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Re: Kentrosaurus sexual dimorphism and Tarbosaurus juvenile skull



Is the May JVP out yet? We don't have it online yet so I 
assume it isn't out in hardcopy yet either. 


--- On Mon, 5/9/11, bh480@scn.org <bh480@scn.org> wrote:

> From: bh480@scn.org <bh480@scn.org>
> Subject: Kentrosaurus sexual dimorphism and Tarbosaurus juvenile skull
> To: dinosaur@usc.edu
> Date: Monday, May 9, 2011, 8:51 PM
>
> From: Ben Creisler
> bh480@scn.org
> 
> 
> In addition to the new dinosaurs Arcusaurus and Haya, the
> May JVP has two
> other dinosaur-related papers:
> 
> I had an earlier posting on this one based on news stories
> and press
> releases:
> 
> Takanobu Tsuihiji; Mahito Watabe; Khishigjav Tsogtbaatar;
> Takehisa
> Tsubamoto; Rinchen Barsbold; Shigeru Suzuki; Andrew H. Lee;
> Ryan C.
> Ridgely; Yasuhiro Kawahara; Lawrence M. Witmer 
> (2011)
> Cranial osteology of a juvenile specimen of Tarbosaurus
> bataar (Theropoda,
> Tyrannosauridae) from the Nemegt Formation (Upper
> Cretaceous) of Bugin
> Tsav, Mongolia.
> Journal of Vertebrate Paleontology 31(3): 497 - 517 
> DOI: 10.1080/02724634.2011.557116 
> http://www.informaworld.com/smpp/content~db=all~content=a937433397~frm=absli
> nk
> 
> A juvenile skull of the tyrannosaurid Tarbosaurus bataar
> found in the Bugin
> Tsav locality in the Mongolian Gobi Desert is described.
> With a total
> length of 290 mm, the present specimen represents one of
> the smallest
> skulls known for this species. Not surprisingly, it shows
> various
> characteristics common to juvenile tyrannosaurids, such as
> the rostral
> margin of the maxillary fenestra not reaching that of the
> external
> antorbital fenestra and the postorbital lacking the cornual
> process. The
> nasal bears a small lacrimal process, which disappears in
> adults. Lacking
> some of the morphological characteristics that are adapted
> for bearing
> great feeding forces in adult individuals, this juvenile
> specimen suggests
> that T. bataar would have changed its dietary niches during
> ontogeny. The
> numbers of alveoli in the maxilla (13) and dentary (14 and
> 15) are the same
> a
etically in
> T. bataar and thus are not consistent with the hypothesis
> that the numbers
> of alveoli decreases ontogenetically in tyrannosaurids. 
> 
> 
> Holly E. Barden & Susannah C. R. Maidment (2011)
> Evidence for sexual dimorphism in the stegosaurian dinosaur
> Kentrosaurus
> aethiopicus from the Upper Jurassic of Tanzania. 
> Journal of Vertebrate Paleontology 31(3): 641--651
> DOI: 10.1080/02724634.2011.557112 
> http://www.informaworld.com/smpp/content~db=all~content=a937432642~frm=title
> link
> 
> Sexual dimorphism, the condition whereby males and females
> differ from one
> another physically, is one of the most fundamental aspects
> of the biology
> of any animal. However, sexually dimorphic characters can
> be subtle and are
> mainly related to soft tissue anatomy. They are, therefore,
> difficult to
> identify reliably in the fossil record particularly when
> dealing with small
> sample sizes and osteology alone. The first geometric
> morphometric analysis
> of dimorphism in a thyreophoran (armored) dinosaur shows
> that the femora of
> the stegosaurian dinosaur Kentrosaurus aethiopicus (Upper
> Jurassic,
> Tanzania) bear a statistically significant shape difference
> of the proximal
> end, which is independent of size and is therefore proposed
> to be a sexual
> difference. Although the disarticulated nature of the
> material means that
> intraspecific variation in other skeletal elements, such as
> the enigmatic
> dermal armor, cannot be identified as sexual dimorphism at
> this time, this
> study provides a methodology for further work on
> articulated stegosaurian
> specimens and has the potential to reveal additional
> information regarding
> the palaeobiology and population dynamics of this poorly
> understood clade. 
> 
> 
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