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Re: [dinosaur] Cranial ornamentation linked to rapid evolution of gigantic theropod dinosaurs (free pdf)



I came up with a similar idea a while ago: that the evolution of
pennaceous feathers allowed maniraptoans to use these as display
structures, rather than bony cranial crests.  As I put it (in 2008):

"Many non-avian theropods show bony structures that appear to have
been used for ornamentation, such as the assorted cranial crests,
horns, and bosses seen in certain coelophysoids, ceratosaurs, basal
tetanurans, carnosaurs, tyrannosaurs, and some basal coelurosaurs
(e.g., _Proceratosaurus_).  But these cranial structures are not as
prevalent in the maniraptorans (though some oviraptorosaurs had
casques), so it may be that the "medium" for sexual display was
shifted from the skull to the integument."

http: //dml.cmnh.org/2008Oct/msg00164.html
http: //dml.cmnh.org/2005Jun/msg00216.html


However, I didn't back up my idea with stats; and I didn't factor in
the role of body size.

Gates &c also make the point that "Birds, chameleons and iguanas
living in closed habitats have brighter plumage".  This might have
been especially true for small pennaraptorans from the Jehol biota
(including iridescence doi:10.1126/science.1213780).  This dovetails
with another idea, that small terrestrial pennaraptorans used their
wings for short leaps or fluttering hops in closed habitats.  The
smaller a terrestrial vertebrate, the greater its requirement to
negotiate broken or uneven terrain.

On Wed, Sep 28, 2016 at 1:07 AM, Ben Creisler <bcreisler@gmail.com> wrote:
>
> Ben Creisler
> bcreisler@gmail.com
>
> A new paper:
>
> Terry A. Gates, Chris Organ & Lindsay E. Zanno (2016)
> Bony cranial ornamentation linked to rapid evolution of gigantic theropod
> dinosaurs.
> Nature Communications 7, Article number: 12931 (2016)
> doi:10.1038/ncomms12931
> https://urldefense.proofpoint.com/v2/url?u=http-3A__www.nature.com_articles_ncomms12931&d=DQIBaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=4_oP2wn8cG1a9sT1N_ODX1V4h7Sbc1caXe4noIhmDF8&s=Z_tka1gZtcLiNk0H5ftsteJv40lFdxstJ6f6VFoxJyg&e=
>  
>
>
> Exaggerated cranial structures such as crests and horns, hereafter referred
> to collectively as ornaments, are pervasive across animal species. These
> structures perform vital roles in visual communication and physical
> interactions within and between species. Yet the origin and influence of
> ornamentation on speciation and ecology across macroevolutionary time scales
> remains poorly understood for virtually all animals. Here, we explore
> correlative evolution of osseous cranial ornaments with large body size in
> theropod dinosaurs using a phylogenetic comparative framework. We find that
> body size evolved directionally toward phyletic giantism an order of
> magnitude faster in theropod species possessing ornaments compared with
> unadorned lineages. In addition, we find a body mass threshold below which
> bony cranial ornaments do not originate. Maniraptoriform dinosaurs generally
> lack osseous cranial ornaments despite repeatedly crossing this body size
> threshold. Our study provides novel, quantitative support for a shift in
> selective pressures on socio-sexual display mechanisms in theropods
> coincident with the evolution of pennaceous feathers.
>
>