What reptiles gave rise to birds? Nicholas Gardner, Marshall University 19 August 2014 Nicholas Gardner, email@example.com, Marshall University Michael Hanson, firstname.lastname@example.org, Yale University Like EGL (2014), we were “unaware of the raging dispute over just what group of reptiles gave rise to birds”. Unfortunately for EGL, it is clear that he is equally unfamiliar with the body of literature that he joins Feduccia in dismissing. Though EGL writes “most of the fossils used to support the theropod ancestry of birds are 20 million or more years younger than Archaeopteryx”, he is unaware that the alleged temporal paradox for the theropod origins of birds has been well addressed. Multiple authors have tackled this fallacy head on (Brochu and Norell, 2000; 2001; Norell et al., 1998) and have been validated by the discovery of numerous pre-Archaeopteryx coelurosaurs (Choiniere et al., 2014; Godefroit et al., 2013a, b; Han et al., 2011; Hu et al., 2009; Maganuco et al., 2005; Xu et al., 2010; Zhang et al., 2008), but even then Jurassic maniraptorans have long been known (Evans and Milner, 1994; Metcalf and Walker, 1994; Zinke, 1998). Further, as pointed out before (Norell et al., 1998), all of the vaguely proposed alternatives to the theropod origins of birds – the poorly known Cosesaurus, drepanosaurids, or Longisquama are far worse. The latest known of these, uppermost Rhaetian drepanosaurids (Harris and Downs, 2002), still present a larger gap of 60 million years or more before Archaeopteryx. It is not clear how it is “more reasonable” for EGL to assert that flight in birds evolved by gliding. The earliest birds (Archaeopteryx included) appear to have been mostly ground-foragers, not arboreal (Dececchi and Larsson, 2011). The avian flight stroke appears to have been co-opted from other behaviors (Dial, 2003; Fowler et al., 2011) and its antecedent features are found in numerous theropod groups leading up to Avialae (Gatesy and Baier, 2005; Hutchinson and Allen, 2009; Senter, 2006; Sereno, 1999). There is also no reason to presume that arboreal and cursorial adaptations must be mutually exclusive (Dial, 2003; Dial et al., 2006). As a side note, EGL asserts pterosaurs must have had gliding ancestors, yet functional morphology and morphometric studies of Triassic pterosaurs supports that they too had terrestrial ancestors (Bell et al., 2011; Padian, 2008).EGL asserts that feathers must have evolved in connection with gliding and flying yet Longisquama, offered up many times as a possible avian ancestor by Feduccia (see Feduccia, 1993; Feduccia and Engstrom, 2003; Feduccia and Martin, 1998; Feduccia and Smith, 2002; Feduccia and Wild, 1993; Geist and Feduccia, 2000; Jones et al. 2000), shows long, unpaired scales on its back that could not have been used for parachuting or gliding as originally proposed (Buchwitz and Voigt, 2012; Prum, 2001; Reisz and Sues, 2000; Unwin and Benton, 2001; Voight et al., 2009; contra Haubold and Buffetaut, 1987). Even with placing maniraptoran dinosaurs as bird antecedents while attempting to claim they are not dinosaurs as Feduccia has been recently wont to do (Feduccia et al., 2005), the most primitive of these would still show feathers before the origin of birds or the origin of powered flight. Furthermore, the claim that feathers evolved in connection with gliding and flying infers a hypothetical structure based on a hypothetical ancestral function, such inferences of functions for structures cannot reliably be made in the absence of observations of living organisms, let alone fossil or hypothetical organisms (Prum, 1999). At the same time, most models for feather evolution centering on an aerodynamic function depend on the assumption that the modern contour feather structure is a plesiomorphic morphology, homologous with the flat, broad reptilian scale (Maderson, 1972; 2000). This view has been overturned in light of recent developmental and molecular evidence demonstrating the avian feather to be an evolutionary novelty with a unique tubular structure and keratin composition differentiating feathers from the reptilian scales, with the plesiomorphic condition likely being a tubular filament (Prum, 1999; 2005). EGL raises the idea that filamentous structures in Sinosauropteryx and Sinornithosaurus and other non-avian dinosaurs are in fact collagen fibers as proposed by Lingham-Soliar (2003; et al. 2007). Yet detailed study of these structures contradicts this. In fact, not only in gross morphology are these structures similar to feathers in being hollow and branching (Alibardi et al., 2009), but they also share the same melanosomes found in feathers (Li et al., 2010; Zhang et al., 2010). Feduccia and other authors (Feduccia, 1999; Martin, 2004; and references therein) long asserted before that many of these bird-like dinosaurs could not in fact be avian ancestors and were too different, but have begun including them as birds when they could not deny the numerous bird-like characters found in their integument and skeletons (Czerkas et al., 2002; Feduccia et al., 2005). This bears additional reflection in that Feduccia et al. (2005) simultaneously reject Sinornithosaurus as having feathers or feather-like structures (pp. 134-143), but then later decide that Sinornithosaurus and its deinonychosaurian relatives are secondarily flightless birds with feathers (p. 159 onward). Proponents of birds as anything but dinosaurs have never offered a clear alternative ancestor for birds. Neither drepanosaurids nor Longisquama have been recovered as archosauromorphs in wider analyses of reptile relationships. The drepanosaurids have been found either as lepidosauromorphs (Evans, 2009) or as stem-diapsids (Muller, 2004; Pritchard, 2014; Senter, 2004). Pairing birds with either would contradict indisputable molecular evidence favoring birds as archosaurs and any of the proposed bird-like characters (Feduccia and Wild, 1993) which drepanosaurids or Longisquama exhibit are also found in theropod dinosaurs along with countless others (Gauthier, 1986; Sereno, 1999) not present in either of these proposed avian predecessors. The Triassic reptile Cosesaurus from Spain, posited originally as a “proto bird” ( Ellenberger and de Villalta, 1974; Ellenberger, 1977; Martin, 1983), appears to be a basal archosauromorph and most of its bird-like characters were misinterpretations or again also found in theropod dinosaurs (Jalil, 1997; Milner, 1985; Olsen, 1979; Renesto, 1994; Sanz and Lopez Martinez, 1984). 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Palaontologische Zeitschrift 72 (1-2): 179-189. Competing interests The authors declare that they have no competing interests.