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RE: Function and evolution of ankylosaur dermal armor




> Also, ankylosaurid plates with hollow
> bases are very thin in morphology and show thin compact
> bone. These results imply that the bone strengths of
> polacanthid spikes and ankylosaurid plates are lower than
> spikes and clubs of other ankylosaurs, indicating that
> they may be used more probably as display and/or
> thermoregulation rather than as weapons. It is thus
> probable that ankylosaur armor in general played more
> than just a defensive role.


Makes a wholelotta sense, considering that the dermal osteoderms of _Alligator 
mississippiensis_ - and, I'm assuming, other crocodilians as well - serve a 
thermoregulatory funtion. I'm pretty much convinced that stegosaur plates 
performed a similar purpose (and yes, I'm aware of the arguments con).

~ Michael


> Date: Sat, 23 Jan 2010 15:37:34 +0000
> From: bh480@scn.org
> To: dinosaur@usc.edu
> Subject: Function and evolution of ankylosaur dermal armor
>
> From: Ben Creisler bh480@scn.org
>
> In case this paper has not been mentioned yet:
>
> Shoji Hayashi, Kenneth Carpenter, Torsten M. Scheyer,
> Mahito Watabe, and Daisuke Suzuki.
> Function and evolution of ankylosaur dermal armor.
> Acta Palaeontologica Polonica in press
> available online 19 Jan 2010
> http://www.app.pan.pl/issue.html?issue=forthcoming
>
>
> Ankylosaurs have spike-, plate-, and club-shaped
> osteoderms probably used as defensive and/or offensive
> weapons. Previous studies have proposed the evolution and
> function of small ankylosaur osteoderms, but histological
> variations in their defensive weapons are little known.
> Here, we provide comparisons of the internal structures
> in defensive weapons of ankylosaurs, which shed light on
> understanding their evolutionary history and function.
> Histological features of spikes, plates, and clubs are
> similar to those of small osteoderms in having thin
> compact bone, thick cancellous bone with large vascular
> canals, and abundant collagen fibers. A previous study
> demonstrated that each of the three groups of ankylosaurs
> (the Polacanthidae, Nodosauridae, and Ankylosauridae)
> have distinct arrangements of collagen fibers in small
> osteoderms. This study shows that spikes and clubs of
> ankylosaurs maintain the same characteristic features for
> each group despite the differences in shapes and sizes.
> These histological similarities suggest that various
> types of osteoderms in ankylosaurs retained the thin
> compact bone and abundant fiber structures of the small
> osteoderms during their evolution. Polacanthid spikes
> show thin compact bone, with less collagen fibers than in
> spikes of nodosaurids and spikes and clubs of
> ankylosaurids. Also, ankylosaurid plates with hollow
> bases are very thin in morphology and show thin compact
> bone. These results imply that the bone strengths of
> polacanthid spikes and ankylosaurid plates are lower than
> spikes and clubs of other ankylosaurs, indicating that
> they may be used more probably as display and/or
> thermoregulation rather than as weapons. It is thus
> probable that ankylosaur armor in general played more
> than just a defensive role.
>
> Key words: Ankylosauria, Thyreophora, dermal armor, bone
> histology, evolution, growth, function.
>
>                                         
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