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Archived Comments for: Alan Feduccia’s Riddle of the Feathered Dragons: what reptiles gave rise to birds?

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  1. What reptiles gave rise to birds?

    Nicholas Gardner, Marshall University

    19 August 2014

    Nicholas Gardner,, Marshall University

    Michael Hanson,, 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).

    The long chains of shared characters—not just bones but also behavior, development, physiology, and soft tissues—all point towards an origin of birds deep from within theropod dinosaurs. Feduccia et al. have yet to provide a better supported alternative for the origin of birds.

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    Competing interests

    The authors declare that they have no competing interests.

  2. Comments on Nick Gardner (and Michael Hanson) on E G Leigh Jr.'s review of Feduccia’s Riddle of the Feathered Dragons

    John Jackson, independent

    13 November 2014

    NG violates not merely scientific but moral principles, by pretending he knows of no dispute. Not only are his group's views the only ones that count, they are the only ones that exist. His vehemence clearly proves the existence and depth of the dispute of course, but failure to represent the theoretical landscape is not just bad scientific practice (all research projects require honest reporting of others' views), it's the most common form of scientific fraud in historical science today. The sociological dimension of this subject now challenges the central themes for interest; as far as I'm concerned the main questions on the evolution of dinobirds have indeed been solved, though relevant disciplines long-neglected by NG and his co-theorists needed to be resourced (Jackson 2012). Not one author in the literature NG cites has qualifications or experience essential for interpreting cladograms. Felsenstein is absent. I'm absent. Pete Wagner is absent. Also absent are Osmolska, Olshevsky, James and Pourtless (2009) and Greg Paul, though Czerkas' inclusion proves NG knows of a dispute. But to move on from the central problem to consider the symptoms... Near the beginning of his critique, NG mentions the temporal paradox of a dinobird such as Deinonychus supposedly being ancestral to the 80mys-earlier-Archaeopteryx. However, more annoying, and much more characteristic of this scientific mess, was its paradoxical psychological aspect: why was the alternative Archaeopteryx to Deinonychus path permanently rejected from serious consideration right from the start? It¿s slightly different now but the fossils still present NG with a problem: Archaeopteryx' relatives have been found near and just before Archaeopteryx in time, revealing an explosion of long-armed fossils just when those long arms were presumably being used by it and its near ancestors, for aeronautics. And the evolution of flight would lead to an explosion. This time, the annoying paradox is: why was this possibility also permanently rejected from serious consideration right from the start? It avoids the extra unparsimonious complication of some other "Activity X" that these types were supposedly using their long arms for, which miraculously needed exactly the same adaptations that primitive flight needed, yet which remains unexplained. But the sword of science for cutting through all these theorisation issues should be: find the theory that best explains the observations. This is The Scientific Principle, and the theory that small forest-dwelling gliders gave rise to Archaeopteryx and its slightly earlier and more primitive relatives we're now finding, fits the observations very well. Their small bones dissolve in the acid soils of the forests they needed; we wouldn't expect them to fossilise often; and anyway the Jurassic is notorious for gaps. So fragile are these types, that from about 160mya, most of them are only found when conditions were so perfect that even their feathers fossilised. "It is not clear how it is 'more reasonable' for EGL to assert that flight in birds evolved by gliding." The clarity arises because it is absolutely imposssible to formulate the alternative: of any remotely evolutionarily feasible pathway direct to powered flight, through running along the ground and flapping unspecialised forelimbs. Anyone who has spent years investigating evolutionary processes through simulated natural selection, as I, but none of Gardner or his co-theorists, have done, will understand this. They need only present a single possible pathway that doesn't require a myriad tricky but instantaneous adaptations, but they cannot offer one. "The avian flight stroke appears to have been co-opted from other behaviors (Dial, 2003; Fowler et al., 2011)..." The floating of an impossible theory does not constitute "appears to have been". Abandoning front claw usage, but suddenly sprouting aerodynamic well-feathered wings with the full muscle, bone and nerve back-up for the specialised and very different activity, requires the magic trick: "With one bound, it evolved the seventeen different requirements for thrust-generating wings!" EGL asserted that flight in birds evolved by gliding, because that theory explains the observations well. Dial, Fowler and others, with their "Inclined Plane" and other such notions, have invented a theory refuted by the very evidence it's designed to explain. Nothing remotely resembling any stage of such a process is seen in extant species with no flying inheritance, yet intermediate stages of "tree-down" most certainly are. "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 (refs), shows long, unpaired scales on its back that could not have been used for parachuting or gliding as originally proposed (refs)." Odd, then, that they were ideally configured for gliding; odd also that NG is so certain that they were not paired, when those on the other side could so easily have not been preserved, or indeed might remain hidden within the fossil. The invisible set of legs down the other side of Hallucigenia, from the Burgess shale, had us all puzzled until we realised that "not apparent" did not mean non-existent. Many of NGs friends claimed for years that a left leg from the best known Protoceratops fossil did not exist, until I showed how you needed to look from the right hand side. And it's not just Longisquama. Weird features (paired bones hinged to the backbone) of the drepanosaur Megalancosaurus, hinted at by NG, and weird features on Protoavis (bumps on the forelimbs), conveniently forgotten by him, can both be accounted for by the same powerful explanation: they both supported feathers. A vast host of observations are accounted for by feathers in all sorts of early types, and feathers most clearly do appear to have preceded both "birds" and "dinosaurs". But Longisquama is at best an example of a late-surviving descendant of an earlier ancestor of birds, and may have diverged somewhat from that ancestor; a preferable example is Protoavis, which I cover thoroughly in Jackson (2012). "Furthermore, the claim that feathers evolved in connection with gliding and flying infers a hypothetical structure,..." We have more direct evidence for Triassic feathers than we have, for example, for blood, or neurons at that time. Feathers must have had various early forms; it is absolutely necessary to hypothesise that forms earlier than those of the type borne by Archaeopteryx existed. Indeed, it would be unacceptable not to. "...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)." The idea that animals glided 200mya is no risky hypothetical leap - and besides such activity is of course observed in living organisms! And neither he nor Prum have noticed that "inclined plane" type activities lack modern relevant exemplars among non-flying species. NG continues with the claim that genetic evidence suggests feathers are an evolutionary novelty, and have nothing to do with reptilian scales. Though they share many genetic mechanisms, feathers do of course differ greatly from lizard scales which for example slough together as a sheet, though they have a lot more in common with turtle, and even more with crocodilian, scales. In fact though, genetic research suggests that the parallel rows of structures appearing on either side of the spines of embryonic birds and crocodilians (and in all likelihood numerous archosaurs such as Agustinia, Desmatosuchus, stegosaurs etc.), though not mammals or lizards, share a deep common ancestry. But of course, the detailed mechanism through which a stegosaur dorsal plate was produced will differ enormously from a bird's feather tracts, just as both differ from a croc's parallel scutes. Being very different today does not mean that bird feathers and croc scales did not arise from a common feature shared by archosaurs and probably their ancestors post the split from the lizard lineage, and used for a purpose developed by birds but abandoned by crocs. "Proponents of birds as anything but dinosaurs have never offered a clear alternative ancestor for birds." In fact a very clear scheme has been proposed (Jackson 2012), where an arboreal gliding lineage, for which we are lucky enough to have examples from many stages, progressively spawned larger grounded forms, in agreement with the scheme EGL noted. This honours the relentless requirement for choosing theories that explain the observations the best, though it renders redundant certain concepts used in alternative theories, as it is entitled to do. "Theropod" is dissolved, as numerous lines evolve into large ground "theropod" forms, resulting each time in shortening arms, not as a single process, but repeatedly, and at different times. NG does not notice that this "alternative" has been offered; he started by saying "...we were 'unaware of the raging dispute over just what group of reptiles gave rise to birds'." He pretends to be unaware because he pretends that, for example, my 2012 book explaining all this (albeit often through essential disciplines which he and his colleagues may not have mastered), does not exist. A good scientist would have enough honesty not to do that, but also would have enough courage to pay attention to new ideas not just slightly different from their own, but radically different. Thus, when he says: "Neither drepanosaurids nor Longisquama have been recovered as archosauromorphs...", he shows he is not only still assuming that his cladograms cannot be questioned (it is well established that they must be), but he is assuming no theory could be right that suggests feathers started far, far earlier in the tree than he supposes. In addition to the stubbornness, and then the failure to realise that techniques under question don't qualify in the argument as a reliable source of truth, NG then makes an obvious elementary error by trying to draw support for his phylogeny from the "shared characters¿not just bones but also behavior, development, physiology, and soft tissues" ...between Cretaceous "theropods" and early birds. He is claiming simple similarity between types, as evidence for a direction of descent! Such is the nature of his group of co-theorists that this error has been repeated in the majority of their expositions of any length, for decades. I suggest that this is not, as one might suppose, inescapable evidence for feeble-mindedness (though the very bright would stop committing after it the first couple of times it had been pointed out), but that it can be explained, at least the first time, as a simple slip that arises from never having made a genuine effort to see their opponents' point of view. But then that is characteristic of the type of mediocre scientist who has leapt to block scientific advances for thousands of years. Scientific thinking is sometimes not just subtle, but weird: even though your argument seems right in many ways, it can still be wrong overall. Poor scientific thinking, backed up by stubbornness, groupism, and inadequate understanding of the many component subjects underlying the field as a whole, produces the situation complained about by Feduccia, noticed by Leigh, and exemplified by NG. NG did mention two further issues in Feduccia's writing that need addressing. The first is Feduccia's continued adherence to the view that certain apparently featherish filaments in some fossils are actually collagen fibers. I'm afraid we just have to try to ignore that, as we would try to ignore the persistent wearing of a silly hat by a good friend. It certainly doesn't destroy all his arguments, though it does suggest he doesn't see all archosaurs as ancestrally feathered: the fibres not just of Sinornithosaurus but also of Sinosauropteryx are both from aeronautic feathers, fibrous in their case, though it was only Sinosauropteryx' distant ancestors that merely glided on them many millions of years earlier, which it retained for other purposes (obligate bipeds have needed to be warm-blooded since the perpetual warmth near the P-T boundary), whereas Sinornithosaurus was still using them for powered flight. The second is Feduccia's change of mind that dromaeosaurs such as Sinornithosaurus might be closely related to birds and/or Archaeopteryx after all. NG mentions an apparent contradiction over this in Feduccia et al. (2005), and in Jackson (2012) I mentioned a similar example in Feduccia et al. (2007). Well, good scientists do change their minds, and many in this argument don't. It does seem odd that Feduccia seems to have been stuck in an intermediate stage for so long, but if NG's gang genuinely seeks a fully cogent solution to this field, it's illogical and fraudulent to ignore the one I've provided. References: Jackson, J. V. (2012) The Secret Dinobird Story. Amazon. Feduccia, A., Martin, L.D. and Tarsitano, S. (2007) Archaeopteryx 2007: Quo Vadis? The Auk, 124(2), 373¿380. James, F. C., Pourtless J. A. (2009) Cladistics and the Origin of Birds: A Review and Two New Analyses Ornithological Monographs 66, 1¿78. Other references are to be found at the end of NG and MHs comment, and in the references listed in Jackson (2012).

    Competing interests