornis + Yanornis) clade differs in struc− ture from previous analyses (Clarke et al. 2006) in that Ya− nornis and Songlingornis share a more exclusive relationship with each other than either does with Yixianornis; this pairing is supported by three synapomorphies (char.”

“There is no separation between the lesser and greater trochanters in Rahonavis; the two are confluent and form a single, symmetrical trochanteric crest (Figure 32.2, 32.6), like in many avialans (e.g., Yixianornis, Clarke et al., 2006; Confuciusornis, Chiappe et al., 1999; Archaeopteryx, BMMS 500).”

“Yixianornis, Jianchangornis and hongshanornithids, in which the alular digit reaches the distal margin of the major metacarpal (Clarke et al. 2006; Z. Zhou et al. 2009; M. Wang et al. 2015).”

“The predentary bone was not reported in previous descriptions of this bird (Zhou & Zhang 2001; Clarke et al. 2006).”

“…Zhou and Zhang, 2005, Piscivoravis lii Zhou et al., 2013, Yanornis martini Zhou and Zhang, 2001, Yixianornis grabaui; Zhou and Zhang, 2005; Clarke et al., 2006; Zhou et al., 2013) preserve large, round tails formed by a fan of 6–10 rectrices, and one taxon (Schizooura lii) has a forked…”