Do feathered dinosaurs exist? Testing the hypothesis on neontological and paleontological evidence

Department of Biology, University of North Carolina, Chapel Hill, North Carolina 27599-3280, USA.
Journal of Morphology (Impact Factor: 1.74). 11/2005; 266(2):125-66. DOI: 10.1002/jmor.10382
Source: PubMed


The origin of birds and avian flight from within the archosaurian radiation has been among the most contentious issues in paleobiology. Although there is general agreement that birds are related to theropod dinosaurs at some level, debate centers on whether birds are derived directly from highly derived theropods, the current dogma, or from an earlier common ancestor lacking suites of derived anatomical characters. Recent discoveries from the Early Cretaceous of China have highlighted the debate, with claims of the discovery of all stages of feather evolution and ancestral birds (theropod dinosaurs), although the deposits are at least 25 million years younger than those containing the earliest known bird Archaeopteryx. In the first part of the study we examine the fossil evidence relating to alleged feather progenitors, commonly referred to as protofeathers, in these putative ancestors of birds. Our findings show no evidence for the existence of protofeathers and consequently no evidence in support of the follicular theory of the morphogenesis of the feather. Rather, based on histological studies of the integument of modern reptiles, which show complex patterns of the collagen fibers of the dermis, we conclude that "protofeathers" are probably the remains of collagenous fiber "meshworks" that reinforced the dinosaur integument. These "meshworks" of the skin frequently formed aberrant patterns resembling feathers as a consequence of decomposition. Our findings also draw support from new paleontological evidence. We describe integumental structures, very similar to "protofeathers," preserved within the rib area of a Psittacosaurus specimen from Nanjing, China, an ornithopod dinosaur unconnected with the ancestry of birds. These integumental structures show a strong resemblance to the collagenous fiber systems in the dermis of many animals. We also report the presence of scales in the forearm of the theropod ornithomimid (bird mimic) dinosaur, Pelecanimimus, from Spain. In the second part of the study we examine evidence relating to the most critical character thought to link birds to derived theropods, a tridactyl hand composed of digits 1-2-3. We maintain the evidence supports interpretation of bird wing digit identity as 2,3,4, which appears different from that in theropod dinosaurs. The phylogenetic significance of Chinese microraptors is also discussed, with respect to bird origins and flight origins. We suggest that a possible solution to the disparate data is that Aves plus bird-like maniraptoran theropods (e.g., microraptors and others) may be a separate clade, distinctive from the main lineage of Theropoda, a remnant of the early avian radiation, exhibiting all stages of flight and flightlessness.

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Available from: Alan Feduccia
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    • "It had a solution for the problem of digit homology, but at the same time the mosaic features of Archaeopteryx lithographica had to be explained as convergent evolution. Since the discovery of feathered dinosaurs more basal than Archaeopteryx (Ji et al., '98; Zhou et al., 2003; Xu et al., 2012), most researchers no longer consider a different origin of birds and dinosaurs, although others have argued that most of the " feathered dinosaurs, " the maniraptorans, actually represent an early radiation of birds, whereas filamentous traces in real dinosaurs may not be feathers (Feduccia et al., 2005). "
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    ABSTRACT: Avian forelimb digit homology remains one of the standard themes in comparative biology and EvoDevo research. In order to resolve the apparent contradictions between embryological and paleontological evidence a variety of hypotheses have been presented in recent years. The proposals range from excluding birds from the dinosaur clade, to assignments of homology by different criteria, or even assuming a hexadactyl tetrapod limb ground state. At present two approaches prevail: the frame shift hypothesis and the pyramid reduction hypothesis. While the former postulates a homeotic shift of digit identities, the latter argues for a gradual bilateral reduction of phalanges and digits. Here we present a new model that integrates elements from both hypotheses with the existing experimental and fossil evidence. We start from the main feature common to both earlier concepts, the initiating ontogenetic event: reduction and loss of the anterior-most digit. It is proposed that a concerted mechanism of molecular regulation and developmental mechanics is capable of shifting the boundaries of hoxD expression in embryonic forelimb buds as well as changing the digit phenotypes. Based on a distinction between positional (topological) and compositional (phenotypic) homology criteria, we argue that the identity of the avian digits is II, III, IV, despite a partially altered phenotype. Finally, we introduce an alternative digit reduction scheme that reconciles the current fossil evidence with the presented molecular-morphogenetic model. Our approach identifies specific experiments that allow to test whether gene expression can be shifted and digit phenotypes can be altered by induced digit loss or digit gain. J. Exp. Zool. (Mol. Dev. Evol.) 322B: 1-12, 2014. © 2013 Wiley Periodicals, Inc.
    Full-text · Article · Jan 2014 · Journal of Experimental Zoology Part B Molecular and Developmental Evolution
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    • "Since the first feathered non-avian theropod dinosaurs were discovered, the validity of the so-called protofeathers was called into question by some authors (especially for Sinosauropteryx Ji and Ji 1996) (after the International Code of Zoological Nomenclature to indicate who described the species), who interpreted the surrounding structures as degraded dermal collagen tissue (e.g. Feduccia et al. 2005; Lingham-Soliar et al. 2007). In this scenario, theropod dinosaurs with verifiable long pennaceous feathers (e.g. "
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    ABSTRACT: Dinosaurs with fossilized filamentous integument structures are usually preserved in a highly flattened state. Several different feather types have been described on this basis, but the two-dimensional preservation of specimens during fossilization makes the identification of single feather structures difficult due to overlapping feather structures in vivo. Morphological comparison with the diversity of recent feather types is therefore absolutely vital to avoid misinterpretation. To simulate the preservation process, a cadaver of recent Carduelis spinus (European siskin) was flattened in a printing press. Afterwards, the structure of the plumage was compared with the morphology of a single body feather from the same specimen. In comparison with the single feather, the body plumage of the flattened bird looked rather filamentous. It was almost impossible to identify single structures, and in their place, various artefacts were produced. The investigation of plumage in a specimen of the Mesozoic bird Confuciusornis sanctus reveals similar structures. This indicates that flattening of specimens during fossilization amplifies the effect of overlapping among feathers and also causes a loss of morphological detail which can lead to misinterpretations. The results are discussed in connection with some dubious feather morphologies in recently described theropods and basal birds. Based on recent feather morphology, the structure of so-called proximal ribbon-like pennaceous feathers (PRPFs) found in many basal birds is reinterpreted. Furthermore, the morphology of a very similar-looking feather type found in the forelimb and tail of an early juvenile oviraptorosaur is discussed and diagnosed as the first feather generation growing out of the feather sheath. Thus, the whole plumage of this theropod might represent neoptile plumage.
    Full-text · Article · Mar 2012 · Paläontologische Zeitschrift
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    • "These dynamic functions are largely determined by structural characteristics of the dermis, which in turn are dependent on a complex meshwork of collagen and elastin fibers [24]. The mechanical properties of skin and associated fibrous tissues have been examined in an array of extant vertebrate taxa, including bony fish [21], sharks [17]–[19], reptiles [17], cetaceans [25], [26], and birds [17]; however, given sparse preservation of soft-tissue structures (other than scales, hairs and feathers) our knowledge of the integumental fiber architecture in fossil vertebrates is hitherto limited to ichthyosaurs (e.g., [17], [27], [28]), pterosaurs (e.g., [29]) and dinosaurs (e.g., [22]). Hence, the discovery of an elaborate system of multiple-layered fiber bundles in FHSM VP-401 constitutes a significant development in so far as it represents the first unambiguous record of deeper soft-tissue structures in the skin of an extinct squamate (but see also [9]). "
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    ABSTRACT: The physical properties of water and the environment it presents to its inhabitants provide stringent constraints and selection pressures affecting aquatic adaptation and evolution. Mosasaurs (a group of secondarily aquatic reptiles that occupied a broad array of predatory niches in the Cretaceous marine ecosystems about 98-65 million years ago) have traditionally been considered as anguilliform locomotors capable only of generating short bursts of speed during brief ambush pursuits. Here we report on an exceptionally preserved, long-snouted mosasaur (Ectenosaurus clidastoides) from the Santonian (Upper Cretaceous) part of the Smoky Hill Chalk Member of the Niobrara Formation in western Kansas, USA, that contains phosphatized remains of the integument displaying both depth and structure. The small, ovoid neck and/or anterior trunk scales exhibit a longitudinal central keel, and are obliquely arrayed into an alternating pattern where neighboring scales overlap one another. Supportive sculpturing in the form of two parallel, longitudinal ridges on the inner scale surface and a complex system of multiple, superimposed layers of straight, cross-woven helical fiber bundles in the underlying dermis, may have served to minimize surface deformation and frictional drag during locomotion. Additional parallel fiber bundles oriented at acute angles to the long axis of the animal presumably provided stiffness in the lateral plane. These features suggest that the anterior torso of Ectenosaurus was held somewhat rigid during swimming, thereby limiting propulsive movements to the posterior body and tail.
    Full-text · Article · Nov 2011 · PLoS ONE
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