Exceptional dinosaur fossils show ontogenetic development of early feathers

Abstract

Recent discoveries of feathered dinosaur specimens have greatly improved our understanding of the origin and early evolution of feathers, but little information is available on the ontogenetic development of early feathers. Here we describe an early-juvenile specimen and a late-juvenile specimen, both referable to the oviraptorosaur Similicaudipteryx, recovered from the Lower Cretaceous Yixian Formation of western Liaoning, China. The two specimens have strikingly different remiges and rectrices, suggesting that a radical morphological change occurred during feather development, as is the case for modern feathers. However, both the remiges and the rectrices are proximally ribbon-like in the younger specimen but fully pennaceous in the older specimen, a pattern not known in any modern bird. In combination with the wide distribution of proximally ribbon-like pennaceous feathers and elongate broad filamentous feathers among extinct theropods, this find suggests that early feathers were developmentally more diverse than modern ones and that some developmental features, and the resultant morphotypes, have been lost in feather evolution.

Likelihood reinstates Archaeopteryx as a primitive bird

“…Powered, forewing-only flight typical of modern birds has been generally inferred to be present only in Archaeopteryx and other birds [2,5,20]. The flight capabilities of some deinonychosaurs remain contentious: the most proficient, Microraptor gui, used both the forelimbs and hindlimbs, and has been argued to be a glider [21] and asymmetric pennaceous feathers indicating aerodynamic ability are known only in dromaeosaurus outside of birds [22]. The likelihood-based phylogenies are consistent with a single origin of typical forewing-driven flight with no losses in basal birds (i.e.…”

“…Resolution of the precise position of Archaeopteryx will likely require more empirical data such as new fossils or novel characters. The alternative placements of Archaeopteryx highlight the closure of the morphological gap between birds and theropod dinosaurs [2][3][4][5][6]17,22], and also suggest that dramatic reinterpretations of early bird evolution are not yet required. Furthermore, the more generally accepted tree, found with likelihood-based methods (and the strong contrast with parsimony), suggests that likelihood-based phylogenetic methods should be used more often in palaeontology and morphology [24], especially for large datasets [3] that have sufficiently large numbers of characters to allow critical parameters in likelihood models to be robustly estimated.…”

When hatchlings outperform adults: locomotor development in Australian brush turkeys (Alectura lathami, Galliformes)

“…Caudipteryx [36,37]; Velociraptor [38]) that perhaps generated useful aerodynamic forces only for the diminutive juveniles. Recently, Xu et al [39] reported a dinosaur, Similicaudipteryx, that appears to exhibit changing feather morphology with age. This implies that different age classes may have enjoyed different locomotor capacities.…”

Nanomechanical properties of bird feather rachises: exploring naturally occurring fibre reinforced laminar composites

“…Although these structures are now known from fossils comprising almost all major paravian theropod dinosaur lineages [4][5][6][7][8], the b-keratin protein that makes up the feathers of living birds has long been thought to be a unique synapomorphy of the avian lineage (Aves/Avialae depending on usage) [9]. From the fossil record, we know that flight feathers on the forewings of dinosaurs have been evolving since at least the latest Jurassic [10] under two basic evolutionary pressures; to be light enough to facilitate flight and to be strong enough to sustain aerodynamic loading [11,12].…”