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Re: Alioramus (tyrannosaurid) and evolution of cranial pneumaticity in theropods



From: Ben Creisler
bcreisler@gmail.com

The pdf is now available for free on the AMNH site:

http://digitallibrary.amnh.org/dspace/handle/2246/6462

On Fri, Dec 6, 2013 at 12:18 PM, Ben Creisler <bcreisler@gmail.com> wrote:
> From: Ben Creisler
> bcreisler@gmail.com
>
> A new paper available on the BioOne site. It is not yet posted in open
> access on the AMNH site.
>
>
> Maria Eugenia Leone Gold, Stephen L. Brusatte and Mark A. Norell (2013)
> The Cranial Pneumatic Sinuses of the Tyrannosaurid Alioramus
> (Dinosauria: Theropoda) and the Evolution of Cranial Pneumaticity in
> Theropod Dinosaurs.
> American Museum Novitates Number 3790 : 1-46
> doi: http://dx.doi.org/10.1206/3790.1
> http://www.bioone.org/doi/abs/10.1206/3790.1
>
>
> [AMNH open access link:
> http://digitallibrary.amnh.org/dspace/handle/2246/9]
>
> Archosaurs and mammals exhibit skeletal pneumaticity, where bone is
> infilled by air-filled soft tissues. Some theropod dinosaurs possess
> extensively pneumatic skulls in which many of the individual bones are
> hollowed out by diverticula of three main cranial sinus systems: the
> paranasal, suborbital, and tympanic sinuses. Computed tomography (CT
> scanning) permits detailed study of the internal morphology of cranial
> sinuses. But only a few theropod specimens have yet been subjected to
> this type of analysis. We present CT scans of the remarkably preserved
> and disarticulated skull bones of the long-snouted tyrannosaurid
> theropod Alioramus. These scans indicate that Alioramus has extensive
> cranial pneumaticity, with pneumatic sinuses invading the maxilla,
> lacrimal, jugal, squamosal, quadrate, palatine, ectopterygoid, and
> surangular. Pneumaticity is not present, however, in the nasal,
> postorbital, quadratojugal, pterygoid, or angular. Comparisons between
> Alioramus and other theropods (most importantly the closely related
> Tyrannosaurus) show that the cranial sinuses of Alioramus are modified
> to fill the long-snouted skull of this taxon, and that Alioramus has
> an extreme degree of cranial pneumaticity compared to other theropods,
> which may be the result of the juvenile status of the specimen, a
> difference in feeding style between Alioramus and other theropods, or
> passive processes. Based on these comparisons, we provide a revised
> terminology of cranial pneumatic structures and review the
> distribution, variation, and evolution of cranial pneumaticity within
> theropod dinosaurs. This review illustrates that most theropods
> possess a common “groundplan” in which the maxilla and lacrimal are
> pneumatized, and that various theropods modify this groundplan by
> pneumatizing numerous other bones of the skull. Tyrannosaurids are
> very pneumatic compared to other theropods, particularly in the
> development of extensive ectopterygoid, quadrate, and palatine
> sinuses, as well as a pneumatic invasion into the surangular.
> Tyrannosauroids seem to retain many cranial sinuses, such as the jugal
> and nasal recesses, which are primitive for coelurosaurs but lost or
> apomorphically modified in taxa more closely related to birds.