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

Abstract

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.

Exceptionally preserved juvenile megalosauroid theropod dinosaur with filamentous integument from the Late Jurassic of Germany

“…These structures most likely represent collagen fibers within the stratum compactum of the dermis, which is characterized by a high density of collagen bundles in birds (43). The fibers clearly are different from the filaments in their orientation and their luminescence under filtered UV light and thus provide evidence against the interpretation of similarly arranged and oriented filaments in Chinese theropods as decaying collagen fibers (46,47).…”

Birth and death of cells in limb development: A mapping study

“…The ANZ and PNZ of the chick limb bud have been correlated with the evolutionary reduction in the number of digits typical of the normal pentadactyl limbs. Birds lose digit 1 and 5 in the wing (Feduccia et al, 2005) and severely reduce digit 5 in the leg. However, an alternative view proposes that the remaining digits in the bird wing represent digits 1, 2, and 3 by virtue of an anterior shift in the genetic developmental pathway that directs digit identity (Wagner and Gauthier, 1999;Vargas and Fallon, 2005).…”

“…However, sculpturing of the hand plate by removal of the interdigital tissue (as occurs in reptiles, birds, and mammals) is not the only way of making free digits, as exemplified by the amphibian forelimb, where the digits form by differential growth without participation of cell death (e.g., as demonstrated in Xenopus by Cameron and Fallon, 1977). In some cases such as the bird wing, cell death also plays a role in limb reconstruction and remodeling (e.g., removal of the ulnare cartilage from the wrist; Hinchliffe and Hecht, 1984) and specialization of the digits (e.g., digit 4; Feduccia et al, 2005). In amniotes, differential growth also participates in the separation of the digits (Salas-Vidal et al, 2001).…”

Rhetoric vs. reality: A commentary on “Bird Origins Anew” by A. Feduccia

“…Although we find it difficult to believe that, as the article states, ''a growing number of ornithologists are questioning the dinosaurian origin of birds'' (Feduccia 2013:1), if true, there can be no better motivation to address the points that were deftly woven into a seemingly cogent argument. In much the same way as creationists rebooted their flawed arguments against evolution by rebranding them as ''intelligent design,'' the recent Perspectives in Ornithology article (Feduccia 2013) attempts to resurrect arguments (see Feduccia 2002, Feduccia et al 2005 against the dinosaurian origin of birds that have been scientifically refuted (e.g., Prum , 2003. Spurious conclusions are yielded by an increasingly blurry focus on an ever smaller subset of available data as well as misunderstanding of the application of contemporary, field-normative phylogenetic methods and the theoretical support for those methods.…”