BCF
Does Caudipteryx represent an evolutionary step towards flight from flightless dinosaurs, or is it secondarily flightless from an already volant ancestor?
Many establishment Paleontologists continue to hold the view that the feathered early Cretaceous basal maniraptoran Cadipteryx, classified as a theropod dinosaur, represents a transition from non-flying dinosaurs to volant birds, As such, they will not accept the view that Caudipteryx is secondarily flightless. They hold this view because it is more parsimoniously indicated by their cladograms. They instead offer that some early dinosaur became more diminutive in size; developed feathers for display; later evolved wings for catching bugs, high jumping, or flapping while running up a log; and only then learned to fly. No amount of logical proof can convince them that Caudipteryx had flying ancestors.
Scanscoriopteryx and the Styliform Element
Feathered head of Xi Qi,
A new Scanscoriopteryx fossil was found in China, covered with feathers, possessing a “styliform element”, and said to sport a membrane attached to its arms resembling a bat’s wings. Scanscoriopteryx is a middle Jurassic maniraptor, considered by some to be a basal oviraptor.
A bizarre Jurassic maniraptoran theropod with preserved evidence of membranous wings-- Xing Xu et all
…Because other amniotes that possess a styliform element invariably utilize this structure to support an aerodynamic membrane that contributes to gliding or powered flight, and alternative functions for a long, unjointed rod of bone or cartilage extending from a distal limb joint are difficult to imagine , the occurrence of a styliform element in Yi is a strong indication that membranous aerodynamic surfaces and some degree of aerial capability were present in this taxon.
Most surprisingly, Yi has a long rod-likebone extending from each wrist, and patches of membranous tissue preserved between the rod-like bones and the manual digits. Analogous features are unknown in any dinosaur but occur in various flying and gliding tetrapods
In predicting the exact layout of the bones and wing in life, the authors compare it to a number of extant and extinct flying taxon and mammals, barely mentioning: “similar structures are present in the wrists of all pterosaurs.”
Possible wing configurations and position of styroform element of Xi Qi as suggested by authors:
lse = left styliform element;
rse = right styliform element;
Caudipteryx and the Propatagium
Ornithologist Allen Feduccia (2015) has discovered propatagiums on the Caudipterex fossils.
Protopatagium as found on the wings of Archaeopteryx and the modern duck.
Feduccia states: “The importance of a propatagium to the evolution of the avian wing is significant, as it has no apparent function other than contributing to the aerodynamics of the animal... The discovery of a propatagium in members of all clades of core maniraptorans... is additional evidence that flight was basal in Aves….The loss of flight is of such common occurrence within Aves that it should be expected to have occurred any time after flight was initially achieved.”
He concludes: "The revelation that Maniraptora consists of volant and neoflightless types of birds resolves many of the problematic issues… Recognizing that flightless members of Maniraptora are neoflightless may answer the question of where the secondarily flightless birds of the Mesozoic have been hiding".
Source: Testing the Neoflightless Hypothesis: Propatagium Reveals Flying
Ancestry of Oviraptorosaurs; Alan Feduccia, Stephen A. Czerkas; J Ornithol (2015) 156:1067–1074
Czerkas and Ji, 2002 pycnofibers were an antecedent of proto-feathers actinofibrils (internal structural fibers) in the wing membrane.
Date results indicate that the feathered dinosaurs of China were present more than 161 Ma ago, unquestionably older than Archaeopteryx in Germany, and are the earliest known feathered dinosaurs in the world. Furthermore, feathers appeared in ornithischians before 159 Ma rather than late in the Early Cretaceous. The known transitional pterosaurs first emerged before 161 Ma.
My comment: The fact that Archaeopteryx, usually deemed the first bird by definition, is much older than the bird-like theropods, does not dissuade most Paleontologists from claiming that said theropods represent the transitional dinosaurs that evolved into the birds. This dating further establishes that many new feathered and winged dinosaurs were not only older than the Cretaceous bird-like theropods, but even older than Archaeopteyx.
Timing of the earliest known feathered dinosaurs and transitional pterosaurs older than the Jehol Biota. Yong-Qing Liu a,⁎, Hong-Wei Kuang a, Xiao-Jun Jiang a, Nan Peng b, Huan Xu a, Hui-Yi Sun; Palaeogeography, Palaeoclimatology, Palaeoecology 323–325 (2012) 1–12