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Re: Kentrosaurus sexual dimorphism and Tarbosaurus juvenile skull

"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."


Lee Hall
Museum of the Rockies-Montana State University

On Mon, May 9, 2011 at 7:51 PM, bh480@scn.org <bh480@scn.org> wrote:
> 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
> as those in adults, suggesting that they do not change ontogenetically 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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