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[dinosaur] Scale-to-feather conversion + pterosaur palaeobiology + gnathostome vertebral skeleton + origin of digit patterning

Ben Creisler

Some new papers:

Ping Wu, Jie Yan, Yung-Chih Lai, Chen Siang Ng, Ang Li, Xueyuan Jiang, Ruth Elsey, Randall Widelitz, Ruchi Bajpai, Wen-Hsiung Li & Cheng-Ming Chuong (2017)
Multiple regulatory modules are required for scale-to-feather conversion.
Molecular Biology and Evolution, msx295, (advance online publication)
doi: https://doi.org/10.1093/molbev/msx295

The origin of feathers is an important question in Evo-Devo studies, with the eventual evolution of vaned feathers which are aerodynamic, allowing feathered dinosaurs and early birds to fly and venture into new ecological niches. Studying how feathers and scales are developmentally specified provides insight into how a new organ may evolve. We identified feather-associated genes using genomic analyses. The candidate genes were tested by expressing them in chicken and alligator scale forming regions. Ectopic _expression_ of these genes induced intermediate morphotypes between scales and feathers which revealed several major morphogenetic events along this path: localized growth zone formation, follicle invagination, epithelial branching, feather keratin differentiation and dermal papilla formation. In addition to molecules known to induce feathers on scales (retinoic acid, Î-catenin), we identified novel scale-feather converters (Sox2, Zic1, Grem1, Spry2, Sox18) which induce one or more regulatory modules guiding these morphogenetic events. Some morphotypes resemble filamentous appendages found in feathered dinosaur fossils, while others exhibit characteristics of modern avian feathers. We propose these morpho-regulatory modules were used to diversify archosaur scales and to initiate feather evolution. The regulatory combination and hierarchical integration may have led to the formation of extant feather forms. Our study highlights the importance of integrating discoveries between developmental biology and paleontology.






Free pdf:

David W. E. Hone, Mark P. Witton and David M. Martill (2017)

New perspectives on pterosaur palaeobiology.

Geological Society, London, Special Publication SP455: New Perspectives on Pterosaur Palaeobiology (advance online publication)




Pterosaurs were the first vertebrates to evolve powered flight and occupied the skies of the Mesozoic for 160 million years. They occurred on every continent, evolved their incredible proportions and anatomy into well over 100 species, and included the largest flying animals of all time among their ranks. Pterosaurs are undergoing a long-running scientific renaissance that has seen elevated interest from a new generation of palaeontologists, contributions from scientists working all over the world and major advances in our understanding of their palaeobiology. They have especially benefited from the application of new investigative techniques applied to historical specimens and the discovery of new material, including detailed insights into their fragile skeletons and their soft tissue anatomy. Many aspects of pterosaur science remain controversial, mainly due to the investigative challenges presented by their fragmentary, fragile fossils and notoriously patchy fossil record. With perseverance, these controversies are being resolved and our understanding of flying reptiles is increasing. This volume brings together a diverse set of papers on numerous aspects of the biology of these fascinating reptiles, including discussions of pterosaur ecology, flight, ontogeny, bony and soft tissue anatomy, distribution and evolution, as well as revisions of their taxonomy and relationships.


Free pdf:

Katharine E. Criswell, Michael I. Coates & J. Andrew Gillis (2017)
Embryonic origin of the gnathostome vertebral skeleton.
Proceedings of Royal Society B 284 1867 20172121;Â
DOI: 10.1098/rspb.2017.2121

The vertebral column is a key component of the jawed vertebrate (gnathostome) body plan, but the primitive embryonic origin of this skeleton remains unclear. In tetrapods, all vertebral components (neural arches, haemal arches and centra) derive from paraxial mesoderm (somites). However, in teleost fishes, vertebrae have a dual embryonic origin, with arches derived from somites, but centra formed, in part, by secretion of bone matrix from the notochord. Here, we test the embryonic origin of the vertebral skeleton in a cartilaginous fish (the skate, Leucoraja erinacea) which serves as an outgroup to tetrapods and teleosts. We demonstrate, by cell lineage tracing, that both arches and centra are somite-derived. We find no evidence of cellular or matrix contribution from the notochord to the skate vertebral skeleton. These findings indicate that the earliest gnathostome vertebral skeleton was exclusively of somitic origin, with a notochord contribution arising secondarily in teleosts.


Free pdf:

Thomas A. Stewart, Ramray Bhat and Stuart A. Newman (2017)

The evolutionary origin of digit patterning.


doi: https://doi.org/10.1186/s13227-017-0084-8






The evolution of tetrapod limbs from paired fins has long been of interest to both evolutionary and developmental biologists. Several recent investigative tracks have converged to restructure hypotheses in this area. First, there is now general agreement that the limb skeleton is patterned by one or more Turing-type reactionâdiffusion, or reactionâdiffusionâadhesion, mechanism that involves the dynamical breaking of spatial symmetry. Second, experimental studies in finned vertebrates, such as catshark and zebrafish, have disclosed unexpected correspondence between the development of digits and the development of both the endoskeleton and the dermal skeleton of fins. Finally, detailed mathematical models in conjunction with analyses of the evolution of putative Turing system components have permitted formulation of scenarios for the stepwise evolutionary origin of patterning networks in the tetrapod limb. The confluence of experimental and biological physics approaches in conjunction with deepening understanding of the developmental genetics of paired fins and limbs has moved the field closer to understanding the fin-to-limb transition. We indicate challenges posed by still unresolved issues of novelty, homology, and the relation between cell differentiation and pattern formation.



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