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Feather morphologies in early birds + Cretaceous ichthyosaurs (free pdfs)



From: Ben Creisler
bcreisler@gmail.com



These  papers in the Open Access journal Geosciences came out last
year but have not been mentioned yet on the DML. I missed them at the
time but better late than never...


Jingmai K. O’Connor, Luis M. Chiappe, Cheng-ming Chuong, David J.
Bottjer and Hailu You (2012)
Homology and Potential Cellular and Molecular Mechanisms for the
Development of Unique Feather Morphologies in Early Birds.
Geosciences 2(3): 157-177;
doi:10.3390/geosciences2030157
http://www.mdpi.com/2076-3263/2/3/157



At least two lineages of Mesozoic birds are known to have possessed a
distinct feather morphotype for which there is no neornithine (modern)
equivalent. The early stepwise evolution of apparently modern feathers
occurred within Maniraptora, basal to the avian transition, with
asymmetrical pennaceous feathers suited for flight present in the most
basal recognized avian, Archaeopteryx lithographica. The number of
extinct primitive feather morphotypes recognized among non-avian
dinosaurs continues to increase with new discoveries; some of these
resemble feathers present in basal birds. As a result, feathers
between phylogenetically widely separated taxa have been described as
homologous. Here we examine the extinct feather morphotypes recognized
within Aves and compare these structures with those found in non-avian
dinosaurs. We conclude that the “rachis dominated” tail feathers of
Confuciusornis sanctus and some enantiornithines are not equivalent to
the “proximally ribbon-like” pennaceous feathers of the juvenile
oviraptorosaur Similicaudipteryx yixianensis. Close morphological
analysis of these unusual rectrices in basal birds supports the
interpretation that they are modified pennaceous feathers. Because
this feather morphotype is not seen in living birds, we build on
current understanding of modern feather molecular morphogenesis to
suggest a hypothetical molecular developmental model for the formation
of the rachis dominated feathers of extinct basal birds.



==



Maria Zammit (2012)
Cretaceous Ichthyosaurs: Dwindling Diversity, or the Empire Strikes Back?
Geosciences 2(2), 11-24;
doi:10.3390/geosciences2020011
http://www.mdpi.com/2076-3263/2/2/11


Recent descriptions of new taxa and recognition of survivorship of
Jurassic genera across the Jurassic–Cretaceous boundary bring the
total number of Cretaceous ichthyosaur genera to eight. Taxa currently
known from the Cretaceous include Ophthalmosaurus, Caypullisaurus,
Aegirosaurus, Platypterygius, Maiaspondylus, Athabascasaurus,
Sveltonectes, and Acamptonectes. This review summarizes the occurrence
of all Cretaceous genera. A discussion of morphological diversity
demonstrates the different, though overlapping, ecological niches
occupied by the different taxa, while the comparison of phylogenetic
hypotheses shows the problems inherent in understanding the
evolutionary relationships between Cretaceous genera. The Late
Jurassic radiation indicated in the competing phylogenetic hypotheses
may correlate with the opening of the Atlantic Ocean or additional
dispersal routes established by the breakup of Gondwana. Inclusion of
the stratigraphically oldest Platypterygius species may aid in
resolving these evolutionary relationships.